Professor Fred Crowe. Oregon State University – Talk Transcription
I have Chris and others found a patch of white rot that we’ll go visit
after lunch and we did bring in a couple of plants, and I guess what I
suggest after thinking about it, is after I run through some of the other
garlic diseases, and once I start on white rot, maybe people can come up
while I’m talking and individually look. I didn’t want to put a lot of
material around the room because there’s some risk that with dirty material
like this that it could get out and we don’t want it to get out. So keep it
in the tray here and I’ll just tell you ahead of time that there
s three pieces here and the two bulbs, just look at the general aspect of them,
the white fluffy mold and dirt, the one that’s just a piece of stem is where
you’re going to see the sclerotia best, and you don’t have to turn it, just
In my younger days I talked to some garlic growers and I thought I’d play
a practical joke. I very quickly found out that with a real serious disease
like this that farmers don’t have much of a sense of humour. What I did is
I got a bunch of poppy seeds in a vial and accidently spilled it across the
audience. Well they weren’t very happy and I very quickly explained that it
wasn’t really white rot before I got attacked, so I won’t do that any more.
So we don’t want to drop this on the floor, or if you want to take it home
with you that’s fine, but don’t leave it here. As far as I know there’s no
white rot at this horticultural centre and we want to leave it in the tray.
I have a couple of reference books up here that you may already have or may
want to know about. One of them is Canadian, I think it’s excellent, it’s
Diseases and Pests of Vegetable Crops in Canada, I think it’s produced out
of Ontario, I’m not 100% sure. I have it opened to some pictures of white
rot, but it’s really good across the board, the chapter and then there are
plates and I just have it opened to the plates.
Another one is one that is done by a lady out of the U.K. and it’s really
addressing post harvest problems, it’s a two volume issue and I brought the
one with onions and garlic in it. She does an excellent job on that.
And I think it’s a super reference to have in terms of post harvest generally.
The other one is American Phytopath Society Compendium, you may be familiar
with this series, they have at least dozens and if not hundreds of
different compendia on various crop and cropping groups. And this one on
onions and garlic was probably done about ten years ago and it’s in the process
of being reprinted this year and updated so you can order it but if you order
it make sure that you order the new issue which should be out almost any day,
but if they send you the old one make sure you get the new one because it’s
improved in a number of ways, and they try to regularly reissue this as
frequently as they need to on any given product to keep it up to date
because it’s supposed to be the latest possible information.
I’m rushing home after this to get ready for regular field day, plot tour,
on my research centre in central Oregon. Where a lot of industry people
out of California, Nevada and Washington will come and look at, basically,
fungicide trials, so I walk both sides of the line here on conventional
and organic. For many years I’ve worked with the large California industry
because we grow a lot of the seed garlic in central Oregon.
In background I did my Ph.D. in I was down in (?) production.
I’ve also in the last couple of years become a small boutique variety of
organic garlic grower and this fall we’re going to become organic so I’m
joining a lot of you in that sense I guess.
I’ll eventually get to the point of diagnosis and what I think is a realistic
program, at least for some of you, of maintenance if you already have white
rot, but white rot is a lot easier to control if you never get it and prevent
it. You kind of have to learn the fine line between paranoia neuroses and
reality in avoiding it, so we’ll talk about avoidance in general too.
I’m not going to ask who has it and who doesn’t because a lot of pepple don’t
want to admit it I’ve found out over the years. I assume some of you do and
some of you don’t but there are other things that (?).
This is the way it’s grown in the big commercial fields down in California
and the seed crops in central Oregon. It’s fairly closely planted on kind of
double row of raised beds and the plant spacing makes some difference in the
way white rot acts in the field and to some extent even the diagnosis of it.
So some of the picutres I show you may not be representative of you if you
are widely spacing your crop but the general points I think are still there.
If you want to talk about general production and horticultural aspects of
garlic and varieties we can do that, but I kind of suggest that we fit it in
around the edges, but if you have a burning question about something I’ll try
to answer it. I may not be the very best horticuluturist for many of your
questions, but now that I’ve grown it in test plots for 30 years and I’ve
kind of learned how to do that over those years, and as I’ve gotten into more
varietal aspects in the last 5 years I’ve learned that there are variations
on a theme with different varieties so I’m still kind of learning that so I
may be better than the average gardener but I may not be the very best person
to answer your question.
We won’t go into a lot of the botany of garlic, you probably know as much or
more about it than I do, but you realize that there
s kind of a mother stem plate down here and as cloves form they have there
own stem plate and that’s kind of important with respect to certain diseases.
What we eat tends to be the storage leaf and there’s that clove cover leaf
sheath that wraps around that. And then you have the mother stem plate here
and the daughter stem plate here and they separate eventually and the leaves
hook up here in the middle eventually. That’s a really old slide that I’ve
scanned in that shows you that in a little more colour. I’m going to skip
through some of these slides, I through up some varieties, this talk was
multipurpose so not every slide is going to be of general interest.
But an important message whether you are a gardener or a small commercial
grower or even a big one is that any plant that’s dying out there prematurely
prior to normal senescence late in the season, you should pay attention to
and get out of the field. Now it may not be white rot but while you’re doing
that you can discover whether it’s white rot or not. Lots of things can
kill garlic, or some things can kill garlic, and none of them are going to
do you any good leaving them in the ground. With white rot it’s particularly
important to roque them out, the others it may or may not be as important ot
roque them out, but roqueing, in the process of roqueing them out, your going
to take a closer look at what’s hurting them and at least pick up on whether
it’s white rot or not. And that’s really important if you don’t currently
have white rot or don’t recognize it, to learn to recognize it in the very
earliest stages because it’s a lot easier to control or possibly eradicate
in the early stages than if you let it go.
White rot becomes, if you have more than just a single propagule of the fungus,
and let’s say you’re somewhat generally infested, or even lightly infested,
it can become worse as the season goes on, and it can continue right up until
harvest and in some cases as a post harvest problem. It’s usually a little
bit more unusual to have it as a post harvest issue, but I have a friend
who worked for the U.S. navy in his early days as a person who buys and sells
food for ships and he said they opened up a ship’s hold once of onions and it
was a mass of white rot. And so that can happen but it’s unusual, a little
less unusual in conditions like yours here where your probably harvesting
plants in a little greener stage than if you let them dry down to the point
of extreme dryness like we do in the desert areas of California, Nevada and
Oregon, because moisture will allow the fungus to continue to grow.
In any case it can appear early in the season and it can appear late in the
season and at any time. So if you’re looking, especially if you’re a small
grower you have the ability to walk you field or garden or farm on a regular
basis then you’re way ahead of the game looking for the dead and dying plants.
That’s where the big commercial companies tend to fail because if they have
a hundred acre field, or ten hundred acre fields, they’re not willing to do
that, and put in the time to walk and rogue those fields and so it gets out
of hand easily and quickly.
This is something that’s not in the slide set
(handed out) but I get a lot of questions about bulb mites and frankly there’s
not a really great source of information about bulb mites. If you look on
the internet, like I did on that handout, you can find information but there’s
almost no good pictures of what bulb mites do to plants, just some kind of
half assed pictures I think. Most of them aren’t on garlic, they’re on
narcissus, or day lilies, or grain or something like that. So you have to
read those and synthesize what you can across the board to get a picture of
what bulb mites really are and what they do. This is just a reiteration
of some of those email addresses that I handed out and this is a picture of
some bulb mites and I guess a stylized picture of what they might do to a
bulb. I’m not an expert on bulb mites either and there are hardly any around,
so it’s a discomfitting issue to really get good information on
bulb mites. They are natural inhabitants of soil and they eat a lot of organic
matter but they have the ability to grow onto some kinds of plants and in
their general forging dig into fresh tissue, they particularly like bulbs,
and they particularly like newly planted seeds of grain and seedlings of
grain. Their damage is related to the amount of the time that, or the
population they have and the time they have to work on the plant before
environmental conditions may disfavour them, or until the plant gets up a
head of steam and out grows them. That’s not real satisfying as an
explanation of bulb mites but they’re a simple mite, they only have four legs,
they’re larger than a lot of the other four legged mites, you can see them
with a hand lens, especially in high population they’re pearl like.
The way I think about them in garlic is that some varieties seem to be more
susceptible than others, the California varieties that I tend to work with with
the big industry down there don’t seem to be particularly susceptible.
They’re a little more susceptible if they’re shipping the product overseas
and it stays in storage a long time and if the population is fairly high
on the bulb when it comes into storage. But if you’re pulling your garlic
out green, and it’s taking a long time to dry down, they can act on your crop
during that period of time, and they can continue to act after you plant
your seed back out for a period of time. It’s all poorly defined what that
period of time that really means and it relates to the populations that
you’re dealing with. So the bottom line is it’s best not to have grain in
your rotation that will tend to aggravate them a little bit, other things
seem to disfavour them a little more, they can still probably be a problem,
nevertheless, and there are probably ways to treat them, even organically,
as you are planting your seed back out, probably with a disinfectant of
some kind, like chlorine, I can’t remember if that’s allowed in the U.S.,
I know that it’s allowed(?) in Canada. Garlic can stand a chlorine dip
for probably a few minutes, diluted bleach 1 to 10, probably a diluted
alcohol or even an undiluted alcohol might help. Some of you might even
have your own formula and would share it or know already how to deal with
this, but it can be an issue although there kind of the last thing you
think of. Usually you see some kind of scarring on the cloves under the
leaf sheathes and that scarring is sometimes related to their activity.
That’s all I’m going to say unless you want to talk about it more now or later.
This is another disease which frankly very few people know or think about
because they think it’s normal to some extent. I think that a lot of the
drier areas of the world, like California or Oregon where I work, we tend
to see this surface discoloration of bulbs if they stay damp a little bit
too long in the field. We tend to dry things down in the field rather than
in a shed, so if the soil has more moisture, gets more rainfall or an
irrigation that was not
scheduled you can get a lot more of this discoloration on the seed. We
tend to ignore it on fresh market garlic that could be a disaster, so they
tend to pull up fresh market garlic even in California, even though it’s
dried out, they pull it up earlier than it would be for a seed lot to avoid
this discoloration. It tends to be mostly caused by this fungus
and so it is probably an honest disease although we tend to discount it or
ignore it as more of a post harvest issue. I don’t know what kind of a
problem they cause for you here but if you think it is a problem we can
discuss it but it’s not something that any of us much of an expert on.
In parts of the world where it’s really wet all the way through harvest and
stuff going into storage it can take the cloves down and make them pretty
ugly and ruin them. I don’t know of anywhere that happens in North America
but all reports of this are from Korea, or Brazil, or somewhere so I don’t
know that it’s a big problem but we do have the fungus and presumably in the
right conditions it can take it pretty ugly. This is just a picture of the
fungus, not particularly important for you to see that. And these are some
pictures of it. I think this can start to look like some of the other problems
we get so I am a little uncomfortable saying that all that is Embellisia
but maybe it is.
I’m sorry I actually switched diseases, Embellisia can look a little like
this, this is that is described out of washington just a couple of years ago
called Fusarium proliferatum, and I occasionally see stuff like this out in
the field but I don’t see very much of it. They’ve seen most of this in
the world garlic collection that they made back in the early to mid nineties,
and whether they brought it in, or whether it’s just some varieties are a
bit more susceptible, I’m not so sure because I don’t see a lot of this in
our commercial garlic. If you see a lot of it I don’t think we even know
what to do about it, it’s probably more of a post harvest isssue, proabably
some handling issues about the garlic coming out of the ground. This again
causes bulbs to shrivel, the cloves I showed you earlier they have this
whitish rot, but when they dry out the bulbs just shrivel. It looks a little
like a fusarium problem that I am very familiar with, we essentially
described it a few years back in California in the seed areas, and that’s
Audience member: What would cause that bulb rot?
This one here?
Audience member: Yes.
The previous picture I showed you just progresses from that into this as your
bulbs dry up and shrivel because the fungus is in the cloves and on the
The next fusarium problem is somewhat related. Fusarium fungi are ubiquitous
in soils. This is one that can be a storage problem and is caused by
fusarium roseum. It looks a little like that last fusarium proliferatum
problem but this is a different fusarium and it can range from having no
symptoms at all, to maybe killing one clove to the whole bulb. That’s not
real common to have it flair up really bad in storage but it can happen
and I’ve seen it happen. This is the same fungus, fusarium roseum, earlier
in the season. We see this a little bit every year in central Oregon and
I wouldn’t be surprised if you see this in your garden. You get some leaf
flagging because the fungus is acting down here. It’s essentially killing
the stem plate area and then moving up a little bit and causing this leaf
flagging. It’s not white rot but white rot symptoms up here would look very
siimilar because it’s also killing it down here. So fusarium roseum attacks
right up the stem plate and then it causes this watery beige rot on the lower
part of the plant. That’s pretty diagnostic. I don’t know of anything else
that looks like it except maybe that fusarium proliferatum possibly, but that
ones more very late in the season while this one can occur early in the season
and all the way through. We have actually seen serious field losses to this
but in general it isn’t a serious field problem it’s the occasional plant.
When it first appeared in California I was still a graduate student and
we walked out and saw this field that was going down really hard and we
thought it was white rot and we pulled it up and it wasn’t, it was something
else. That was the first time we’d seen this and it turns out that it’s very
abundantly clove born. In other words it can infect the bulb and cause no
symptoms at all but it can be in those cloves and replanted in the next lot
and it can actually carry over from seedlot to seedlot to seedlot and cause
no symptoms at all for year afte year and then under the right weather
conditions, which we had never fully explained, suddenly turn into an active
rot phase. So what the California industry did was gradually weed out the
seed lots that had this. That took a little bit of effort but now that it’s
generally weeded out all we ever really see is just the occasional plant go
down in the field and it never seems to build back up in the seed lots.
In the early days it had already built up in some of the seedlots and had
become a serious problem. What I would reccommend is, if you’re just seeing
the rare plant go down with this, to ignore it, but if you’re seeing more
of this in your field then you consider getting rid of that seed lot and
buying another seed lot. Sometimes that’s painful to do because you have
a special variety that you like. In general I don’t expect that you’re going
to have a serious problem with this but just be aware that it can flare up
and it is closely associated with seed. It’s also caused by the same fungus
that causes a common grain foot rot in dry land wheat. The strains of the
fungus that attack garlic are specialized, they can attack wheat, but the
ones that are on wheat generally won’t attack garlic, so there seems to be
some special adaptation that’s gotten into the strain that grows on garlic.
It seems to be always there at low levels and although not exactly ignoring
it, we only do something about it if we seem to be getting a lot of it.
Is this something that you think you’ve seen? It’s a judgement call as to
whether you think you’re seeing a lot. If you had a thousand plants and
you saw one then I wouldn’t worry about it, but if you had a thousand plants
and you saw fifty then I would worry about it. That would suggest that
a lot of the other plants would have it in it and could flare up in another
year and kill a lot of your plants. Or it could even take them down in
This is just another close up picture. The red thing now is just a plant
response, even though this fungus is called roseum and it can be red in
culture, the rot itself is this beige watery thing. This is just a plant
response to infection. It’s growing up here and the plant is trying to
fight it off but it’s losing the battle and it turns red in the process.
There are obviously some coloured garlic varieties and so you can have a
natural red in some garlic varieties but in this case that’s not really
natural. This is just that fungus in culture. It is a red fungus in
culture but in the plant it doesn’t turn red so it is confusing.
Now we are going to get into a disease that I assume you have but I haven’t
been up here enough to actually know if you have alot of it. It’s
Botrytis allii, Neck Rot, which may not be a real formal name because there’s
Botrytis Neck Rots on other crops, particularly onions, and that’s a different
species of Botrytis. The disconcertin thing about Botrytis is that it can occur
in very small clumps of three or four plants and that’s one of the things
we look for in white rot is small clusters of plants. Normally Botrytis will
kill just individual plants but if it does occur in two or three then you want
to pull those up and make sure you can tell the difference between Botrytis and
White Rot, and we might spend a little time on that. Again anything that can
hurt the plant here below the ground is just going to result in leaf flagging
or senescent leaves prematurely when the rest of the crop shouldn’t be looking
like that and these are then you need to pull those up and look at them.
It actually can be caused by two different species, Botrytis allii and,
more commonly, Botrytis porri, which are two different species of the related
fungus, and in real wet areas you can find allii as commonly as porri. In
dry areas like where I live porri is the more common one. This, alllii,
to be the one that can cause the Neck Rot on onions. Porri has been found
on onions, Lindsey Dutoit in her surveys of onion fields in Washington has
found that porri is found on onions but it doesn’t seem to cause a problem
on onions it just grows into it.
I’m going to show you a couple of pictures of Botrytis. It has a couple of
characteristics that I think are important. People tend to notice it late
in the season on big plants because it’s more dramatic in a sense, but it
actually caused more damage very early in the season on very small plants.
So it can sneak up on you and hurt a lot of plants before you even think
about looking at them. This Botrytis porri in particular is a cold weather
fungus. It likes it down just above freezing, say between 30 and 50 degrees
Fahrenheit, and so it can actually be causing damage in your garlic patch
in central Oregon where I am in February, even in January if we have a warm
January, although most of our growers won’t even think about going and looking
at their garlic until closer to April, and so it can be doing it’s job in
February – March if we have a wet spring before these guys even think about
spraying for it. What it most commonly does is it forms a spore and the
spore lands near the soil line somewhere, wherever your soil line is, and
it’s probaly up higher than where i drew it here,
I didn’t draw much of a neck on the garlic plants, did I?
In any case it will land near the soil where there is some moisture that will
persist. It likes three things: it likes it cloudy, it likes it wet, and it
likes it cool. So at any time in the spring when it tends to sporulate more
it will land near the neck and if the neck stays moist for long enough it
will infect. We plant our garlic pretty deep in central Oregon because we
can get freezing conditions enough that we lose some garlic sometimes.
So the soil line might have been up here originally on this plant, so it might
infecet there and then it grows down, and it grows down the oldest leaves
and moves in. I’ll show you more pictures. This is a little bit of the mold
here. It’s penetrated into a couple of leaves and then it’s growing down
further, and it’s actually made it all the way down here to the base of the
plant. It’s formed some black sclerotia and these are distiguishable from
white rot sclerotia, which I’ll show you soon, in that they are larger and
formed more like a mouse turd or rat turd. It doesn’t form a lot of these.
It will form some and not every plant will have them but sometimes will.
As it grows down it’s growing in and that’s why it’s worse on small plants
because as it grows in it’s progressivel killing the leaves into the centre
of the plant. Even if it doesn’t kill this plant it will make it unproductive.
So you’ll have plants where it’s penetrated in very far that may survive the
season but they get a really tiny little bulb and so they are essentially
useless. They can actually kill them, and if it doesn’t kill them and they
are still big enough, you can have these sclerotia hang off them and you might
not be able to sell them anyway. So it can be kind of nasty.
Here you see the typical plant response to the infection, this is a lesion
here and this is a lesion here, it’s actually sporulating on that and there’s
a gray, beige sporulation. All these Botrytis species are gray to beige when
they sporulate. The mold itself isn’t usually as fluffy as white rot, but
it can be fluffy in places and when it is it can be a little bit white and
so that’s another reason it can be confused, but usually turns to gray pretty
quickly. These are all lesions on these plants that from the neck infection
are moving down. This one hasn’t turned red but they’re still there. It’s
dirty looking. I usually peel these leaves back. So if I have a plant that’s
getting premature leaf flagging I’ll pull the plant up and peel these leaves
back looking for lesions on the fresh tissue. This one was probably infected
up here weeks ago and now it’s grown down and you can see the active lesions
here. Here some with sclerotia. In the last two years we’ve had a lot of
this in central Oregon and it’s hurt us in some fields pretty badly.
It’s varietal related too. Of the two California varieties we grow, California
early doesn’t get it as much, California late gets it a lot. Yet the worst
field I saw this year was from California early so it can go both.
THis shows you four good plants that I’ve peeled back the oldest leaves
just to show you that there’s nothing wrong with them, they look absolutely
normal. These are a little smaller, you can see the neck diameter is a little
smaller, because the fungus has already killed off
a couple of leaves and stopped some of the good growth. This is why I pulled
them up because these older leaves were beginning to senesce. I already
pulled back the deadest leaves and exposed the fungus activity on those
Any questions? Is this something you see here? I would assume you do
because it likes cool climate conditions and you do get that and you get
enough moisture. It would be worse on heavier soils because it would stay
wetter near that neckline. In the dry desert where I live we can control
it by managing irrigation, but frequently it’s hurt us before the irrigation
even comes on. It can be difficult.
Audience member: It sounds like from what you’re saying that you can distinguish
between white rot and botrytis by the timing.
Not the timing so much, but I will talk about that because it’s an important
distinction to make. You can’t tell it by the leaves, all you’re getting is
dead leaves in both diseases, and you have a hard time telling it by the
clustering because botrytis can cluster a little bit, although white rot
will cluster more.
Audience member: But you’re saying that botrytis will show up in cooler conditions
than white rot.
Well that’s probably true. White rot won’t get active until about 10C, 50F,
botrytis can be active at air temperatures before that. In central Oregon
our white rot symptoms don’t start until late March to early April and
botrytis can be active before that, but botrytis can continue to be active
so there’s a big overlap. What botrytis won’t do is to go down to the
roots so these plants won’t pull up easily. Whereas with White Rot, as we’ll
talk about a little later, it comes up from the roots and ususally by the tme
we’re seeing leaf symptoms there’s almost no roots left and they pull up
pretty easy. That’s a big distinguishing factor. Another is the sclerotia.
One reason I want you to leave today feeling like you can identify white rot
with a hand lens is to know what the sclerotia look like because the
sclerotia between these two fungi look very different and you shouldn’t
be confuse about recognizing them. I don’t have any botrytis to show you here
but the white rot sclerotia a very disctinctive and these are not very
disctinctive. I didn’t have these pictures at the last conference and I’ve
always been a little negligent in having enough botrytis pictures around,
because it’s not a disease that is universal in the world. The only places
that it’s reported much are occasionally in California, and frequently in
Oregon and Washington and I assume up here. Even though it’s not widely
reporte I assume it occurs up here. The earliest reports in the world are
from eastern Europe back in the twenties, and the only place it’s even
mentioned is on leeks in Scandinavia, where it infects in the field in the
fall and then they put that in cold storage and it continues to rot in cold
storage, but it’s a different acting disease in leeks than in garlic and so
you won’t see a lot of information on botrytis around. It’s just here and
Audience member: If you find some, the occasional plant, what should you do?
Well, that’s a question, because in the conventional fields we can spray
for it but they usually don’t spray earlier enough so by the time that gets
down below the ground there’s not much you can do. If the spray is to spray
the foliage near the soil line to protect that infection. I think your
copper sprays could probably do you some good, but they may not be quite
as good as some of the more modern conventional fungicides. So I don’t have
a really clear answer for controlling it if it’s rampant in the season.
I’d say this because I haven’t finished on it yet. I used to think that these
small clusters of plants were where and infection started because it will
sporulate above the ground. That’s how it spreads around the spores get
up in the air. It can also spread from old material from the year before
so there’s a few cultural things you can do to help yourself too, get rid
of old material. Let’s say it’s sporulating on a plant, I used to think
these clusters were from splashing short distances and then they happen.
I’ve had reason to question that this year in that we had a problem in
central Oregon in 2005, the crop that was harvested i 2005 had a serious
botrytis problem. These are seed fields and so we knew that botrytis can
be somewhat seed borne, but I’ve never found more than one out of about
three or four hundred plants, where it was in the seed lot, I mean I’ve never
found a seed lot where it was infested more than about one out of three or
four hundred plants. When I went out to a field this year that was
planted from seed grown in central Oregon last year, where like I say we had
a serious problem in 2005, so some of that seed came back and replanted for
the 2005 2006 crop. These are plants that we pull up out of one field,
and I’m guessing that probably over ten percent had botrytis that was rotting
the (?). That’s a serious loss because you can’t control it, it’s below
ground, there’s no way you’re going to spray down there. So ten percent of
that plant was rotting away by spring from the seed borne infections and it
looked like some of those seed borne infections where they were contacting
neighbouring seed pieces, because we plant fairly close in our seed fields,
were probably spreading from plant to plant below the ground and I think that
some of our clustering in some years might be due to that phenomenon. NOw if
you’re planting your plants wider apart you probably don’t see that, but where
we’re planting close enough that they can be touching we can see it. I think
that clustering may result from that rather than from spore splashing, maybe
Audience member: So what is close and what is wide?
Well in our seed lines we plant 8-10 plants per foot and obviously your just
dropping them from a mechanical seeder so some of them are touching, it’s
an irregular spacing, it’s as regular as possible but still you can have
3 or 4 seed pieces piled up against each other. Where I’m planting my hard
neck garlics by hand I don’t have them that close and so I probably won’t see
that clustering. I don’t think this fungus grows through the soil I think
it has to actually be touching so you probably wouldn’t see that. It is true
that you can have some seed born innoculant and what happens with this is that
I said from before it grows from the neck down, in this case it’s already
down here so it grows up, and then when it gets above the ground those spores
can start flying around on the neighbouring plants, so it can spread from
seed bourne sources. Now the other source it can result from is last years
crop that’s still lying on the ground, and so that’s something you can do,
is make sure you’re not leaving old garlic debris in the field. I can find
it sporulating on old dead plants, I can find it on volunteer garlic, and so
most of you are probably being pretty careful to weed out all the garlic from
a given planting and there’s good reasons to do that, one of them is to reduce
as much of this kind of innoculant as possible. In commercial fields there’s
a lot that’s left in the field and garlic volunteers are a serious problem
in those big commercial fields we deal with. So volunteers are a source of
virus, a source of botrytis, a source of lots of things. So clean cultivation,
no volunteers, gathering up debris all helps. And that’s the same story we
talk about with the control of onions, onion cull piles are a bad source of
botrytis allii which can cause problems with garlic, so if you’ve got onions
you want to get rid of them too. No onion cull piles is a good policy.
Anyway I don’t have a great answer for controlling active epidemic development
in organic systems. Copper sprays would help if you’re comfortable about
putting those on. This is what botrytis can do if it infects really late
and it can be pretty ugly because these big sclerotia in this case can get
really big and they obviously that’s an issue. That’s actually fairly
uncommon we don’t usually see that very often. This is what the sporulation
of botrytis looks like. It normally forms these gray asexual spores on the
old tissue or on the neck, this is on culture plate. It can also forms a
sexual spore which you don’t have to worry about. It essentially does the
same thing. It’s kind of cute actually, a kind of trumpet.
And this is called Neck Rot on onion and it’s caused by one of those two
species of botrytis I was talking about, this is botrytis allii.
In this case it grows on onions leaves and grows down and lodges itself
in the bulb and usually that doesn’t manifest as problem until you store
them. It can occur in the field but it’s more common to have that develop
in storage. If you plant that, like you buy little onion sets from
Holland or somewhere, or if you’re growing them yourself, sometimes the sets
will rot in the field after you plant them. This is a reference point.
It’s probably the most common onion disease in the world and it’s one of the
two species that can attack garlic.
Now I want to discuss a couple of other diseases. I actually don’t have a
good picture of purple blotch on garlic, I don’t know if you see a lot of that
but it wouldn’t surprise me if it occurred in a wet season. Purple Blotch
is an alternaria disease a fungus that again is air born. It’s a good honest
leaf infecting decaying fungus but it likes to grow on dead tissure too.
These pictures are of onions but it would look a lot like this on garlic too.
It’ll form purplish to some extent diamond shaped lesions on the leaves
and they’ll expand and coalesce and when it gets really ugly you’ll lose the
whole leaf, and you can lose a lot of leaves and then production. Again I
don’t know that you have a lot of this, maybe you can tell me, I rarely see
this in the desert areas of central Oregon or California. It’s a more
common problem in the mid west and further east but here you could have
seasons where it’s damp enough to encourge this so it wouldn’t surprise me
if you had this in some years. I haven’t heard anybody raise their hand
and say yeah I’ve got that.
Audience member: If you get a rust, last year being a wet spring, I think a lot of
people had rust and they look similar.
That’s the next picture I was going to show you.
Audience member: What was the last one called again?
The last one’s called Purple Blotch and I don’t have good pictures of it
because I rarely see that in my professional career. It can happen in
California, it has happened in California, I’ve never seen it in California
personally and I’ve been down there a lot to look at their garlic so it’s not
common. I never see it in central Oregon under desert conditions. It likes
humidity and it likes wet leaves so it can be a problem where you have
enough himidity and wetness to encourage it. Now rust on the other hand can
occur, it’s not particularly moisture related. You say you have rust, I was
going to ask whether you did, and whether it’s caused problems or you just
see a little bit of it.
Audience member: I think a lot of people had it last year and were worried about
it causing problems but the problem is keeping it in the field by planting
It’s another one of those issues on organic garlic that I don’t have a great
answer for. Frankly it’s kind of a new disease in western North America.
In California it came in about 1995 or 1997 and it was in the books as a
disease that occurred in California before, but you couldn’t find a single
garlic person who had actually seen it other than it had been seen sometime
in the last fifty years a a curiosity. In c.1995 it wiped out about half the
garlic in California and all of a sudden it got their attention almost put
them out of business. So they quickly registered some fungicides and they’ve
managed it ever since and it’s been around ever since. It’s found in the
Willamette valley of Oregon but not enough that it’s hurting very much.
I don’t know that they’ve sprayed for it but they’ve noticed it. We’ve seen
some up in the Columbia basin between Oregon and Washington. Again very late
in the season you see some of these red or orange pustules but not enough
to spray for it. Theoretically I’d say it could come up here because it likes
mild growing conditions. The year that they had it so bad in California was
a real mild year for the Central Valley, wasn’t real hot like normal, and it
really flared up badly. Where we’ve seen it since is in the spring when it’s
milder. In the Willamette Valley where it’s always pretty mild it’s never
flared up really bad but it has the potential to do so and I think the same
potential exists here. Late in the season instead of being orange it will turn
black and get that diamond shape. I honestly don’t have a great program for it
in organic production to manage it. If you’re seeing it I would get rid
of those leaves though. It’s probably just a good idea to minimize the
potential for it’s spread. You may not eradicate it, and you may not in a
year if it was really going to blow up in an epidemic, you may not get rid of
it by doing that but you’re going to at least keep it down and put your best
foot forward about it having become an issue. I don’t think I would
necessarily pull out you little plants, I think I would just pick off leaves
where you see lesions and if every leaf on the plant has it then maybe get
rid of the plant then. Again something like copper sprays will help, they may
not control it as well as some of the more modern fungicides but they
probably will help.
Are you routinely putting on sprays on garlic? I wouldn’t think so.
Audience member: Just to comment I use aerated compost tea. I don’t know
if there has been any work done to see if it helps.
I’m sure there’s been those done but I can’t tell whether you’re helping
control it or not.
Audience member: My sense is that it is. Any of the leaf borne diseases.
There’s a lot of work being done on compost teas now to prove their merit
and work done by research scientists, like me although I’m not doing it,
and so I think you’re going to see a lot more verification of that kind of
thing come out in the scientific literature. Actually you guys are way
ahead of the scientists now in your use of those products and so we’re still
trying to prove to ourselves that they work. It wouldn’t surprise me if ther
were some concoctions that do work, I just don’t have anyting definitive in
my own work that I can show you. If you have really optimal conditions for
rust even the best fungicides don’t control it fully so I wouldn’t expect
compost teas to do any better. Right now I don’t think we have optimum
conditions for this disease in the more northern areas of the west coast
and it’s been more of a California problem today.
Audience member: I was wondering I didn’t catch the name of the rust.
Well I didn’t give it to you. It’s a Puccinia, it’s related to the rusts
that go into wheat and other things, but most of the time we don’t toss out
rust names because they’re all just rust. They are very specialized, I should
tell you at least that, the rusts that you have on roses, or anything else
is not going to go to garlic, and the one that’s on garlic is not going to go
to them so there’s thousands of rusts in the world and most of them are very
specialized to the crop that you find it on. There is one that goes to
asparagus that’s been found on onions, but it’s not the same rust and this
garlic rust also goes to onions but not as badly. So if you have an onion
that has rust on it it could be the asparagus one or this one. I couldn’t
tell you which without sending it to a specialist myself. If it goes to
garlic it could probably go to onions a little bit but it’s really a garlic
problem, or we think of it as a garlic problem. I don’t know of any onion
fields that have been hammered by it although they’ve found it on.
I don’t know how much time I’ve spent on other things but we’ll talk about
white rot for the rest of the time other than we’ll go back and talk about
botrytis distinctions a little bit later. Actually I have a couple of more
slides of nematode on garlic. Nematode is the other really nasty disease of
garlic. White rot is the nastiest and nematode comes close. If you have a
serious nematode problem what you see is all the garlic goes down and that’s
what can happen with a real serious case of white rot. This is at least
20 acres, it could have been as many as forty or fify, and every plant was
going down to nematodes. This is a commercial field back in California when
I was a graduate student. This guy has since retired so this is about thirty
years ago. So it can be a serious problem. With nematode you get the leaf
death like with anything that’s hurting the plant down in this area and when
you pull it out, usually something happens a little later in the season,
like in the last month or so, the roots are relatively intact, the leaf
sheathes are real punky and pithy, they’re usually bloated looking, and they
tend to separate from the stem plate and that’s why the leaves are dying,
because they’re going through this separation. THis is caused by a nematode
called Ditylenchus dipsaci. It’s not your normal soil born nematode, it
prefers to live in the plant and so it can be seed born, carried through
from plant to plant. It’s one of the things that dictates what we do in the
big California, Nevada, Oregon commercial seed industry. They’re dealing
with real high volume and quality control is poor at times and this thing will
build up in the seed lot over two or three years and you’ll never see a plant
that has a symptom and then all of a sudden it spills over the economic
threshold in the plant and they all go over, the whole field. THey have
serious programs to prevent that from happening. I have seen it happen with
small growers too. I’ll give you an example. I was in Australia in 1997
at an international allium conference and they had a small garlic industry
of boutique growers of 1 to 2 acres that had built up all around the southern
Australian tier from Melbourne to Adelaide, there’s probably 30 to 50
growers and they were networked with marketing and so it was a emerging
industry and a big deal. They were all sharing seed and they had no seed
quality control in their program and at that conference a lady field person
walked in with some plants that looked just like this to me and said
“I’ve got a field with maybe 1 percent of the plants are looking like this”
and I looked at that and I’ve only seen nematode as a serious problem about
4 or 5 times in my life as a career, because we worry about it so much,
while they don’t worry about it at all, and I said “Well it looks at lot
like nematode, run that down to a nematologist and have them do an assay on
it” and I called over the guy from the previous picture, that I told you was
retired, and said what’s this look like to you? He said “Well looks like
nemetode to me” He emailed me a week later when I was back in he States
and he said
that it was full of Ditylenchus and every one of those farmers went out of
business that year. He emailed me a week later that they had found it in
that field and that they had done assays from other fields, and it was in all
those fields, and a year later I found out from some of my friends that all
those garlic growers had gone out of business that year, 30 or 40 of them in
one year. I’ve seen that happen one other time in Oregon, a bunch of
growers around Eugene, organic growers, bought a seed lot from one of the
major seed companies from California, and they asked them to hot water
treat it, which was one of the standard treatments gor gettin rid or this
nematode at the time, and the seed company didn’t hear them right and they
said well they’re organic they don’t want anything done to it, and they
sold this load, all the organic growers planted it out and they all got it.
So it’s a problem that’s controlled by rotation, the nematodes will live in
the soil for another three years after they come out of a plant like this
and get into the soil, but they die off, they don’t like living free in the
soil very long. So all of our rotations in Oregon are 4 to 5 year rotations
to help prevent this from perpetuating. All the seed is either hot water
treated, less of it’s hot water treated now than ten years ago, what they
have now are plant sampling programs. They do what they do with seed potatoes.
They’ll grow out 3 or 4 generations as seed increase and they’ll assay from
each of those generations and if they find it in one of those increased
generations then they kick it out and it goes commercial. That takes care
of it from building up in seed lots. So you can actually assay the plants
in earlier stages before you see disease symptoms and detect it building up in
those plants. But it has to have a fairly high population in the plant before
it does this. So in California they have a plant come out of a test tube for
virus control and they’ll put it into a nuclear(?) planting stock and they’ll
build it up over a couple of years and they’ll get a nuclear field and they’ll
start assaying after nematodes. Usually they don’t find any and they grow
it out the seed increases per year sampling again for nematodes…(?)…go like
that and eventually that spills out into a commercial field and then it goes
to market. But if say in the year before it’s going to plant a commercial field
they find nematodes in it then they’ll take it to market right that year and
flush it out of the system. So most of the companies have converted over to
doing that rather than hot water treating because hot water treating is
difficult to do effectively, you can have a chance of cooking the bulbs and the
seed (?) and so there were some other issues coming from the EPA about
disposal of water and those kinds of things.
Audience member: We have certification of seed potatoes, is there such a
thing as certification of garlic seed?
Yes and no. It’s not as tight as it is with potatoes, and I’m talking about
California, Oregon, Nevada, and Washington. Nevada has a …(?)…
program. They sample every garlic field for both white rot and nematodes
and manage it as a state agency. In California they sample for nematodes
on a voluntary basis, the company asks them to sample. Most of those
companies are not doing their own nematode assays so they used the State
service and that flush out program I was describing. In Oregon it’s pretty
much similar, we have a white rot certification but the nematode is voluntary.
So a grower or contracting seed company has to ask for that to be done.
Some of it’s done and some of it isn’t, companies have a pretty good handle
on whether they have suspect seed lots. Having said that one of the smaller
companies about 4 or 5 years ago, as a cost saving measure, got rid of their
nematode program, they hadn’t seen nematodes in 10 years so they said that
“Well we don’t have them anymore” but about 2 years later they lost a bunch
of seed lots because they stopped looking. It tends to be, like white rot,
more of a problem with bigger operations because their quality control tends
to be low in managing seed lots, there’s always some slippage, they get
dirty boxes, they skip a year looking, those kinds of things. Now you as a
smaller grower, I see most of you …(?)…acres of garlic, as a smaller
grower your risks are that you could bring this in from a seed lot that you
don’t know a lot about. You purchase a seed lot from somebody, or you’re
sharing seed back and forth, like in that Australian example. As long as
it’s clean your risks are zero, if it’s dirty then the clock starts ticking
on increasing that seed lot and you can get blown out of the water 5 years
down the line. So in my own program that I’m starting up myself I’ll probably
have my sample of plants assayed for nematodes every 2 or 3 years just as a
safety measure. If I see nematodes in them I would probably go in and sample
each variety at that point, and find out if I have it in one seed lot, and
maybe get rid of that one and start over with that variety. It’s something
you can ignore and get away with for maybe a whole lifetime, but it’s also
something that can put you out of business, and so there’s a certain amount
of sampling that can make you feel better about your program if you do it
once in awhile. If you’re really small maybe don’t worry about it. If you
just a gardener, strictly a gardener, maybe don’t worry about it. If you’re
in a commercial enterprise I think you owe it to yourself to worry about it
a little bit. At least to sample once in awhile. So if I have 10,000 plants
out there I’ll probably sample about 50 plants across all varieties and send
that in to the lab, if they come back and they say “Yeah we found some
Ditylenchus in there” then I’ll probably go back and sample each variety,
10 or 20 plants across the whole variety and then try and make some decisions
about whether some of those varieties have a problem. It’s not going to be
much of a soil problem as long as you’re rotating. If you’re not rotating and
you’re planting garlic back into the same piece of ground every year then
it could become a problem out of the soil itself and so you have a rotational
issue there too. It can go to onions. In onions it’s ususally more rare
because most onions are planted from seed and it won’t pass through a true
seed. If you’re putting onions where you had garlic before, or if you’re
planting onions from sets and then growing your own transplants year after
year then you could possibly get it onto onions too.
Audience member: What do you see as the ideal rotation just from the safety
Let me talk about that a little bit later when I talk about white rot because
there’s some issues in the management of white rot that relate to crop
rotation. To control this a 4 year rotation is smart and 3 years is probably
good enough, 5 is probably more than you need. THe 4 year timeline is the
basis that the big industry uses as it’s standard for rotating…(?), rarely
they’ll put a field on a three year basis. And you have to worry about
volunteers in that case too so three years with no volunteers.
I’m not going to talk very long about viruses because viruses are in most
garlic and most of you are living with viruses already, your OK with them
in a sense. If you didn’t have viruses you would have bigger bulbs, but
there’s very little other that the virus is going to do in term of plant
health. Now there are diseases of some crops that will kill plants or
disfigure them but the garlic viruses all just make a smaller plant. Most
of you have those virses in there now and ignore them. I’ve been going
through a program of …(?)… of my garlic and as expected about a 30 or
40 % bulb weight increase I’m get…(?)…Some varieties may not respond
to the viruses as much, some of you have huge cloves, bulbs, already, so
maybe they’re very tolerant of some of those viruses, but they do exist
and it’s a pain to get rid of them, and if you’re in an area with a lot
of aphids they’re going to come back in anyway. So maybe just don’t
worry about them as a small grower. The most common thing you see is a
colour inconsistency, an off green to yellow look, it can be subtle.
On this slide these were some virus free plants compared to the others, or
these were produce from these by making them virus free. You can see a
big growth difference there in that variety. So that’s all I’m going to say
about viruses, if you want to talk about viruses we’ll have to do that later.
I will mention one more virus this is one that’s become very prominent in
the pacific northwest in the last 3 or 4 years: Iris yellow spot virus on
onions. On seed onions it causes these real distinctive diamond shaped
lesions. On fresh market onions it’s not quite as distinctive. It’s
spread by thrips. This was an onion the previous year and the year before
and this was a seed crop so this was coming out of onions and overlapped
with seedlings that were grown right next to it. Thrips moved from this
field into this one and these plants have all gone down to Iris yellow spot.
Again this is just onions. For 3 or 4 years we’ve been wondering whether
garlic could get Iris yellow spot. The answer is apparently yes but it’s
not very likely that you’re ever going to see a symptom of it. The only
place it’s been reported in the field is from a small island down in the
Indian Ocean where you have to have hellacious thrip population. Thrips
love onions, you probably now that, but they don’t like garlic very much.
You have to have a really high population to get on the garlic before it
will spread anything to that garlic and it’s unlikely you’re ever going ot
see a symptom on garlic anyway. So it’s something I won’t worry about but
if you have onions this could be a serious problem.
The problems we’ve talked about so far the ones I think are most important
are botrytis and bulb nematode. Bulb nematode because it can be something
that can build up unseen and then knock you out, and botrytis because in
some years it
can just cause a lot of damage in itself.
Both of them can be, just in a superficial sense, be mistaken for white rot
because they can kill leaves.
White Rot is a fungus called Sclerotium Cepivorum. It’s a sterile fungus
meaning it doesn’t have a sexual stage. In a taxonomic sense that’s
confusing. I’ve even had mycologists come up to me and tell me it’s related
to the mushroom type fungi but it’s not it’s related to the sclerotinia(?),
botrytis and those types of fungi which are very very different kinds of
fungi. The problem taxonomically is that this name just refers to a sterile
fungus,… sclerotia…most of the fungi that do that are mushroom type
fungi, but this is not a mushroom type fungus.
I don’t know if you see sclerotinia on potatoes and some of your other
vegetable crops. It can be a serious disease issue. It forms a sclerotium
but it acts like a ..(?).. it tends to blow around the spore… and kill
leaves and stems. There are forms of sclerotinia where the sclerotium
infects directly underground. Lettuce has a common probem with that in
California. So it can actually go both ways on some crops.
The white rot fungus is more of a degenerate type of fungus it has no spores
or function, and so it only gets around in life by being carried around
as these little black sclerotia. They’re roughly poppy seed size or maybe
a little smaller. It can also be carried around as active mold inside a plant.
Some of you have seen the white rot fungus under the scopes. There’s three
plants here, one just has a piece of the stem and the dead leaf hanging off
and that’s where you’ll see the sclerotia.
I’d like to use this picture, it’s a real old picture, this is from back
when I was a graduate student in 1975. This is a field in California that
was planted in garlic from this road to this creek and to this road, and
this is all dying from white rot, and this actually died form white rot
offset in time a couple of weeks later. And this was mostly clean with
a few scattered plants that came down with white rot. It’s probably a 30
acre field. This farmer knew he had had white rot here 10 years earlier,
and in his mind he thought in 10 years it must have gone away by then.
Well it hadn’t obviously because these plants were all dying very early
as soon as they were coming out of the ground in March of this year they
were dying so it was probably active even during the winter. He told us
that there used to be a roadway here and that he used to plant this field,
in the previous crop of garlic was here and here, and there was a roadway
here and he reconfigured things for some reason. So it gave us a chance to
look at the soil populations here, that would have probably done the same
thing here, and here which was very very light, actually couldn’t find
the fungus here even though there were a couple of plants going down.
He had probably moved a few sclerotia over here with planting other things
over the years but there was so few that you couldn’t find them. Here we
found a number which later on which in my research program indicated he
could have expected to lose all those plants. It was a number much lower
than at the time they thought would be that damaging. At the time people
thought white rot was primarily a disease that acted right near the stem
plate and directly affected bulbs. They didn’t know that it had a life in
the root system. To get this much loss people would have thought that you
needed a thousand times more there than he actually had. We figured out
in a few years that it’s a disease that can cause a lot of loss from very
low populations. I’ll show you some of the reasons why.
This is a field is central Oregon and these are seed onions, and this follows
a garlic crop from about 5 years earlier that had a little bit of white rot.
Each of these patches was where a plant or two had died in that previous
garlic crop. So you can see that the sclerotia produced on those individual
plants had been tilled back and forth so that they were spread out from a
single focus point into a bigger area, maybe 4 or 5 of these tables put
together. You can see that it starts slow but it’s incessant so a lot of
sclerotia in a small patch killed all those plants. Then you can find
individual plants where individual sclerotia moved off from that patch into
other parts of the field. Seed onions are actually a bigger risk than
garlic because the crop is in the ground for about 13 months. It’s not a
risk of getting into the onion seed itself because it doesn’t go above
ground, but in terms of killing plants it’s a bigger risk. In central
Oregon the temperatures are good enough that the fungus just keeps on
growing moving from plant to plant for a long period of time and with
onions that’s just a longer period than with garlic.
This is another garlic field in central Oregon back in 1990 or so and this
is just one big patch of garlic that’s all dying. This is in early May of
that year. That’s pretty dramatic and when you walk through that field
you can see some dying plants almost every step you take along those rows
so the whole field was essentially dying at that point it’s just that these
were dying earlier and the rest of the field was catching up to it later.
You literally couldn’t take a step in this field without finding another
cluster of plants going down. To have that occur at a seed area was a huge
blow because that field had to have had white rot at least twice before.
At this time in their thinking in central Oregon if a field ever had white
rot, even a single plant, it was quarantined from ever being planted in
garlic again. So to have slipped through our system twice was a big blow.
We actually flooded this field for a year starting about a week after this
picture was taken. It actually worked. It killed almost all the sclerotia.
We dyked the field up around there and flooded it from May to November and
white rot doesn’t like it wet like that, that long. I failed to mention
that flooding is something that you can actually do. It’s heroic but you
could actually do it in you home garden. If you dyked up the area that had
white rot and flooded it for essentially all season and even into the winter
if you could, you would probably do as well as if you had methyl bromided
that field, probably kill over 99% of the sclerotia. You might not kill them
in the dyke itself or outside the dyke, but you could take them back to the
point where you could try to eliminate them in the future by some other things
that we’re going to talk about.
I shown you these pictures to show you, if you’ve never seen white rot before,
that it can really get bad, but it takes several years to build up.
Audience member: Would flooding in the winter be adequate? because it’s a lot
easier to flood in the winter.
The answer is basically no. Actually the Canadians up in the Ontario area
and here in B.C. did some research on that, and it’s published research,
and it kills about half the sclerotia by winter flooding and I’ll show you
later why that’s not really enough. All these fungi over-reproduce they
produce a thousand or a 100 thousand times more than they really need to do
the job. So when you’re talking about a 100 thousand killing 50% is like
doing nothing almost. So the summer flooding, when things are more
biologically active was much more powerful and it killed about 99.9%.
We’ve done research, it isn’t published yet we just got the last data this
year, down in Klamath Falls Oregon, acutally Tooly(?) Lake California, just
on the other side of the California border, in areas slightly colder than
central Oregon showing that two years of flooding will actually irradicate
it. But that’s pretty heroic and I don’t know of any farmer that can do that
but you might be able to do it in some of your situations.
This is that same field and this is a little better image of what’s happening
away from these patches. You can see that here’s a cluster of dead plants,
here’s another and here’s another, this is essentially a step apart from
each other and this was what was happening throughout the field so this was
a disaster. So when I talk about clusters of plants dying that’s a
characteristic of white rot in thicker plantings. Now some of you I know,
as I was talking to Chris and a few others, are planting much more widely
spaced, and you will not see the dramatic clusters of plants go down that
I’m describing, but if you have them even 2 or 3 or 4 inches apart you’ll
still see them go down in a cluster. If you have them a foot apart you
might not see that clustering and I’ll show you why. The plants in the
centre of this cluster die first and the ones further out are just coming
down and the ones furthest out are showing leaf flagging. This one’s
escaped for some reason but it will die eventually. If you pull those
up these are all dead and they’ll have very prominent black sclerotia hanging
all over the remnant of that plant. As you come further out you’ll have
plants that look a little more like these, they’ll have tufts of white rot,
of white mold, which is where the thing gets its name obviously, and some
sclerotia embedded in that white mold. If you go further out yet the fungus
is just beginning to grow on the upper root systems of the plants furthest out.
So when we talk about roguing, getting rid of white rot by roguing out plants
you need to rogue not only the one that’s showing the systems you need to
rogue out the plants away from that also because it’s growing onto those and
they’re going to go down or they rot so late in the season that you might
not notice it and there will be a lot of sclerotia produce on them.
And not only do you need to rogue them you need to dig out that soil where the
sclerotia have fallen of the infected plant into the soil. A serious
roguing program is like taking a plastic bag out there and flagging it’s
position in the field and pulling up all the plants, in this case where
the plants are planted pretty close apart, pull up at least a foot or two
feet away from the centre of this cluster, and get all those plants out of
there, and then dig the soil down for probably six or eight inches and a
foot away from that cluster and burn that soil or at least get it into a
Audience member: Will proper composting kill the sclerotia?
The short answer is no the long answer is I don’t know how long it would take.
I know they survive at least some composting but I really don’t know the
answer, there’s a temperature relationship in there that probably makes a
difference but I can’t tell you.
Audience member: Is it known at what temperature the sclerotia will die?
Not really. Have you heard of soil solarization?
Audience member: Yes.
Solarization can kill white rot,but they can be deeper than the temperature
will penetrate and so they might survive below the solarization level.
There’s a temperature time dosage response that I can’t give you. I know
what it is for hot water. I don’t know what it is for a compost heap.
What we’re worried about with a compost heap is that it’s never perfect,
you going to have edge effects. If you dumped all these plants and/or dirt
into your compost heap some of the stuff is going to spill off to the side
where it’s not going to get full affected. With white rot you need to get
it all if you can. So I would kill it somehow in other ways first, it can
be as simple as putting it in a clear plastic bag out in the sun for a month,
that will solarize them, and probably the dirt that you pull out also, or
you can put it into an incinerator and burn, or you can get it into a landfill
that’s never going to be opened up and bury it, but to just stick it
directly into a compost heap I wouldn’t feel comfortable that you were being
efficient enough. You might kill 80% of them, I don’t know, but 10% could
come back and bight you. They will pass through animal digestive systems.
It’r real common to have them eat culled onions in some parts of the world
and crap them out on the next field. And so they can survive that too.
This is a similar patch in onions. It’s maybe not quite as distinctive…
the plants are planted pretty close together. Here you see the white mold,
we excavated some soil away from the plants that were going down. The soil
line is actually up here so the fungus has actually grown up into this
area. I don’t know how deep you plant your garlic in this part of the world,
2 inches? shallower? In central Oregon we are starting
plant them 3 inches deep because
of winter worries which is way deep compared to most people. We used to plant
about an inch and a half. In any case anything that’s below the ground the
fungus can grow up to that point. The dark charcoal areas here are patches
of sclerotia that are forming in those white moldy areas. You can see the
white rot on the roots. This root is particularly showing it. And growing out
into the soil a little bit here. You see some roots that are seemingly OK
and then some roots down here that are pretty involved, the stem plate of the
thing would be about right here and most of these roots have been rotted off.
Audience member: So does garlic form a mycorhizal?
No. Well OK I thought you meant with white rot. Onions are very mycorhizal
but I can’t remember if garlic is or not.
Audience member: Because that might offer some protection.
It doesn’t for onions. White rot is responsive to things in the soil, other
fungi and bacteria and I can explain that a little bit more, but I don’t know
of any competitor or antagonist or parasite that can control it. They’re there
and they probably have an affect on white rot but it’s so small that it’s not
I’ve had people give me the equivalent of some compost teas that I’ve put in at
planting and irrigated on, and in a couple of cases I got a little bit less
percent white rot, in a couple of cases I got more, and I think when I got
it could either be from a bigger root system, or there’s more white rot
to jump on the roots, or it could be from antagonizing the antagonists
that preyed on white rot, and white rot just goes through better. I’ve had
both experiences. And even when there was a slight beneficial effect it went
from being a 70% loss to a 50% loss but that’s still not good enough.
In any case I’ll come back to some of these themes as we go along.
This shows you a little bit more of that white mold. On those plants you’ll
see some of it, maybe not quite as much white, and not quite as much of the
sclerotia showing throught up here.
This looks a little more like the plant over here. This is an onion plant.
Onions tend to get a little less of the white mold. You might tend to find
the fungus more to one side, or you might find other fungi overgrowing the
system, green fungus, trichodermus and other things that are parasitising the
white rot. So onions are a dirtier system to detect the white fluffy mold
and sclerotia, but it you look and you look a several plants you usually find
the sclerotia in any case. Again the roots are missing because it’s killed
most of those off. From where we got these plants here this looks a little
more like this and I suspect that there’s a lot of microbiological activity
in the soil and so it’s probably holding back the white rot from doing it’s
full potential damage on those bulbs. So that’s good in the sense that it’s
good soil but it’s not enough to keep the white rot from still doing that
plant in. What I’m trying to say is that it’s usually a little bit easier
to diagnose on garlic than on onions but you ought to be able to do it on
This is actually an onion volunteer the following spring, and between what
started the previous year and what was continuing on that spring you can see
the solid mass of sclerotia on that onion, and a few sclerotia in these roots
although you can’t really see them very well in this picture. So again they’re
going to fall into the soil waiting passively until they are moved around.
This is still worth roguing out. In other words if you had taken that out of
the field you’re not putting that back into the soil. One of the principles
we’re looking at here. We can assay soil and try to measure the population of
white rot propagules, these sclerotia, slerotia is just a latin term that means
seed-like, I think, they’re not really seed they’re just similar in size to
some small seeds. We’ve taken soil sieves and sized out the fraction of soil
that is the same size as these slerotia, so there are some other organic and
rocks and things that are that size, and this is a lot. If you can find one
per litre of soil that’s enough to cause serious problems. If this a litre
of soil and you find a hundred like this that’ll cause you a hundred times
more, about a hundred per cent loss.
This one is germinating. That’s really the reason to show that to you.
And when these things are near to a root of an alium plant they want to
germinate. I’ll keep coming back to this as a them too, if this fungus has
an achilles heal it is that it’s terribly responsive to the stimulus in
onions and garlic. The same things that you taste and smell turn this
fungus on to germinate, to the point that every time there’s an incident of
white rot, as long as you’ve waited a couple of years, every single sclerotia
that’s anywhere near an alium root will germinate in your fields.
That’s a pretty powerful statement, and it’s not true of a lot of fungi.
I told you before that these things over reproduce themselves, they’ll produce
a hundred, or a thousand, or a hundred thousand times more than they take
to kill all these plants, but if every single one of them germinates then the
clock starts over evey time this disease recycles. So you’ve got a chance
in a sense to get rid of them at that moment in time, and I’ll talk about
that, by trying to trick the fungus into growing when onions and garlic are
not in the ground, by applying those stimulants to your garden and watering
those things in artificially. Now having said that there’s always a few
that escape on the edge of your garden or deep down in the soil that didn’t
get the stimulant and so there’s maybe a few that you’ve missed in the process.
Hopefully those are a few that you can live with or that over time you can
pick up maybe the next time around.
After it germinates, it’s back here somewhere, it’s about this big, it grows
out about a centimeter of two away from itself and it can affect a root that
far away. It has a very limited capacity to grow through soil, this is about
it’s extent, it can grow about a centimeter away from the sclerotium or
root and after that it’s unable to compete with other things in the soil
and it has to find a root or a bulb to grow on to continue to grow.
Audience member: So it just grows out randomly?
Yes, pretty much. I don’t think it’s differentiating a gradient of the
stimulus, so it will grow out in a circle and infect a root within that
centimeter. That’s what it’s doing here, it’s growing out from here and
infecting this root. It’s kind of like lighting a fuse at that point in
that it will grow up that root. This is against a glass box so the roots
are not growing normally, but it will grow away from that root also about
a centimeter and infect the next root over. So the picture on the cover
of your book and that I’ll probably show you again along the way is like
this. If you have a sclerotium here in the soil and it’s a centimeter
away from that root, and it can grow over and infect that root, then it’s
like lighting a fuse, it just grows up that root and it will kill that bulb.
Unfortunately it also can grow over here and infect that root, and it’ll
cross over as long as that root stays intact and it’ll go like this. So
one sclerotium can take out a cluster of plants as I was trying to tell you
earlier. The one that is the closest usually the leaves will flag first
and die, but there’s a time delay from the time it takes to grow up here,
from a foot down it might take 8 weeks, from an inch down it might just
take a week. So it depends where the slerotium infects and those kind of
things. Once it gets up here where the roots are really tightly clustered
it’s usually living amongst all the roots here and that’s why when you see
the leaf flagging all the roots are pretty well pruned off anyway.
Audience member: How deep have you found the sclerotia in soil?
You can find them as deep as you till them. They’re not going to grown
down from that point much, maybe just a little bit, I’ve only ever seen
them grow up as far as a foot though so if you till them 2 feet deep then
I think that the one’s that are effective are in the top foot, but that’s
still pretty deep though.
So there’s a time delay to them moving up and there’s a time delay to them
moving sideways. That’s why these clusters tend to expand and you get these
dead one’s in the middle and progressively later infections further out.
Plant spacing makes a big difference. If you don’t have a plant here and
you have fewer roots then it slows things down. Some of you are planting,
you said as much as 10 inches apart in some cases?
Audience member: Even 12.
That is probably enough to partially break this cycle. My experience with
seed onions that have been bulk planted, and in a few cases of garlic, I’ve
only seen things spaced out as wide as 4 or 5 inches, and it definitely
reduces the size of these clusters that can develop because it slows this
process down. If you’re pulling them out to 10 or 12 inches you may not see
clustering at all, although it would be maybe just 2 or 3 plants possibly.
On the other hand you may have a real high population so if you have a high
population of these things it won’t matter how far apart you’re spacing them
because they are all going to death from direct infection rather that from
crossing over onto neighouring plant. So there’s all these different things
going on with respect to timing and population.
This is another glass walled box. This was a single sclerotium that started
here and these roots don’t quite grow normally. You can see it tracing where
the sclerotium went and this is another illustration of it moving up and
down. Garlic roots will probably grow almost a foot laterally, and another
inch or two below the stem plate, so even at 10 or 12 inches you can
get some clustering but it would be much smaller clusters.
This is just to show you again that it’s really a root disease to start with.
This was a high population in here so I don’t know how many different
infections were happening but all the roots are essentially missing in that
This shows you some diagrams of people who have described garlic root systems.
This is probably a month or 6 weeks after planting in the fall, you can see
a lot of them go pretty well sideways. This is probably a pretty full root
system pretty close to bulbing, again these roots are a foot and you can see
depending on how you space these plants the effect that you’re getting with
this clustering phemomenon.
Audience member: What about 5 feet apart?
Well I think at 10 to 12 inches you’re going to not see much clustering,
because there’s big time delay the further it has to go. I know that the
way we plant them in California and Oregon you can get a cluster of 2 feet
of plants that go down.
This is some work from way back where we actually infested soil at a research
farm down at Davis with different population levels about 8 inches deep.
At high population levels the plants died very early and at very low population
levels we got later death and more events of clustering. I’ll show you some
of that in a second.
There may have been no sclerotia here and there were probably a lot here, and
here there might have been only 3 or 4 sclerotia that does that, that we’re
losing most of the plants.
I’m belabouring this more than I need to maybe, but I wanted to impress upon
you what’s happening. This is an onion seed or garlic clove and these are
sclerotia and obviously for a seedling there’s not many roots to infect so
usually the fungus doesn’t get an early start unless it gets lucky because the
root has to grow pretty close to that to get infected. As you get more and
more roots that’s more likely to happen and you get this phenonomenon that
we’re talking about. So the thing just gets worse as the season goes on
with more roots and more time to grow towards the plant. You’re unlucky if
you lose a seedling. It’s surprising if you don’t lose a plant later in the
year if you have any sclerotia there at all.This just shows that primary and
I want to talk a little bit about temperature. Here it’s not going to influence
you as much as it would in a hot area. White rot is another cold weather
fungus. It doesn’t like it hot. Above 70 Fahrenheit, or about 20-22 C, it
stops and won’t grow at temperatures above that. You have a stratification
of soil temperatures as the season progresses, in a hot soil, we were talking
about mulch earlier, this might be an effect of mulch to keep things cooler.
In an area where the soil can heat up on the surface that can keep white rot
from reaching the bulb. Say if the soil temperature below the stem plate
reaches 22 C or 70 Fahrenheit or so, the fungus will just grow up to that
point and stop. I might progress on the root system below that point but
it won’t penetrate that temperature layer. We’ve seen this in hot areas that
white rot is simply a non-issue as a disease in an area where onions are
spring planted and fall harvested, like Boise Idaho, and the California
desert. You might have white rot active below here, but the soil always too
hot, by the time there’s a root system for it to jump on for it to get up
to those bulbs. It’s best if you’re planting an onion seed shallow.
When I was in Egypt a year and a half ago, they don’t get white rot on
garlic at all hardly, because they plant garlic right on the surface of the
soil even though it’s a winter crop it’s too hot. The plant onions year
round in one form or another and they only see white rot really late in
the winter because it’s a hot country. What they do is they transplant
those onions so the stem plate of those onions are 7 1/2 cm deep and even
in Egypt at 7 1/2 cm it’s cool enough for white rot. So they get that plate
down here where the temperature is suitable.
In central Oregon where it’s cool and in B.C. where it’s cool you’re not
going to experience this much. It’s probably too cool here year round for
it ever to be prohibitive to white rot. Now I might be wrong if you had
a black soil that isn’t mulched much then maybe it could heat up and if
you’re planting shallow maybe you won’t get white rot, but my guess is
that’s not going to be a factor in this part of the world. It can be a
limiting factor in some parts of the world. In Boise Idaho if you grow
seed onion you plant that in the fall, it overwinters, the temperature
barrier never develops and you can have a field that goes down really bad
to white rot. But if you spring plant it and fall harvest it’s too hot,
so within a region you can have seasons that affect white rot. Around
here I don’t think that’s going to affect you too much.
It also means however that you can do this stimulant application program at
any time of the year whereas in those hot areas that won’t work when it’s too
hot because the fungus won’t respond, it’s going to go dormant, at least in
the shallow part of that soil.
This is just a summary slide, it’s like the slide on the cover of your book
showing you that whole story. Plant spacing makes a difference, planting
depth makes a difference, particularly if you’re in an area where the soil
heats up in the amount of white rot that you’re going to get, especially
in the amount of clustering that you’re going to see or not see. If you
have a high population you’re not going to see clustering you’re just going
to see everything die. Remember that patch from that field that we flooded,
an acre size patch, all those plants were probably being multiply infected,
you had each plant being infected about a hundred times. One was enough to
kill it but each root system was probably being affected massively, so they
all die and they all die very early in those hot spots.
This shows you a summary of that. If you have a high population per litre
of soil that’s a lot of sclerotia they all just die essentially just coming
out of the ground in spring emergence. This is spring emergence here, down
in Davis California, essentially in these really high populations all the
plants are dying as they emerge and that’s what’s happening in those hot
spots. At progressively lower populations you get most of your losses from
plant to plant spread rather than from multiple infections and so losses
occur later in the season because if the only sclerotia you have there is
12 inches down it doesn’t show up until the day before you harvest. You
don’t lose very much but it’s also easier to miss. If your leaves are already
beginning to senesce and you think that’s natural then you could carry white
rot along on those bulbs so that’s where it can get insidious at those really
low levels. You want to walk your field every week looking for white rot
but you also want to walk right up to harvest and as you’re pulling those
bulbs for storage you want to look at them too because it can come in right
at the last minute and then go into storage.
On onions you tend to get a little bit of a lag period because when you
plant onions it takes longer for it to develop a root system. White rot has
to have a root system to jump on. I tell people that the best way to control
white rot is to have a bad case of pink root. Pink root tends to limit your
root system, shallower and fewer roots, and white rot’s not a great competitor
so if pink root got there first you’re not going to get much white rot.
This is down at Tuley(?) Lake California the onions were seeded down here in
April and this is like in May, so we’re not getting many roots for white rot
to happen on until late in the season, all of a sudden you get a lot of roots
and then it took off. In different populations you’re getting different
This shows you a summary curve of populations in the soil and amount of losses
and the thing to notice is that all these curves look pretty similar and
they’re all garlic except one, the green bar, but different starting
populations of sclerotia per litre of soil and different yield losses at
harvest, it’s pretty clear that anything above 1 sclerotium per litre of soil
can result in 40% to 100% losses of plants. It’s real common for after a
plant to rot to get 5 or 10 thousand sclerotia on that bulb so if you move
the sclerotia on that one bulb around an area the size of 2 of these benches
you’re going to be losing all those plants the next time you plant garlic.
So that’s why in 2 or 3 cycles you can have the whole field go down by just
moving the sclerotia around and having it build up over 2 or 3 cycles.
It’s very difficult to kill a lot of them and be able to live with this at
low population once you get a high population. That’s why you want to
recognize early and rogue from day one if you can. If it’s already built up to
this level then you have to get these remedial programs we’ll describe, it’ll
help, but it’s only going to bring it down to this level.
This slide shows you how many sclerotia you end up with at the end of the
season compared to what you started with. It’s actually easier to go
backwards here. At the beginning of the season this goes back to those bed
sections that we planted at different populations earlier. In a bed section
where we startd with 500 sclerotia per litre of soil, which is a lot, the
plants died so young that we only got back about 7 or 8 hundred and we actually
didn’t have much of an increase in sclerotia, because the plants were so small
when they died that there wasn’t much biomass for them to reproduce. That
sounds good but that’s still enough to kill all your plants, we had a hundred
per cent loss at those numbers. When we had only 60 sclerotia per litre of
soil we were still losing most of the plants but they were but they were lost
at a bigger stage of growth, more of that loss was from lateral spread, the
bulbs were bigger, and so there was more to grow more sclerotia on and we
end up with 2 or 3 thousand sclerotia per litre of soil. That’s a lot, that’s
a whole lot. When we started at only 9 again the plants were lost at a bigger
stage of growth and ended up with 4 or 5 thousand per litre of soil. Our big
peak here was when we started with 7 or 8 and then they were mostly big bulbs
and just a ton of sclerotia. As you go down here, even though most of the loss
was from plants that were bigger because of lateral spread the populations go
down because ther were just fewer plants that died. But the ending populations
were still quite large, and you notice that the starting populations up here
we couldn’t even measure, we know tht we put some sclerotia in the bed, because
we knew we started out with it because we artificially put it there. Our
assay is only useful at this number so at these two numbers we couldn’t even
find what we had put there. In a bed section as long as this table we only
put in 1 or 2 sclerotia, maybe 1 here and 5 or 6 here, but we’re getting back
enough to kill all the plants in that bed section the next year that we plant.
So roguing will hopefully keep these numbers from happening, and that’s the
reason to rogue, because if you miss roguing that season or so all of a sudden
your fighting really big numbers.
Audience member: How long does it take the sclerotia to form? I mean if
you’re pulling out a plant how soon to you have to pull it out?
You have some flexibility there. If you see the leaf flagging you’re going to
rogue it no matter what’s causing it so if you find it’s white rot that’s bad
news. By the time you see the leaf flagging you usually see a fair amount
growth here, or at least some, because the leaf flagging is from root loss,
and by the time you’re getting root loss it’s usually growing on the bulb and
there’s some sclerotia forming. If you’re waiting until all those leaves
are dead what you have is a big pile of sclerotia here rather than a plant.
So it’s easier to pull them out and get rid of them before those sclerotia
form than it is here. These you’re going to have to dig out with a shovel and
remove all that soil around there also. Now roguing isn’t perfect because
although maybe 99.9% of the sclerotia formed on bulbs there’s a few that formed
on roots, and so that’s one reason why we encourage people to actually dig
soil up also, and even then you’re probably not going to get every single
In Mexico, I think I have a picture of this, where labour is quite a bit
cheaper even in the big commercial fields and so they have a person who’s
skilled at detecting the symptoms of white rot walk the field and they flag
every plant that is dying. They know from experience that white rot’s mostly
the problem. Then a crew comes through and digs out a patch of plants and soil
and bags it up and destroys it. In those fields they’ve been able to replant
every year without increasing the amount of white rot that they experience.
So they aren’t getting rid of it but it hasn’t increased on them and that’s
probably about as good as you’re going to do with a straight roguing program
and without doing anything else. It’s a labour intensive program because
you have to walk there and try and recognize them in the early stages before
it forms just a pile of sclerotia and get them out of there, and also the
digging and destruction take some time. Just a roguing program alone can keep
white rot at bay if it’s not gotten out of hand. Now if they had gone into
a field where there’s a huge patch going down you’re too late, you’re never
going to dig out all that soil. At this stage you can and that’s why if you
haven’t got white rot now learn to identify it so that when it first develops
you can start this program.
Audience member: How long can the mold live as mold?
I didn’t mention that but longer than you or me unfortunately. Well having
said that it’s not actually quite right. That’s another part of my Ph.D
thesis. People had the impression that white rot lived for ever, well the
people that I was working under didn’t believe that it lived forever but that
it had some alternative lifestyle that we didn’t know about and it could
reproduce on something else. Really the answer is neither one. Let’s say
you had a patch here that died and you had 5 million sclerotia there. Well
30 years later you won’t have 5 million that survived, let’s say that you
never planted garlic or onions there again, in 30 years you might have a
hundred that survive, well a hundred is still enough to cause you a lot of
white rot. They do die of but they die of slow enough that after 30 years
you still have some surviving, so the answer is in between. Nobody’s ever
found an alternative lifestyle for this, it could exist, but people have
looked and they’ve never found it to grow on anything else. So it’s a
population game once you get it, if you lose the population game it’s just
not worth your effort to try and rogue out thousands of plants. It is worth
your effort to rogue out a few dozen, or even a few hundred.
Audience member: If you have a small patch in your field I guess it’s an
option that you might be able to flood that one area.
If you weren’t organic you could come in here an spill some fumigant, put
5 gallons of gasoline in that hole and light it, things I can’t formally
recommend but have been done. People have done those kinds of things and
they do work but they’re either against the law, or they’re unethical, but
peole have done them and it’s easy to see why.
People worry about plants carrying white rot,and they do carry white rot,
particularly if you’re working with transplants, like onion transplants,
if the white rot comes in late in the season and infects the stem plate
of the garlic to the point where it doesn’t destroy it enough to cause it
to shatter out and notice it then you can carry a lot in those very late
infected plants and that’s a concern on those and on onion transplants.
Much more commonly it lives with dirt, shoes, we’ll talk about that later,
when we go out to the patch. Commercial fields that I deal with it move
with these boxes, people put dirty garlic into the box, the dirt itself
is in the box and they don’t clean those boxes, it spills out on the next
field. Tillers, all those kinds of things.
I’m going to talk about going beyond roguing. Roguing by itself, if you’re
good at it, and you’re careful, and you collect dirt in addition to the
plants themselves, you can manage white rot just by roguing, but you can do
better than that by using this stimulated germination program that I described
earlier. It’s not necessarily for everybody and every gardener or field
because there are lots of edge effects. If you have a garden or field, let’s
say it’s 10,000 square feet, if you can get a regular rotation program so that
your garlic is in this section in year 1, this section in year 2, year 3, 4, 5,
then you come back here, that takes care of your nematodes, and you’re growing
other things in here in other years. But let’s say you get white rot in here
and you have a patch, you rogued it but you’ve brought in some dirty equipment
or a plant or two but it hasn’t gotten out of hand, so you rogue those out,
but you probably have left a few sclerotia in the field and you’re going to
get some white rot the next time around. You might be able to live with that.
If this is garlic this year the sclerotia that formed are going to be dormant
for at least 2 or 3 or 4 months, maybe half a year and they won’t be
responsive. So you’ve got to come in and trick these sclerotia to germinate.
You can’t do it this year and you probably won’t do it next year, or you
can do it later next year, but where you’re going to rotate to next year you
can treat with stimulant, in fact if it was me I would treat all these areas
as a preventative measure, whether you had white rot or not you might want to
do this in anticipation that you’re going to get white rot some day you can
use it as a preventative program in addition to trying to clean up what you
have. When I say a stimulant you can use onion juice, or garlic juice, and
it’s just as easy to use culls as your main crop. So if you had some garlic
that’s undersize or for some reason that’s not marketable, or get some at the
store that’s cheaper than what your growing. Garlic works better because it’s
stronger, onions, if you use real mild onions you’ve got to use more, but an
effective dilution for garlic is 1 to a thousand parts garlic to water and with
onions you might want to go 2 or 3 or 4 times that, instead of using one bulb
maybe use 5 or 6 bulbs to a thousand parts water. As long as you can smell it
or taste it and it has a little bit of strength to it. We’re doing experiments
now where we’re diluting these things down to the point where we can’t smell
them or taste them anymore. So we’re doing the research now to see how low
you can go. I know that if you can taste or smell it that it’s going to work.
What I don’t know is if it’s more dilute than that whether it will still work.
We’d like to make this suitable for the big commercial guys to use also. In
the home garden or a small field you can afford to err on the high side.
This is probably one instance where more is better, we don’t always do that
with fertilizer, but with this you probably could. So as long as you can smell
or taste it it will turn this fungus on. The idea is to somehow distribute it
over the area that you’re going to crop in the future to the point where you’re
getting this juice stimulant concoction across the area and down into the soil.
So at the end of the day you need to get it as deep as you’ve tilled it. If
you’re tilling 6 inches deep you need to get in 6 inches deep, it you’re
tilling 8 inches or a foot deep then you need to get it that deep. So that
can be more or less heroic depending on your tools at hand. You can water it
on the surface and water it down with water all by itself if you’ve got the
right soil and the right kind of watering system. I’ve done that. It’s
probably a little bit easier to put it on the soil and till it in but then
other crops can get in the way. If you’re just going to water it in then you
can do it at anytime of the year from spring to fall. If you’re going to till
it then you’ve got to do it in those moments when you’re not growing something
else or you’re getting ready to plant something else. The idea is that you
have to get it to tillage depth and you’ve got to do it when the temperature
is between 50 and 70 Fahrenheit. If you’re doing it colder than that it’s
actually OK because the stuff will just stay there and wait until it warms up.
If you’re doing it at the higher end then you’ll probably lose it because the
stuff will volatilize away.
Audience member: So it doesn’t work with the powder?
It’ll work. I didn’t mention garlic powder but you can use garlic powder and
we’ve actually done that in research, we’ve put on about 250 pounds per acre
and that works also, again you’ve got to till it in, you can’t just water it
in. You need 6 months with no alliums before you do it and that includes
volunteers. So you can’t do it on the crop you’re growing now and you can’t
do it if you’re going to leave any behind you can’t do it for another 6 months.
I would wait 6 months anyway because those ones that form on the roots are
going to take 6 months before they’re receptive. So if you’re going to treat
next years field that’s fine. Let’s say you’re here(in the cycle?)
and you want to treat
this field it might not work as well in the year you’re doing this field, but
it’ll work later in the season so you can include that area also. But if you
have any volunteers in here you have to spend the season getting rid of those.
As long as you’re doing this a year in advance of where you’re going to plant
you’re OK. If you get it down to the tillage depth in this temperature zone
and you’re not having an allium issue you will get rid of probably 98% of the
sclerotia that are in those patches. If you have a low level there’s a chance
that you will even eradicate it but you probably won’t. If you had a real
hot spot, let’s say you had an area that was really bad, the size of a car
or bigger, getting rid of 98% is still going to leave you with way too many
to plant in there. So you’re going to want to treat this area 2 to 3 to 4
times before you plant any allium in there. Then you’re down in the area
where you can live with a little it of white rot.
Audience member: I thought you said earlier that the white rot does well in
cool soil and yet you want us to do this when the soil is warm.
Well to me this is cool. It’s a relative term I guess. Let’s say you’re in
the spring and you treated at 30-45 you can actually do that but you can’t
start counting on anything happening until it warms up to this level. Now in
central Oregon some of our soils stay around 50 for a good part of the season.
Some of the Canadian soils are just getting around 50, so were really looking
at June to September for central Oregon, here you might be able to go from
March to October. So you have to consider not just your soil surface but
all the way down to whatever tillage layer you’re working at.
Audience member: Are you just doing a single application or are you doing
a few throughout the season?
The more you do the better you’re going to be so if you’re just watering
on you’re probably not going to get some down at depth and you might want
to do it every time you water. If you’re tilling and you can actually till
down to your tillage depth maybe once a year is good enough. The more you
do the better you’re going to be. I just now that with single applications
that if you do do a good job of distributing the product then every time you
do it you’ll probably knock out let’s say about 95% of the sclerotia. If
you’re compounding that several times you can beat back a high population
eventually and manage a low population where you’ll see very little white rot.
Nobody has the perfect patch, maybe you’ve got a perennial crop here and it’s
got some sclerotia in it, so you’ve got to figure out how you’re going to
factor that in. And you’ve got edge effects. You know you had white rot here
and you’re going to be dragging in dirt from the edge of your garden and you’re
going to introduce sclerotia. Once you get white rot you’re probably never
going to get rid of it totally, but you can manage down to where you’re going
to have a trace of it emerging each year, and then with your roguing program
that’s manageable. Personally I do both roguing and some variation on this and
I would do it even as a preventative on an occasional basis if I didn’t have
Audience member: You said that the powder should be 250 lbs per acre?
That’s what we found effective to get this kind of kill and that was fairly
freshly produced powder, this was commercial stuff coming out of California.
The older powder loses some of the stimulus because they’re all volatile.
If you make up juice a leave it lying around for a week it might not be quite
as potent either. So at the time you use it if you can still smell and taste
it you’re probably still OK.
Audience member: How many litres of that juice would you use?
Good question. I would put on enough so that you know it’s getting down to
the tillage layer. This is conservative, this is more than enough probably,
but if you put on a gallon or two per 1000 square feet you’re OK. It’s
really a very sensitive program. You’re talking about really hormonal levels
in the response of this fungus. And this much garlic powder we’re putting on
less active ingredient to stimulus than we’re putting on methyl bromide when
we use that as a fumigant. Methyl bromide is a very powerful fumigant, a few
parts per million, and so this is down in the parts per million level of
stimulant in the soil. So if you’re smelling the stuff and putting on a
gallon or two per 1000 square feet that’s more than enough if you’re
distributing it well under these restrictions. If you do that I think you’re
going to have some success. Where people have problems is that they come
in and plant too soon. After you make this treatment it take from 1 to 2 1/2
months to get to this point so it’s not really fast, it takes a while. But
it will work so for people who have had failures with treatment and trying
to do it commercially, they come in and plant too soon, maybe they only do it
once and the population’s too high and so you kill off all but 2% but the 2%
that’s still left still hurts them. So they don’t do it frequently enough
and they come in and plant too soon. That’s where we’ve had failures. If
you’re doing it repeatedly for several years before you plant then it works
Audience member: So you don’t need to leave it fallow?
No it’s not going to hurt your other crops. It’s just a question of how you’re
going to get it down if you have the other crops there. You’d have to till it
in either before you plant or after they come out, or you’re watering it in and
you have the right kind of soil that it will actually move. There might be
some other more heroic ways of getting it down.
There are tools that allow you to actually inject liquid fertilizer into the
root system, like there’s a rotating disk that actually pushes liquid
fertilizer in and you could do that with a cover crop.
Audience member: After you gave a workshop a couple of years ago I started
doing an internet search for buying garlic powder to get the price down to
where a person could do it. I found I could purchase a 25 lb. bag. Have
you seen where farmer’s could get together and buy lots of garlic powder?
The companies that I work with a lot, that’s their main product actually.
Fresh market garlic, far fewer acres go into that than into dehydrated garlic.
So they have a lot of it and they have a lot of it that doesn’t make food
grade because it’s off colour or it’s got a high bacterial count or maybe
it’s got a lesser amount of flavour compounds than they want. So they can
make it available cheaper and if you negotiate with them you might be able to
get it, but it’s probably not readily available and you’ve got to go and ask
them. If you just buy food grade stuff that they would market normally you’re
probably going to pay a dollar a pound. To me it’s easier to work with stuff
you grow and make yourself. Get a juicer or whatever and juice it up.
Probably 3 or 4 garlic bulbs will do an area of 10,000 square feet. So not
very much stuff.
After I do this research I’m hoping I can tell the commercial growers in
California that if they were to use as little as a pound of garlic juice
per acre in their irrigation systems and do that a couple of times per year
that they would be able to contro white rot. I can’t tell them that because
we haven’t completed the research. That’s lower than this amount here but it’s
not a whole lot lower. Then the question is whether with simple irrigation
are they getting it down to where they tilled it. They might have to
supplement that with the occasional tillage of powder or spraying on the
juice and tilling that.
The trick is how are you going to make it work for your system and you’re
probably going to be more creative than me in coming up with a way to get
that done. These are the parameters: you’ve got to get it down to whatever
depth you tilled, you’ve got to do it at the right temperature zone, and you’ve
got to wait until the fungus overcomes its inherent dormancy after those
have formed so you’ve got to wait 6 months before you can expect it to
I made it work with test plots and some of the data I’m not going to show you
because we’re running out of time. It’s in those handouts. We started
with populations that were way too high and we did this twice and we were
able to come in and get just a trace of white rot in the subsequent crop
whereas we would have lost everything before those two applications.
But you do have to do it right. You can’t abuse the temperature system
very much and you can’t abuse the dormancy.
If your tillage is shallow, if you’re only ever tilling 3 or 4 inches, it’s
much easier to just irrigate it on probably and it’ll move down that far.
If you pulse it in at the beginning of irrigation and continue to water it’ll
move down that far. The stuff will volatilize back up a little bit.
It has the same volatility as (?) which you’re probably aren’t used to using
but below 50 or so it’s not very volatile so it sits there and it’s not going
to break down and it will still be effective.
Turns out the only things in the world that use the flavour compounds in onions
and garlic are onions and garlic, that’s the only place they’re made in the
world. So micro-organisms don’t break this stuff down particularly fast, it
stays there quite awhile in that form.
Every thing else I have is some variation. It’s more data to explain how we
made this work in test plots. I’ve got some flooding pictures, I’ve got
pictures where we used dehydrated garlic powder. It’s essentially showing
you over and over again. This is the temperature profile for white rot,
temperature and moisture. That’s the other thing, you can’t do this on really
dry soil. If you’re going to irrigate it in you’ve probably got that taken
care of, but if you’re going to use dehydrated garlic powder for example, or if
you’re going to spray it on the surface, the soil has to be at seed bed tilth
with some moisture in there. This shows you that. It’s a little bit old
fashioned, this is in millibars which is out of date, modern terms would be
in Pacals, but nevertheless 300 millibars is like seed bed tilth. So the
germination is optimum right in there and it falls away with respect to
moisture more slowly. Your temperature optimum is right in here around 15 C,
14 -17 C, and so you have your optimum germination at that combination of
moisture and temperature. As you get close to 20C it falls down to nothing,
and below 10C it falls to nothing too. In this case you haven’t actually lost
the stimulant, it will reactivate when the soil warms back up again, but in
this case you actually lose it to the air.
Audience member: Does the moisture need to stay moist for that 1 to 2 month
That’s right you don’t want it to dry out, but if you’re farming another crop
you don’t want it to dry out anyway, you’re going to be keeping it irrigated
or you going to get rainfall. That’s one nice thing about doing it when you
have other crops there, the bad thing is that you might not drive it down as
deep as you like. You can do combinations of things. You can till it in
early then top it up once in awhile with some irrigation. You can just do it
in the spring and the fall. If you’re doing it in the spring and the fall
you’re going to do better than this. You have some flexibility there. I’m
not going to tell you a perfect way to do it because it depends on what your
Audience member: How much organice garlic, what I’m thinking is if you tilled
in the tops of a bunch of garlic, presumably it will grow on that, but when
you’re filtering your water how well do you have to filter it?
It never reproduced on garlic powder, but if your tilling in either ground up
onions or garlic to the point where they’re ground up pretty fine, they’re
going to deteriorate and white rot won’t compete with the things that grow on
them before it does. The stimulants will be there but the white rot won’t
reproduce on it. If you’re putting in a whole onion or a whole garlic clove
and it grows then you’re just going to get white rot again and that’s not
going to do you any good. If you putting in something that’s killed and is
never going to grow then you’re safe. It takes awhile for white rot to
germinate and grow, if you grind up a cull, even if you put in the pulp, white
rot can’t respond fast enough before something else jumps on it and it’s a
very poor competitor with other things except after it’s infected it.
We actually have worked on a commercial product that is a petroleum derivation
of one of the stimulants, diallyl sulfide. It was registered in New Zealand
and used there very successfully for a couple of years. It just got
registered here in 2003 but the company decided to stop manufacturing it, the
reason was they figured there wasn’t a big enough market and it just wasn’t
worth it, it didn’t fit their program. It probably wouldn’t have been
acceptable organically because it’s petroleum, but it’s essentially
equivalent to part of garlic juice. We’re looking for a different
manufacturer now to see if we can reactivate that but right now there isn’t
one. Just wanted to tell you that it did get to the point of commercialization
though. We’ve applied it with shank injectors, with tillers, it works fine.
In the US, I forgot in Canada, but in the US a lot of these natural products
were deregulated from the EPA which said they don’t want to have anything to
do with them, it’s OK to apply things like garlic juice or garlic powder as
pesticide. I don’t know what the Canadian rule is but if I were you I wouldn’t
feel bad about putting in cull juice that you make yourself. Whether that
fits your concept of either organic rules or the Canadian pesticide rules I
Audience member: I don’t think it fits the pesticide rules. In your home
garden you can put on what you like but commercially I think you have to use
a registered pesticide.
I don’t know, you’re going to have to work through that. I wouldn’t feel bad
about it because it’s strictly an organic material. You could say you’re
disposing of it rather than treating soil I suppose. You get into gray areas
I do want to show you one last slide. It’s a review, particularly I’ve shown
you botrytis, nematodes, white rot and fusarium. Those are the ones we most
commonly confuse with white rot when we’re walking fields. Fusarium will
always attack right at the base plate and move up with that watery beige mold,
but you don’t actually see a mold you just see the watery rot. Botrytis most
commonly infects at the neck and it can move all the way down here but it
doesn’t get on the roots so they tend to be hard to pull up, but it can form
a few sclerotia, it’ll move inward and the plants will be stunted. Usually in
cool wet weather. The bulb nematode these leaves will be bloated typically
and a little later in the season, separate from the stem plate. With white
rot I’ve ground that into the ground, they won’t have any roots and they
pull up easy, you’ll at least see some plants with white mold on them and you
ought to be able to find sclerotia with a hand lens, some people with good
eyes can see them without. You might have to look at a lot of dirt. Some
of these over here, they can be embedded in the leaf sheathes, they can be
very superficial after that leaf sheathe has rotted away. It depends on
which stage you get them. If you pull it up and see nothing but white fluff
then you might have caught it before the sclerotia have actually formed and so
that could confuse you a little bit too. Usually if you have set of plants
you can find one where the sclerotia have formed, if it’s just one, and you
just have white mycelium, look for sclerotia because usually by the time you
see white mycelium you can find at least some sclerotia.
Audience member: I have a question about excessive dying leaves because the
older leave, some of them die from old age.
Yes, you get towards maturity and you’re going to get senesence. So we’re
looking at premature senesence. If it’s dying too early, you’ve got one that’s
beginning to die and the rest of them aren’t that’s what your worried about.
As you get closer to harvest it gets more difficult so really late season
white rot can be tricky. Usually botrytis has run it’s course by then.
Botrytis doesn’t like it warm and sunny so by the time you’re getting to
maturity you’re probably not seeing any more botrytis, but you can see white
rot, and so in our certification system in Oregon, California and Nevada the
ones we think
slip through our system are the ones where this happened really late and by
the time the stuff was naturally senescing we couldn’t really tell the
difference. But if your pulling them up, and I think a lot of you are pulling
them up when they are slightly green and hanging them, you can look at them
then. If you’re seeing something that clearly has some white mold on it and
is partly rotten then you want to be suspicious about it. In our case we
tend to leave those in the ground and dig them up a month later after they’ve
totally dried down so we miss it.
Audience member: Down in Mexico where they’re growing the fields and they put
the flags on them, they just do it visually?
Well this is several growers and they raise their own seed and they have some
fields that they designate as seed and they have their commercial fields.
All their seed fields are in this program and they usually have a designated
field hand of some kind or the farmer walks about once a week. Their seasons
are a little different than ours, they cull from first thing in the spring
until harvest. They’ll walk them once a week and they’ll flag plants and that
guy will come through or another crew will come through and rogue all those
Audience member: Do they care whether it’s botrytis or?
Yes they do. They don’t have much botrytis down there, they might have a
little fusarium, but they just treat it the same. So they’re just being
conservative. Usually if it’s a new field somebody who really knows white
rot will go in and make the diagnosis, because if the field has had it
before they know they have to get rid of every plant and all around it and
everything that goes down, and they maybe catch up a few fusarium with
their white rot.
Audience member: What temperature…(?)…
It’s a time dosage thing in the old hot water treatment program for nematodes,
I actually did that study, they would heat the bulbs to 120 F for half an
hour. If the white rot was loose in the water they would die. If you had
some white rot that was behind some scales or in a brick of sclerotia that
rotted down from the previous season where you had 2 or 3 hundred sclerotia
in a little brick some of those would survive.
Audience member: Is it possible to treat on a small scale …(?)…with hot
water or boiling water, would that make any difference…
I guess I’m not clear what you’re treating. Well if you’re pulling the
plant are you talking about killing what’s on the plant or killing what’s
left in the soil?
Audience member: In the soil.
The soil is so heavily buffered that pouring a pot of boiling water in the
soil would probably kill some of them but it wouldn’t penetrate very far into
the soil. If a root is 10 inches long and you had 3 or 4 sclerotia growing
on a root you might kill a few of them but you’re not going to kill all of
them. I don’t think that would work very well. You could build a fire over
the hole, bank it and let it burn for several hours. People have done all
sorts of thing like that. I had a grower in Nevada near a mining company and
they use a lot of sulphuric acid, after they had extracted gold and stuff,
and he would pour like a cup of sulphuric acid in every hole where he had
taken out white rot. The soil would boil and you could actually hear it.
I guess it worked but I’m not sure it’s ethical.
Audience member: How long has white rot been around?
It was first given a name back in England in the early 18 hundreds. It was
first found in the US in 1917. I know the California situation better
because I monitored it down there. It started in the Bay area of
California around San Francisco around 1930 and it followed the production
of vegetables down through the south bay area and then down into the
Gilroy(?) area in the 40’s and 50’s and it drove out most of the garlic in
the Gilroy area and down in the Monterrey county area in the 60’s and
eventually drove garlic over to the San Juaquin valley in the 70’s and 80’s
and then they probably have about 10 more years there before they use it up.
They’re going to start moving garlic up to the Sacramento valley and they’re
running out of seed areas too. Central Oregon’s going under and Nevada’s
Audience member: So it isn’t a problem in the east at all?
It’s a problem in the east where they’ve overwintered onions like around
New Jersey. A lot of onions are grown in the spring through fall and it’s
too warm for white rot in most of those areas. So if they grow over winter
onions in New Jersey and parts of New York and then it’s a problem in
Canada even in spring planted garlic just because it’s cool up around Ontario
and Guelph, Bedford marsh area(?). Someone asked me how many people in the
world work on white rot, there aren’t too many. The only people in North
America besides me are Mary Ruth Macdonald at University of Guelph, she
works on the Bedford marsh, and some day you might like to have her come and
talk to you, she might have a little different perspective. There’s a couple
of people in New Zealand and Australia. There used to be quite a few in
Europe but they’ve kind of given up on it. A few in Spain. Not too many
people work on it, I’m one of the few left.
Audience member: When you say they’ve given up on it do you mean they’ve given
up growing onions.
There’s not a lot of research funds available for it. Probably some of the
more interesting things being done today are some breeding programs being
done in New Zealand and Wisconsin, the USDA program in Wisconsin. I don’t
know how the …(?)… for breeding against white rot. There’s no recognized
germ plasm that’s persistent on onions, and you can’t breed garlic anyway,
but there’s some possibilities. Probably the more innovative stuff on
bio controls is being done in New Zealand and Australia. Nothings come out
of there that I would feel would be of benefit here but they do have products
that give us partial control, but partial control isn’t good enough for most
people. In a bad situation that’s the difference between 100% loss and 75%
loss. In an organic situation maybe they would work better than that so some
of those products might be things to try in some of your settings.
There’s work to be done on fungicides but that’s not really relevant for this
group and none of them are really super anyway. They control white rot at low
levels but they don’t control it when you’ve got a lot of white rot. Seems
like it overwhelms them. It’s one of the tougher diseases to control in the
world, there’s certainly others but this is one of them. We’re just lucky
that it doesn’t go onto anything else. If it had you would probably have a
thousand people working on it and have more solutions, but with it being
such a relatively minor crop and very hard to make progress on people tend not
to work on it. And the industry doesn’t throw a lot of money at it.
Audience member: Is it a big issue in Asia?
It’s hard to say. We can’t get any information out of China. My guess is
that it probably exists there but you have people who are willing to rogue
out any bad plant and they probably manage it like I’m talking about here, but
we can’t get any data out of China and we’ve tried for decades to find out
whether they have a problem or not. It is a problem in Russia. It would be
surprising if China hadn’t had it at least, but whether it’s ever blown up on
them I don’t know. If they start becoming more corporate type farms I wouldn’t
be surprised if it got out of hand. Some parts of the world it’s just too
Audience member: I’d like to hear you talk a little bit about how we’re
going to go wandering through a patch of white rot and not all carry it home.
Well I’ve got some disposale booties so those work pretty well as long as
you’re not puncturing them so if it’s really stoney or there’s brambles but
they work pretty well in most situations. So I’m okay with that, hopefully
you are too. I’ve never had white rot in my garden yet so that’s probably a
decent indicator that I’ve been careful. The thing about white rot is that
it’s real easy to forget even if you’re not growing garlic you’re moving
seedlings around to plant so if there’s dirt on it you could be moving white
rot aroung with that, or dirt on potatoes, or a tiller, or a shovel, so it’s
when you’re not thinking about it that you’re at biggest risk. So if you’re
sharing seed and equipment those are always risky ventures. The more
careful you are the better off you’ll be.
Audience member: How risky do you suppose it is to buy plants from nurseries?
It’s hard to put a number on it. In the Walla Walla area of Washington where
they grow the Walla Walla sweet onion that’s popular white rot has been a
nasty problem there for many years since the 40’s. At least a few growers
have been willing to send out transplants that they’ve grown on white rot
infested soil. Which is disturbing. I know that northern Europe was infested
the same way out of Holland until Holland cleaned up their act. Nearly all
the onions planted in Scandinavia were transplants, either as sets or
transplants coming out of Holland.
Audience member: I was thinking of horticultural plants or cabbages and
Well it depends on what they grow them in. If they were grown in white rot
infested soil they might not even know about it. So there’s always a risk,
it’s just a matter of how big of a risk, all life is a risk, so the less you
know about the situation the bigger the risk is.
Audience member: Can you look at the soil with a hand lens and tell if it’s
It’s impossible to tell even if it’s mildly infested. That one per litre
we can barely measure that, if it’s above that we can find it, but that’s
enough to blow you out of the water. At the low levels we can’t find it
at all. It’s really hard. A soil analysis isn’t good enough. The best
thing you could do if you were buying some seed from somebody is to go look
at their crop the year that they’re growing it and do your own survey and
talk to them about any history they’ve had.
Audience member: How damaging is it to leeks?
Probably a little less damaging but they are susceptible. I can point to
literature where people have done research because it’s a problem but
having said that it seems to be less of a problem and probably a combination
of the fact that they have a little more limited root system and they seem
to leak out fewer of those volatiles and turn on fewer sclerotia. They do
get it, and all alliums, as far as I know, can get it. Most of the work
that’s being done in the world is on onions because they’re a far bigger crop
than garlic. Some people have the impression that onions are less susceptible
but they’re not. They’re less susceptible if you’re growing them in a hot area
or a hot time of year where they’re susceptible over winter but not in the
summer. So people in some areas think that onions don’t get it but I tell the
people in the Columbia basin who are primarily growing spring planted onions,
fall harvested, they want to grow some over wintering onions for export market
soon as they do they’re going to start seeing white rot. We know white rot
has occurred in some of those fields and in home gardens nearby so it’s just
a matter that you’re going to start finding them if you start planting that
Audience member: In the previous workshop you gave …(?)
Yes that was in a slide that I skipped. The thing I tell those people
Columbia basin that the best thing they can do is to keep planting spring
onions and harvesting in the fall because they’re probably forcing a lot of
sclerotia in those fields to grow and then they don’t make it up to the bulb
because it’s too hot. So the best thing they can do is to keep planting the
crop they’ve been planting because it avoids the issue and probably regularly
sniffs out sclerotia that leak into those fields from the Walla Walla area or
Central Oregon or somewhere. But I’m assuming nobody in this room is from a
real hot area like that so it’s not a tool you can use here. But it is
something you can use instead of applying a stimulus just grow a crop in the
hot time of the year.
Transcribers note: This was the end of the class room presentation
although more interesting discussions took place in the garlic patch
we examined. One thing I remember of particular interest was that
the success of solarization would depend on how deep the sclerotia were
which in turn depends on how deeply the soil was tilled. This brought
up the idea that no-till farming might be best.
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