cc >> Tom Zinnen: Welcome, everyone, to Wednesday Nite at the Lab.
I'm Tom Zinnen. I work here at the UW-Madison Biotechnology Center and also for UW Extension Cooperative
Extension, and on behalf of those two groups and our others partners, the Wisconsin Alumni Association, the UW Madison
Science Alliance and Wisconsin Public Television, thanks again for coming to Wednesday Nite at the Lab.
We do this every Wednesday night, 50 times a year. Tonight I'm delighted to be able to introduce to you
Brian Hudelson. He is affectionately known as Dr. Death, we're not sure affectionately by whom, because
of his love of plant diseases. Brian received his BS in botany, bacteriology and molecular biology, his master's in
biometry and his PhD in plant pathology, all here from UW Madison. In 1998, he became the director
of the Plant Disease Diagnostics Clinic. The Plant Disease Diagnostic Clinic is part of the college of
Agricultural and Life Sciences here at UW Madison and is also part of Cooperative Extension, UW Extension.
The clinic, and Brian in particular, provides expertise in diagnosing plant disease problems, provides information
on diseases and their control to a wide range of clientele throughout the state of Wisconsin.
That's everybody from farmers, to gardeners, to homemakers, and homeowners, and anybody in between.
He'll tell you how you can send in your plant disease samples. It is a fee for service. >> We'll talk about that too.
"Service for fee," as we call it. But I think it's a wonderful combination.
It, along with the entomology clinic, Entomology Insect Diagnostic Clinic and the Soil and Plant Analysis Clinic are
three, I think there might be a fourth one. >> Turf Diagnostic Lab. >> Turf Diagnostic Lab, that I'd
like everybody to be aware of because they're pretty wonderful services to keep your plants growing.
I, too, am a plant pathologist, so it's a particular joy for me to be able to ask you to join me in welcoming Brian to Wednesday
Nite at the Lab. [APPLAUSE] >> Brian Hudelson: Thanks very much, Tom.
I think our mic is on. If you can't hear me in the back, please let me know. Actually, you're pretty lucky,
this is my first talk this week so my voice is actually doing well. I'm finding that as I get older
that my voice tends to kind of fade out on me when I give a lot of talks during the week, but we're good for today.
I am Brian Hudelson. I do run what's called the Plant Disease Diagnostics Clinic, and what I'd like to do tonight is
kind of give you a brief overview of the sort of things that I do in my job, quite frankly.
And we will talk about some specific diseases but I kind of want to talk a little bit about who we are, what we do and why
we exist. So with that, we're going to try to save questions towards the end because I guess that makes
it a little easier for filming tonight and streaming. So if you have any questions, jot them down, and we'll get to
them at the end of the presentation. So what is the Plant Disease Diagnostics Clinic?
The acronym PDDC is much easier to write on a package when people are sending me samples than Plant Disease Diagnostics
Clinic. We actually are part of UW Extension and primarily what we are is basically a support
laboratory to support the County Extension offices here in the state. We have 72 counties.
Each of those counties has an Extension office, and those folks are varying levels of expertise with working with
plants. And back in the mid-1970s there was a decision that was made that really there needed to be
some expertise to help folks in the county offices diagnose or identify plant diseases and provide information on disease
control. And the first diagnostician was Sister Mary Francis Heimann, and she retired in 1998 and I took
over from her. And at that time, when Mary Francis started in the clinic, there was this partnership that
was put together between UW Extension and the University of Wisconsin Madison, particularly the College of Agricultural and
Life Sciences, to establish this clinic in our Department of Plant Pathology. So that's where I'm housed.
That's where my home is. So I'm what's called integrated staff. I'm technically a UW Extension
employee, but my home is in one of the academic departments here on campus, particularly plant pathology.
And we've had this relationship for, what, about 35 years now. So it's been a long and very extended relationship between
Extension and the College of Ag and Life Sciences. In addition to those particular partners, more recently, within
about the last 10 years, my lab, as well as Phil Pellitteri's Insect Diagnostic Lab, has become part of a national
network of diagnostic clinics. This was a network that was created through a piece of legislation post-9/11.
It was actually called the Ag Bioterrorism Act of 2002, and it provided the framework and some funding for basically linking
together all of the land-grant university diagnostic facilities that dealt with plant and insect issues in the country into a
large network, and the whole idea behind doing this was to make that network more powerful in terms of monitoring for new
and exotic diseases and insect pests that might enter into the country. And we've been part of that for
the last 10 years. It will be interesting to see whether that continues. The funding for that is
basically on the chopping block at the federal level, so we don't know whether we'll be funded with that but we're still
a partner with that. It's been a great relationship in working with other diagnosticians around the
country. We work with all of these groups. We have a lot of other partners
as well. I see one of my colleagues came in the back. He told me he was coming
tonight. This is Bob Dahl from the Department of Ag, Trade and Consumer Protection.
They have a lot of folks who work with plants, dealing with insect pests and diseases as well.
We collaborate pretty closely with them. I have a counterpart at the state in the Department of Ag,
Annette Phibbs, who I work with quite closely in diagnosing certain types of problems. I also work quite closely with
the folks at APHIS, the Animal, Plant, Health Inspection Service, which is part of the USDA.
And, in fact, we were at a meeting this morning where we kind of gave summaries of what we had seen over the summer in
our various jobs and clinics. So there are a lot of folks working together. I have a team in my department
that I work with. There are four other Extension faculty in plant pathology that I work with quite closely, Patty
McManus who is our fruit pathologist, Paul Esker who is our field crop pathologist, Amanda Gevens who is our
vegetable pathologist, and then Jim Kerns who is our turf pathologist. And I saw Jim as I was going out
to the parking lot today, and he's said he's talked to this group in the past. And I had an opportunity to work
very closely with Jim, actually, this past summer. We'll talk a little bit about that later in the talk.
So, again, my lab is a support lab. We provide support for the county extension offices, but
quite frankly what we do is expanded beyond that, and we now not only take samples from county offices but we also take
samples from a variety of other sources as well, including consultants and homeowners, quite frankly anyone who's
willing to send me a sample I'll look at. I'm not picky. And I must say that I do, I am a
true plant pathologist. I get very, very excited about diseases. And I will act very, very goofy
during particular parts of this talk because I think what I do is really cool. Now, a lot of the people that
I'm interacting with who are having these problems with their plants don't necessarily think that the diseases are really
that exciting. But what I try to do is give them a sense of why I think I'm excited about these things, and
I do think plant diseases are pretty cool, but my bottom line is basically to help provide them with some information on
how to manage whatever type of disease problem that they have. So what does the PDDC do? We look at a lot of plants that
are very sick and ugly looking, quite frankly. And you're going to kind of understand why I tend to be
somewhat tongue in cheek sometimes about what I do. When you're looking at rotting, disgusting plant materials, 8,
10, 12 hours a day for an entire year or more, I've been in this job for 13 years, you can either get really silly about it on
occasion or you can get really depressed and I'd rather be pretty silly about it. So what do we do?
We look at plants. We look at all kinds of different plants. A lot of the plants that come
into my clinic are field crops. So things that farmers are growing like soybeans and corn, alfalfa, small grains.
Those are some of the type of plants that I see from an agronomic standpoint. I also see a lot of vegetable
samples, and I work quite closely with Amanda Gevens, again, who is our vegetable pathologist, particularly on a
disease called late blight. I'll talk a little bit more about that specifically towards the end of my talk.
We deal with fruit crops of all kinds. This summer I had the opportunity, actually last
summer but more so this summer, to start working more with cranberries, which is a major crop here in the state.
Patty went on a sabbatical and so I was working quite closely with one of her grad students doing diagnosis on the cranberry
crops. But we deal with basically any type of fruit crop. This was the year, quite
frankly, of raspberries. We had more raspberries come into our clinic than any other year that I can ever remember.
Not my favorite crop to work with for many reasons. One, they hurt when you work with them.
I don't like plants that hurt me when I work with them, but that's the case with raspberries.
And they also tend to be relatively difficult to diagnose the problems. There are a lot of diseases that
they can get and trying to differentiate what disease is causing the problem can be a little bit of a challenge.
We deal a lot with evergreens. And quite frankly my three top problems this year in the clinic were on spruce trees.
And we'll talk about pretty much all three of those a little bit later on. But we do see a lot of conifers
coming in. Make a lot of money off the conifers, quite frankly. We also deal with deciduous
trees and shrubs like apples with those really bright yellow spots. One of the cooler, prettier
diseases that I get to work with, a disease called cedar apple rust. We'll see more of that, again,
later in the talk. We deal with herbaceous plants, both outdoors, things like hostas and phlox and those sorts
of plants. We also deal with indoor plants. Although, quite frankly, that's a very small proportion of the
plants that we deal with. We also have a very thriving specialty crop industry in the state.
I have a lot of experience working with ginseng. In my previous job here on campus I was basically the
program manager for the Ginseng Research Program. So we do a lot of ginseng, and so I'm still kind of considered
the expert in that particular area on campus. And then more recently we've started doing a lot of soil
assays. There are certain pathogens that you can actually extract from soil, and we do a lot of tests
for nematodes, which are small parasitic worms that can be quite detrimental to particularly a lot of our field
crops, soybeans in particular. We do some tests for soil-born fungi or fungi-like pathogens that can cause problems in
alfalfa and also in peas. We'll talk about that. So we do a wide range of testing on a wide range of crops.
About the only thing you probably don't see up there, what don't you see up there? Turf.
We don't do turf. And that's because we have a special lab that deals with turf diagnostics.
It's run by Paul Koch who is a staff member in the Department of Plant Pathology under the direction of Jim Kerns who is
our turf pathologist. What else does the PDDC do? When I'm not looking at plant samples, I'm doing lots and lots
and lots and lots and lots of outreach. I do about 70 talks a year. And sometimes it's a field day,
sometimes it's a talk like this. I do a lot of teleconferences. Somebody who came in said they'd heard me on the radio.
I do the Larry Meiller show, Garden Talk, every once in a while. I also used to do about every
month a radio show in Milwaukee that's no longer on the air, but we did that for eight years, a group of us in UW Extension.
And that was a lot of fun. I do television programs with Shelley Ryan. She's a hoot to work with.
She's really lots of fun. We have a lot of fun. Last time we did a shoot we were doing something on Dutch Elm
Disease and ended up shooting in the rain which was quite an experience. So that's always enjoyable
working with her. The other thing that I do quite a bit of is writing. We try to do a lot of
informational sorts of publications for our clientele. In particular, when I first started with UW Extension there
was a big call amongst the horticulture agents in UW Extension for very condensed, very, what do I want to say?
Easy to use fact sheets for homeowners. And so as a team we came up with these publications called the
University of Wisconsin Garden Facts. And we have about 200 tittles in that series now that cover
diseases, insects, general horticulture and a variety of different topics. And I've been involved in that
in terms of writing a fair number of those and also I serve as the editor for that particular series.
So that's something that keeps me busy in the wintertime. So it's really about figuring out diseases and trying to
provide that information to the general public in whatever manner really works. Who does the PDDC serve?
Again, pretty much anyone. We have, what, about five and a half million people in the state.
Personally, I consider every one of those people one of my clients. So if you live in the state of
Wisconsin, you can send me a sample. We do charge for our service, but I do have a policy, and I'm
very careful to make everyone aware of this, that if there is someone who cannot afford a diagnosis who really needs it,
we'll do the sample for free. And actually we've done a lot of free sampling recently with late blight, again a disease we'll
talk about a little bit later. We had a problem with that on tomatoes particularly in 2009 and 2010.
We decided to offer testing for that particular disease free of charge. So it was a disease that had
huge impact for the potato industry in the state and also our fresh market tomato industry and we decided that we needed to
do that free of charge. We also do free diagnostics on diseases that we call regulatory diseases.
And I'll describe some of those a little bit later as well. Kind of the commodity or the groups that we serve, again, in
the center here the county extension agents really are technically my primary clientele, but we also will
serve what I call primary producers. So anyone who is actually growing the plant that's having
a problem. So that can include farmers who are growing things like, again, corn and soybeans.
It can include people in the horticultural industries like greenhouse growers who are growing crops like geraniums or
other types of bedding plants. It could be someone in a nursery growing trees or shrubs. Those are all primary producers.
Also included in that group in the upper right-hand corner, a lovely picture of some nicely diseased phlox, homeowners.
Homeowners are a big group that bring in a lot of samples to my clinic. Because I'm located, my clinic
is located in Madison, we have a lot of folks in the Madison area who are avid gardeners who are very interested in knowing what
diseases are. They tend to be able to pay for the service so they're willing to bring in a sample, and so we
get a lot of walk-in clientele. And we do have a walk-in service through our clinic. The other group that we help out
as well are what I call consultants. In particular, I have a lot of interaction with the arborists
in the state, the Wisconsin Arborists Association. And I've routinely visited with them at their meetings.
I give talks for them, but they provide a lot of samples for my clinic. We do a lot of trees and shrubs.
In fact, until recently about 80% of my sample that is came into the clinic were ornamental samples, either trees, shrubs or
herbaceous ornamentals. So we do a lot of samples that are really not productions crops, per se, but just plants
that make people's lives better by making the environment more beautiful. But we do have other folks in
that kind of consultant area. A lot of crop consultants as well. And I do some training for that
group as well. I do some sessions called IPM Scout School. Three different locations in the
state where we basically train crop consultants on how to identify diseases of field and forage crops.
How do we do it? How does the PDDC do what it does? Well, here is what I would like
to say is what happens in my clinic. A symptomatic plant comes in. I have an epiphany and there's
the diagnosis. And we have a fact sheet we pull off our wall and then we're done and I put out my hand and say
please pay me my $20 for this sample. That's not exactly what happens. As you can kind of tell if I
take my hat off, there's not much hair up here anymore and that's because typically the process looks more like this.
[LAUGHTER] Kind of a ran/walk sort of process where we're going all over the map trying to figure
out where things are. We certainly do get some of the samples where it's, I look at it, I know what it is, we're
done. I call them the easy money samples. And they're nice when they come
in. But, quite frankly, we don't see a lot of those anymore. Saw a lot more of those when I
first started in the clinic 13 years ago, and I'm hoping that part of the reason why I don't see those anymore in the clinic,
much as I love them, is because we've done a good job educating the public on what these easy to identify diseases look like and
what needs to be done with them. And I think we do spend a lot of time trying to train the general public, to train master
gardeners and also to train our county extension agents so that they can recognize these diseases so that they don't have
to send them in to the clinic for a formal diagnosis. On the other hand, what has happened is the samples that I
get nowadays are a lot harder to do than when I started. They're more complex, they take a lot more time, and in a sense
they're more challenging for me, and I have to say that when I've been working with a really tough sample we finally figure out
what it is, it's very, very satisfying. And it's really nice to have those sorts of challenges in a
job after 13 years. So I am grateful that I see a variety of things and do see new things all the time because it
really keeps me on my toes and it makes the job very, very interesting. I really do love my job.
I think I have one of the coolest jobs on campus, quite frankly. So I do enjoy doing all this
sort of thing. What else? How else can we talk about what I do?
Well, I would not be a plant pathologist if I did not put a slide of the disease triangle in my talk.
And this is kind of the basis on which we talk about diseases when try to teach our students about what a plant disease is
and how to manage that disease. And what the plant disease triangle does, or the disease triangle, it basically
summarizes the three important components to a plant disease. You need to have a susceptible host that's a plant that can
come down with a particular disease. You need to have a pathogen which is some sort of
microorganism that can cause the disease. And we'll talk a little bit about what those are in just a
second. And then another very important component of a disease is a favorable environment that
allows the plant, the susceptible plant and the pathogen to interact. And this is a process that
occurs over time. What we see as a manifestation of that interaction is disease. And usually what we're really
seeing is what we call symptoms. So some abnormality in the plant that gives us a clue that something's going on that isn't
quite right. And part of my job when I'm diagnosing is not only to identify what the disease is but
try to figure out the various components in the triangle so that I can provide management information.
How to control the disease. And really when you're trying to control the disease, what you're trying to do is trying to
eliminate or at least reduce the importance of one or more of the corners on this triangle. You're trying to modify the
environment in some way so the disease is less likely to develop, you're trying to make a recommendation to grow something
else other than the susceptible host that's having the problem or you're trying to figure out ways to get rid of the pathogen
or at least reduce the amount of the pathogen in the vicinity of the susceptible plant so that you don't see as many
infections. And so that's kind of the basis of this sort of information that we're providing.
Now I don't, in my reports to my clients I don't put it in the context of the disease triangle. We just kind of tell them what
they need to do. Grow a different plant. We'll tell you which ones we think are appropriate.
Thin your garden to modify the environment. That will help. Or, at this time of the year,
one of my big recommendations is get out there and do good fall clean up because all of those disease causing organisms are
surviving, or at least many of them, in that old plant debris. Those leaves that have fallen off your tree are the remains of
that plant that has died back over the summer. So again, that's part of what we look at when we're trying to
figure out what's going on. One of the things we do is collect a lot of information. We have to kind of collect
information on all three of the corners of the disease triangle. The bane of my existence, I have to say, from the susceptible
host point of view are a lot of the new varieties, epitomized by this lovely arborvitae in the left photograph on this slide,
that have been bred over time for yellow foliage. I can't tell you how much I hate yellow foliage varieties because
they arrive at my clinic oftentimes just saying this is an arborvitae, and my first thought is boy is that diseased.
[LAUGHTER] And then I have to step back and say, wait a minute, call up the person who submitted it
and say, do you happen to know which variety this is? And then they tell you it's something like Golden Glow
Arborvitae, or some such. That's probably not a real variety name, but once you get a sense that it's been bred for
that then it makes your life a lot easier. But it really points out the fact that you really have to
know what a healthy plant looks like of that particular variety of plant in order to really assess whether it's diseased or
not. But it really does make it a challenge with some of the newer varieties that have been bred.
And quite frankly, I go out shopping and I have to say, my friends hate me when I go shopping because every plant
buying experience is a chance to see diseased plants quite frankly. And I've seen hosta varieties
that are being sold as varieties that are swear are infected with viruses. And they just have the symptoms
of a viral infected plant they've been released as a true variety. And you have to keep in mind
that certain types of plants we actually want them infected with particular disease causing organisms.
Anybody like poinsettias? You like poinsettias? You know what a native poinsettia looks like out in the
wild? It's a tree. It's a tree. And actually those plants are
infected with a type of pathogen called a phytoplasma. It gets in the phloem of the plants and causes the plants to
stunt and bush, and that's why we get our lovely, really bushy, lovely looking poinsettias. And actually, Shelley Ryan and I
did a lovely little segment on when bad pathogens went good and how pathogens can actually help in our lives.
But, again, knowing what a healthy plant looks like or what a "normal" plant looks like is very, very important.
Other sorts of information that we collect, we spend a lot of time asking about patterns of disease.
Particularly, if you're dealing with some sort of field crop, I want to know how the disease is distributed in the plant.
Is it uniform? I told them I would genuflect quite a bit. Is it uniform in the field?
Is it patchy? Are there really sharp delimitation between diseased and healthy tissue?
And in kind of this middle top photo you can see an alfalfa field where there's a very distinct line down the middle of
the field, and that sort of very sharp junction between diseased and healthy tissue really gives you a sense that there's
probably some human component in what's going on here. And it's these sorts of patterns that we look for.
And in that particular case what the grower had done is they planted a companion crop with the alfalfa, they planted oats,
and the half on the right they harvested very early, they basically cut it back as kind of a green manure, and on the left
they let it grow to a fair size. And that basically modified the environment and made it much wetter on the left side of the
field, and that was very favorable for disease to develop. Other things that we look for,
the bottom two slides with the arrow, we look for temporal patterns, how the disease changes over time, because
sometimes we have things other than disease that are going on. There are certain types of physical damages, insect damage,
those sorts of things that aren't true diseases that can happen in a field, and oftentimes that sort of damage
tends to arrive fairly quickly but it never progresses. It never gets worse. It kind of stays the same.
With diseases they usually get worse over time, particularly if we have a lot of wet weather. Water is a real driving factor
in a lot of diseases. And you can kind of tell that from the slide in the upper right.
Sorts of environmental conditions that we're trying to get information on. Certainly temperature but lots
of time we want to know about rainfall, drought, flooding, a lot of information about water because a lot of the organisms
that I'm dealing with very much require substantial amounts of water in order to infect. We'll talk more about that a
little bit later. But all of these sorts of types of information are important. We also get information on soil
type, topography, fertility, just a wide range of information because the more information that we have the better we can
do at giving a good specific diagnosis on why a particular plant is having a particular problem.
What else do we do? Well, once we get samples in the clinic we initially kind of triage them.
And that usually involves doing some sort of macroscopic sort of examination. We're going to look at the plant
by eye to see whether we can get a brief or write a brief description of what we're seeing that's going wrong.
And what we look for are different types of symptoms that usually fall into five different categories.
This lovely squash in the upper left has a lovely rot symptom. That's one of the major groups. It's called necrosis so
basically a degradation of tissue. And there are all kinds of different types of rots.
All kinds of different plant parts can rot. Fruits can rot. Roots can rot.
Crowns can rot. Pretty much anything on a plant will rot under the right conditions.
We look at kind of whether they're dry rots, which tend to be more typically fungal in nature, versus wet rots.
If it's really slimy and disgusting, it's probably a bacterial rot. Although that's not always the
case. Sometimes fungi come in and initially cause the problem, and then there are other non-disease
causing bacteria that will follow and basically finish off the job. But they wouldn't cause any
problem on their own. It's just because something else came in first. But we have to kind of tease
that sort of information out of the sample and sometimes we can tell a lot just by looking at the sample visually.
We also look for discolorations. An example in the upper center photograph. A rose with these lovely yellow
line patterns. And sometimes it's not this distinct. Sometimes it's just a general
yellowing, sometimes a general purpling. General yellowing is oftentimes an indication of a nitrogen
problem in the plant. Purpling can be a phosphorus deficiency. Line patterns like you see in
this rose oftentimes are an indication of a viral infection. So knowing what different types of pathogens will cause
different types of symptoms you can really, again, get a lot of clues about what might be going on just looking at symptoms by
eye. We also look for what are called overgrowth symptoms. So galls, swellings, big kind of
cancerous growths on plants. And this is my favorite of the overgrowth symptoms. I call this affectionately poop
on a stick because that's what it looks like. It's a disease called black knot.
It's specific to cherries and plums, anything in the genus Prunus, quite frankly. And it looks like an animal has
defecated on the branch. It's very distinctive. It is one of my easy money diseases by the way because I
can look at the symptoms on that and I know exactly what is it and what to tell a client to do which is basically prune.
And sometimes I recommend what we call basal pruning which is one single prune at the ground level.
[LAUGHTER] We can come back to that. I can tell you probably my most embarrassing story in the clinic
about an elderly woman and a tree that was a memorial to her dead husband and me sticking my foot in my mouth.
We'll come to that maybe a little bit later. Other things that we look for: undergrowth symptoms.
So where plants or plant parts are smaller than normal. You can see this, this is actually a soybean field in the
lower center here. It actually has a lovely combination of symptoms, if you want to talk about several
things that you could look for. One of the things that you can see right away is there's a lot of yellowing in those plants in
the center, and it's kind of in a nice big round patch. That's important to notice that, that it's not uniform, it's
actually concentrated. There's yellowing and then the other thing you notice is where those plants are yellow you can
actually see between the plants you can see the soil between the plants where the greener plants in the foreground the canopy is
entirely closed. So there's a lot of stunting going on in those yellow plants that are smaller than normal.
So we've got stunting. We've got a patch and we've got yellowing. The yellowing is probably
due a nitrogen deficiency. These are soybeans which should nodulate, so they should be producing nitrogen on their own
and that probably means that there's something going on in the root system that's interfering with water and
nutrient uptake and nodulation of the plant, in this particular case a nematode pathogen called soybean cyst nematode.
And I'll show you that one in a bit as well. The other major group of symptoms are the wilt symptoms
where the plants just get droopy. They can't get enough water. And there are a variety of
different types of disease causing organisms that can cause that sort of symptom. Now at my house when I see
wilted plants like this it is not a disease problem. It is a drought stress problem because I use what's called the
wilt test for watering my house plants. If the plants are wilted, they must need water.
Now, that's not a great way to treat your plants, but I run little experiments on my house plants at home to see how long
they will survive without water. Some for several months, quite frankly. Unfortunately, for most people
when they see a plant like that, what's your reaction? You water it, right? And if it doesn't recover what
do you do? You water it again. And usually the problem at that point is a root rot of some
kind. And you know what you've done? Remember that favorable environment corner of the
disease triangle? You've made that really big. You've made the root rot pathogens really, really happy
by providing all that water. So, again, looking at those symptoms, getting a sense of whether the soil is dry versus
wet, again, gives you a sense about what might be going on. So, again, types of symptoms: necrotic symptoms, discoloration
symptoms, overgrowth symptoms, undergrowth symptoms and wilting. Those are the five major groups.
You're basically getting our introductory plant pathology course tonight in one hour. It usually runs 18 weeks.
The other thing we look for are what are called macroscopic signs. We talked about symptoms.
That's an odd looking plant, some way in which the plant looks weird. When we're talking about signs,
what we're looking for are actually pathogen structures or the pathogens themselves. We're actually seeing the
organisms that are causing the disease. And, quite frankly, a lot of times what we're looking for, in
the middle top you see a lot of white on that African violet flower, that's actually a fungus growing on the surface of the
flower. It's a powdery mildew fungus. You're primarily seeing fungal threads or hyphae, I'll show you
a microscope slide of that in just a second, and a lot of spores. And these are the reproductive
structures of this particular fungus. And we do spend a lot of time looking for spores because
that's a major thing that we need to see in order to identify most fungal pathogens. On the upper right and also on
the upper left there are a group of pathogens called the rust pathogens which oftentimes produce very, very distinctive
and very visible spore masses on plants. Usually what you'll see if you're looking in a home garden,
it will look very similar to what you're seeing in the upper right where you have these very bright orange spots that you can
actually if you rub against them you'll rub off an orange powder. And those, again, are spores of this rust fungus.
Very, very cool organisms. I've always said that if I went back to graduate school and decided to do plant pathology
over again, I'd either probably study rusts or powdery mildews because I think they're really, really cool fungi.
And we see a lot of them in the environment. Other sorts of things that we look for, if you take a look at
the soybean seed in the lower left, you see all these little black things that look like mouse droppings or rat
droppings, those are actually fungal structures. They're called sclerotia and it's a resting structure of a
fungus that causes a serious problem in soybeans. The disease is called white mold, and these little
structures sit around on the ground. They can stick around for on the order of five to seven years in
the soil, and they germinate in the spring. And in the middle slide you can see these little tiny things
that look like little mini mushrooms, and that's what are produced out of these black mouse dropping-like structures,
and those are what produce the spores for this particular fungus. Another famous disease that also
produces these sclerotia is something called ergot. You've probably heard of the Salem witch trials.
Have you ever heard of St. Anthony's fire? You may have heard of that. Both of those are, there's
thought to be a connection between ergot and both of those. Ergot is a fungal disease that occurs on small grains.
Rye is a very susceptible host. Back in the middle ages, rye was the primary grain crop that was used to produce bread in Europe.
And oftentimes it was infected with this fungus, and those sclerotia, those little resting structures produce all kinds of
crazy chemical compounds. Many of them closely related to LSD. And they would get harvested
with the grain, ground up in flour and back baked in bread. And these compounds would not break down in the heat of baking
and people would eat this and basically have all kinds of hallucinations. They would have problems with
circulation. It basically really fouls up pretty much most of your body and at high enough concentration
will kill you. And it's thought that the Salem witch trials were also associated with ergotism, so
eating ergot, and they think that some of the women that were accusing other people of being witches were probably
hallucinating because they will get a hold of some of these compounds in bread. So very interesting disease.
There's a lot of interest in this particular disease nowadays actually in medicine. You can take some of these
particular products, distill them and at the right concentration they can be used medically.
In particular, they can be used to induce labor during pregnancy. What else do we look for?
Well, once I've looked at the plants at kind of a macroscopic level, next thing is to start looking at the tissue under a
microscope. And I spend a lot of time at the microscope. We finally got some really nice
ergonomic chairs, so I don't have back problems anymore. That's very important as I get older.
And the sorts of things that we look for, in the upper right hand corner I talked about this term hyphae or fungal threads,
we really spend a lot of time looking at what fungi look like. This is how they grow during their non-reproductive stages.
And depending upon the particular fungus that I'm looking at I can identify it based on what the hyphae look
like. There are very few fungi where I can do that but there are certain ones that I can.
The one on the upper left here is a fungus called rhizoctonia, nasty little root rot pathogen, but it forms T-shaped cells
where it branches. And that's very diagnostic for that particular fungus. We also look for reproductive
structures, lower left. In this particular case, one of the reason I love powdery mildews is because of their
sexual reproductive structures that are produced around this time of the year. They're incredibly ornate.
That photograph is at least 400 times normal size. And look at all the ornamentation, those little arms
that are coming out. They look like antlers. We have a new powdery mildew that showed up in the state
about five years ago. It's a European variety. It occurs on maples. Those little, they're called
appendages, those little arms, they come out and they look like tuning forks that do little curly Qs on the end.
So this beautiful, beautiful structure producing lots and lots of spores that can cause lots and lots of disease
problems. The other thing that we look for sometimes are nematodes, lower right.
And these are worm-like organisms that we find in soil, and I actually spend lots of time at the microscope actually
counting these. I have what's basically a white blood cell counter that I have sitting next to me and I'm just
clicking away. I think I drive my technician, Ann Joy, crazy because click, click, click and when I get a
hundred there's a ding. So she's very patient with me when I do that. Upper left we also look for
bacteria. Not a great way to identify exactly which disease you're looking at but certainly gives
us a sense of whether there may be a bacterial pathogen present. What we do is oftentimes we see decayed tissue on leaves.
It has kind of a watery sort of look to it. That's the macroscopic symptom that we look for.
Then we'll take a little bit of tissue at the edge of that between the diseased and healthy tissue, put it on a microscope
slide in a drop of water, slice across it with a razor blade and then we look at that cut surface.
And if there are bacteria there, you can see all the granule material in the upper right in that slide, those are all
bacterial cells just oozing out. It looks like the Nile Delta, quite frankly, coming out of the plant tissue.
And once we see that then we'll go on and do other techniques to try to get a better sense of which bacterium we're dealing
with. And that kind of comes down to the next thing that we do with our samples which is basically
we do a series of techniques where we either incubate tissue under high moisture or we can also do certain types of
isolation techniques where we're trying to coax the disease causing organism to grow out of the tissue so that we can
identify it on particular types of growth media that we have. When we're talking about incubations, we use either what
we call moist chambers, we oftentimes do these are petri plates lined with a little bit of filter paper that's wet,
stick a leaf on that wet surface and let it sit for two our three days and if there is some sort of fungal pathogen there, it
will produce spores in that time and then we can look at those spores under the microscope to identify what we're seeing.
We also do what are called humid chambers. Sometimes we leaf tissue that's very, very delicate.
Potato leaves are particularly problematic. If we put it in contact with wet filter paper, it will just
disintegrate. So what we do is we put wet filter paper on the bottom of plastic bags, some dry petri
plates on top and then kind of lay the tissue over the top, and we just create a nice humid environment and we can look for
different types of pathogens in that more delicate tissue without as many problems with the tissue just kind of
disintegrating over the three-day period. We do isolate bacteria, that's shown in the upper right.
We have a couple of workhorse media that we use. One's called YDC. It's a yeast dextrose calcium
carbonate medium which is shown here. It is a very white color. There's a particular bacterial
pathogen called Xanthomonas, and if that particular organism is present we get these lovely very mucoid, so kind of slimy, yellow
colonies. They're very easy to identify. We also have some fungal media that we use.
One is potato dextrose agar, so it's got basically boiled potatoes that have been strained, a little bit of sugar
dextrose and then some agar to solidify it. And we use that as our workhorse for most fungal pathogens.
And this particular organisms, that lovely buff color, that you're seeing, that's the pathogen.
We'll talk a little bit more about that disease in just a few minutes. So, that's one step that we do.
We can also do soil assays, as I mentioned before. We do a fair amount of that. The ones that we really
concentrate on, we do a lot of soybean cyst nematode testing, and that involves taking a soil sample from a soybean field and
we actually sieve it through a very fine sieve and then we place some of the material in a very thick syrupy sugar
solution, sucrose. So right off we actually buy sugar at the grocery store for this.
And you basically put it in a centrifuge, and these what are called cysts will actually float out on the top of this material.
And these cysts, what they basically are female nematodes that have filled with eggs.
So this particular nematode, when the female lays eggs she lays them internally, her body swells up like a bag, originally
she's white in color but then she dies and the bag, this cyst turns brown. And we actually find these in
soil. And then what I have to do is crush those open to release any of the eggs or juvenile
nematodes that are inside and I get to count those. And the one that I did, I didn't actually count 5,000 but
eventually when we did the math calculation back it was about 5,000 nematodes per hundred CCs of soil.
And we've had as many as close to 30,000 in some fields, and that's a huge number that can really significantly impact
soybean production. You can get probably a 50 or more percent yield reduction in a situation like that.
We also do what are called bait techniques. This is a very general test it's designed to look for certain
types of root rot pathogens. Take a soil sample and you float or you pour over that soil a one to one mixture of sterilized
distilled water and, interestingly, filtered sterilized Lake Mendota water. I swear what's the protocol
says. That's how it was developed. So if you ever see me laying on one of the docks with my arm
down in the lake, I'm not getting a tan, I am there collecting water for this particular assay.
And then what you do is you take little bits of citrus leaf, and we actually keep a plant at one of our greenhouses so we can go
and harvest leaves, cut little squares out of the leaves, float it on the surface of this water and after a certain period of
time we can come back and look for structures that are characteristic of these root rot pathogens that is have started
to grow in the citrus leaf pieces. The other big money makers for the clinic, soybean cyst
nematode actually we make a fair amount of money. We've probably made $6,000 or $7,000 on doing those samples.
That's $22 a sample. We actually do that particular testing in cooperation with Shawn Conley in our Department
of Agronomy. He gets a grant from the Wisconsin Soybean Marketing Board to actually, we're
actually able to do up to a thousand nematode samples a year at $22 a sample. The other, our most expensive
test that we do is the one in the upper right which is a soil assay. It's $150 and it's very labor
intensive. We actually get a soil sample from an alfalfa field, we plant five different varieties of
alfalfa in that soil that have resistance to different types of pathogens and then we basically do a stand count, we flood the
soil, we watch the plants die and then we basically, every plant, and we do about 90 plants per one of those little plastic
squares, every plant we rate or evaluate the root system for disease. I can't remember if that one is
a one to five or zero to four, but in any event there's a scale that we use for healthy to dead, and then we do a statistical
analysis to basically see whether there are statistical differences between the different varieties, and based
on those differences we can make a recommendation of what sort of resistant variety a grower should use.
The other test that we do, again, that we make a fair amount of money, I inherited this test from a colleague,
Bob Rand and his former major professor, Don Hagedorn, developed this test, and they tested for years, and I've
inherited that. It's a pea root rot test. And actually this is an exciting test because I actually can get
information from the canning companies on how valuable this test is to them. What they do is they want to
contract with growers to grow peas in a particular field, but they don't want to grow in a field where there's a high
likelihood of pea root rot. So they'll bring us a sample, we pot it up, we plant peas in it, we let the peas germinate, and
once they are about seven days old then we start flooding the soil with water. It makes the conditions very,
very moist, and then we allow the plants to grow for an additional three weeks, and after a month we harvest all the
plants and we evaluate again the root systems. And it's one of the most gratifying tests that I do
because you can actually see the differences as the plants are growing in the greenhouse. We have positive controls which
are soil where we know there are lots of root rot pathogens. Those plants are dead as a door nail.
We have a negative control where we do it in a sterilized potting mix. The plants are usually huge and
very healthy looking. And then if you look at the test soils they vary everywhere in between.
And we kind of divide the different types of soils into three different groups, either good, bad, or uncertain.
And the economic data that we've gotten from the canning company is that if we can identify a bad field and they instead of
planting in this bad field planted it in one of good fields, they can actually double the gross profit per acre.
So it actually can save them hundreds of thousands of dollars every year. So it's a very gratifying test
for a variety of reasons. But we do spend a lot of time doing these sorts of tests. Pea root rot is a winter
activity. I usually do that in December and January, and it's lovely in Wisconsin to be inside a
greenhouse in the middle of the winter where it's warm and sunny and really lovely around green and growing plants until, of
course, I kill them off. We also use a lot of serological techniques. There's a company in Elkhart,
Indiana, called Agdia Inc, and they have basically specialized in the diagnostic field in developing serological
techniques, particularly for testing for viruses, but they also test for a variety of other types of pathogens as well.
And they've come up with what are basically the equivalent of a home pregnancy test for pathogens.
It's a dip stick test. You take a little bit of tissue. You put it in a plastic bag that has some rough material inside
that will help grind up, and then you have this little dip stick that you put in the solution, it's a combination of
the plant sap and some buffer that's kind of a water/mineral solution. That's in the bag and the
material is sucked up by capillary action that's in the test strip. And if you get one little pink
line, it's a negative result. If you get two pink lines, it's positive. These are very specific tests so
usually you're testing for a single virus or a single pathogen. They are very, very useful and
they're fairly inexpensive. In fact, I oftentimes recommend those sorts of tests for greenhouse growers who
oftentimes have a lot of virus problems. So for about $5 a test you can get a good sense of whether
you've got a virus problem. We do more kind of conventional serological techniques, like ELISA.
That's shown in the far right. And we can do that to test for a large number of samples all at once.
Oftentimes we don't do a lot of that. We tend to go with the test strips if we can.
Traditionally, it tends to be a little more expensive than our clientele is willing to pay for. There are certain tests where we
can use this. There's a potato disease called bacterial ring rot, is of regulatory concern here in the
state and it's one of those diseases that if you are a seed potato producer, you never want to see this particular disease
in your field because you will be banned from growing seed potatoes for, how long is it Bob?
Is it 10 years? >> I don't recall. >> Five to 10. That's a long, long time.
So it's a very destructive pathogen that you don't want to see if you're a seed potato producer.
And we occasionally have to use conventional ELISA to test for that. We also use some DNA-based
techniques, particularly polymerase chain reaction, or PCR. This is a technique where you
can look for particular stretches of genetic material of a pathogen that are specific for that pathogen.
You basically make lots and lots of copies of that very specific piece of DNA and then you can visualize it using a dye.
And we do some of that. Again, it's usually too expensive for us to really do on a routine basis for most
clientele, but we do offer certain tests in that arena. And more recently we've actually gotten into DNA sequencing.
We had a new pathogen for Wisconsin show up in the state this past summer on wheat. It's a fungus called
Cephalosporium, and we actually sequenced that particular organism to verify that it was actually the pathogen that we
thought it was. So we do do all these sorts of techniques. And then what really we need to
do once we've kind of decided which tests we're going to do, we've got our macroscopic observations, microscopic
observations, we've got all the other information that we've collected, we need to kind of put it all together and come to
a conclusion about what's going on. And as an example, one of the very common diseases that I see,
we'll get complaints from a client that they have an Austrian pine that looks really, really unhealthy.
A lot of brown branches, brown needles, just looks horrible. If you ever want to see a tree of this type, you can come over
to my lab. I'll take you right outside. We have Austrian pine that has this particular disease.
I'm hoping that grounds doesn't cut it down because it's a great teaching tool but they may eventually.
But if we see this sort of kind of symptom at the landscape level then what I start looking at are the individual branch
tips, and if I see a lot of uneven lengths in the needles with some sap production in that branch tip, then I start pulling
those needles out and I look for these little structures on the far right. One of my colleagues calls these
the Hershey's Kisses of death. [LAUGHTER] And that's Denise Smith, who works with our forest
pathologist Glen Stanosz. I love that. But they do look like little brown Hershey's Kisses that pop
up through the base of the needles, and I pluck those off, put them on a microscope slide, squish them to death and out
will pop those lovely little large brown spores. And I love spores that are big. I love spores that are colored.
What I hate are getting little tiny colorless elongated spores because there are tons of fungi that produce those.
It's very difficult to identify. But when you have something big and obvious like this we know that it's a fungus called
Diplodia, and particularly if we started to see these symptoms during a period where there's a lot of drought, that's another
clue that we're dealing with this Diplodia. This is a disease that tends to be more prevalent on drought
stressed trees. And definitely seeing the fungus in the tissue is kind of a dead give away.
But all this information is very, very important as I am, again, still putting it together and reporting back to my client.
And pretty much every client gets a customized letter/report. I spend a lot of time writing letters.
Sometimes late into the night at home. And sometimes it's to the point where if I never have to write
another letter again I would be very, very happy, but it's one of the things I've really, really emphasized when I started
in the clinic. I figure if people are paying me to do a diagnosis, they need something in their hand that
shows that I've done my job. And what we do is we try to provide as much information as possible on the disease and how
to control it. What I found very early on was that I didn't like writing two- or three-page letters to
describe all of the things people needed to do, and that was part of the impetus for developing these University of
Wisconsin Garden Facts because then my letters become very short. Here's what we did, here's what
we saw, this is the disease, here's a lovely fact sheet for you to read about it, if you have questions, contact me.
So that's what we do in the clinic. And we do a lot of it. This year has actually been a
very interesting year because our sample numbers are way, way down. I think we're really seeing the
effect of the economy. People don't want to spend $20 or $25 to have a diagnosis. We're probably going to be down
about 30% over last year. Normally we've averaged, over the 10 years or 13 years that I've been in the clinic, about
1700-1800 samples per year. And this year we'll probably end up, my estimate is around 1100 or 1200, somewhere in that area.
But it doesn't seem like it's been less busy in the clinic. We've gotten a lot more requests via email.
People like to send me digital photos, which I love to see if they're in conjunction with a real plant sample.
I can't do a lot of diagnosis specifically off of photos, unfortunately. Primarily because a lot of what
I'm looking for is microscopic. So certain things like black knot, that poop on a stick, that one I can do from a photo, but
if it's a lot of other diseases, I really can't tell much from just a photograph. But I love to see those
photographs, particularly landscape shots, because oftentimes if I can see how a plant is situated in the
landscape that gives me that ancillary information so I can write a very specific report and provide very specific control
information to a client once I do know what the disease is. Or if I find out that it doesn't look like a disease, that
happens a lot, if people don't provide me with that ancillary information, they get a two-page letter from me.
I call it my litany letter which basically I try to list everything I can think that might possibly gone wrong, it's
usually trees, might have gone wrong with that tree that may have caused, usually it's branch dieback, unfortunately.
Their branches die, they send me the branches, it's not a branch problem. If I've got landscape shots,
sometimes I can see things like girdling roots or trees that are poorly planted, and then I can comment specifically on that in
the report. But we do try to be at specific as we possibly can. Our policy for charging is you
send in a sample the first time, we may request a follow-up sample. If we've charged you $25 the
first time around, we won't charge you anymore for a follow-up. If you send in a sample that was
a $20 charge to begin with, the follow-up would have cost you the extra $5, we'll charge you the $5 the second time around
but you pretty much max out at $25 per sample. So what sort of diseases that I see?
And hopefully this will answer some of the questions for the people that said they had some disease problems in their yards.
We see a lot of common diseases, and a lot of these fall into the category I call the easy money diseases.
These are ones that I can pretty much look at and tell you what they are. We talked a little bit about
powdery mildews. We see that on all kinds of different plants. This particular photograph is a
powdery mildew on zinnia which is probably one of the problematic hosts amongst the annuals.
Phlox and bee balm are another great host for this where it can cause a lot of damage. On woody ornamentals it's
primarily a cosmetic disease, but if you grow ninebark, particularly diabolo ninebark, we can get powdery mildew that's
so severe that it will cause branch tip dieback. And that's very unusual for powdery mildew.
Another fun disease to diagnose because it's so easy and actually quite pretty is something called golden canker.
The official name is Cryptodiaporthe canker, named after the fungus that causes the disease.
Plant pathologists can be very cruel. They do like to use Latin names as part of the common names, and
I prefer golden canker. It's more descriptive. It's specific to pagoda dogwood. Usually occurs on trees that are
planted in the wrong location. People love pagoda, those are the ones are the really kind of horizontal branches.
Lovely trees but because they're so pretty they want them right in the middle of their yard where everybody can see them.
So they're usually surrounded by grass and in direct sun. These are understory trees that like cool temperatures, and they
like a lot of moisture. And if you've got turf growing up around them that tends to stress them for water, and when
the trees become stressed this golden canker disease comes in. How many people like roses? People like roses?
Yeah, I hate roses. I'm sorry. I really am. It's another plant that hurts me
when I work with it so that's the reason I don't like them. But I know people, if they like roses, they're usually really
rabid about liking roses. And the bane of probably every rose grower's existence is black spot.
These roughly circular black spots, kind of fringy edges, will eventually cause defoliation, particularly older
varieties that have not been bred for resistance. But a lot of the newer varieties have gone through an extensive
breeding program to breed for very high levels of resistance to this disease. So newer varieties tend to be
very good. We don't see a lot of disease but the older more traditional varieties will see a lot of
problems with this, particularly if it's a fungal disease. Fun disease I talked about before, cedar apple rust.
This is a disease that actually is a rust that has two different hosts. There are rusts that spend their
entire life cycle on a single plant. This particular one actually bounces back and forth between
two hosts. This is what you typically see in mid-May to mid-June. If you ever see these, I think,
beautiful, slimy orange marmalady masses, sometimes they look like orange little octopuses on your red cedars or
other types of junipers. That's this particular disease. And the spores that are being produced in that orange mass,
they're not reinfecting the junipers or the red cedar, they're actually infecting an alternative host which include
things like apples, crab apples, quince and hawthorn. If you're on campus and want to see the alternate phase for
this, go over to Slichter Hall where the Allen Centennial Garden is. If you're a gardener, you should
know where that is. Right across Babcock Drive there's beautiful hawthorns that are just loaded with the
alternate phase of cedar apple rust. One of the best stories I've ever heard, it made me laugh
harder than I think I've laughed in a long, long time, Karen Lawrence who is the former head of grounds here on campus,
said that a student came up to her one time, mid-May, the student's comment was, I love this time of year,
because that's when the red cedars bloom. [LAUGHTER] And what she was seeing was
cedar apple rust galls. [LAUGHTER] So we talked about poop on a stick and the control
for that. Pruning, oftentimes basal pruning. And actually the white that
you're seeing on there, that's actually another type of fungus that's parasitizing the pathogen.
So it's not the organism that's causing the disease, it's a secondary organism. And then the number one disease
that I saw this year on any crop was the one on the lower right. That's Rhizosphaera needle cast. If you went around anywhere in
the state, you probably saw a lot of spruces that were losing a lot of needles. And particularly if it was
interior needle loss, so near the trunk out, it was probably this disease. Very, very common and quite
frankly it probably wasn't anything that happened this year so much as our wet springs in 2009 and 2010 that really
contributed to us seeing a lot of this disease in 2011. Those wet conditions really set up the trees to have a large
number of infections, and with a little bit of heat stress and water stress that we had this year we really saw a lot of
needle loss from this disease. So these are diseases that I like to see in the clinic because they're easy for me to
do, particularly after I've had a challenging hard sample it's nice to have something like this to come back to where I feel
really good that I've made a quick diagnosis. Sometimes we have diseases that get a lot of press that we will
diagnose in the clinic. Usually pretty much every year somewhere in the state we're going to have some press on oak
wilt. It's a very, very important disease. We have a lot of oaks in this
state. This particular disease is kind of a representative disease for a group of diseases called the
vascular wilts. And those include oak wilts, Dutch elm disease, which I'm sure nobody's ever heard of, and
also another disease called verticillium wilt, which is kind of one of my favorites. But oak wilt causes a lot of
damage to oaks. The pathogen actually enters into the tree through wounds. At least when it's initially
introduced to an area it's brought in by sap beetles that have spores of the fungus on their bodies, and they come in
to feed on the sap in a wound, drop off the fungus, the fungus infects the water conducting tissue and leads to blockage of
that tissue, and that leads to the wilting of that tree and it can be quite rapid. Particularly in oaks in what's
called the red oak group, those are the oaks with the pointed lobes, those particular trees can die within one growing
season from this particular disease. And Dutch elm disease and verticillium wilt both function
very, very similarly. Verticillium wilt is a little different because that fungus is a soil born pathogen and then
enters through the roots. But the wilting sort of symptoms that you see are very typical, and it's all due to blockage in
the xylem in the water conducting tissue. More recently the big disease in the news here in the state was
late blight. And that really started in 2009. Now, late blight has been around forever.
Any of you Irish ancestry in the audience? I certainly am. We are probably sitting in this
room because of late blight. That's what caused the Irish potato famine in the 1840s and '50s and led to lots of folks
moving out of Ireland. Caused a lot of deaths through starvation as well. We've had late blight in the
state in the past. It was just prior to 2009. We hadn't seen late blight for about seven years.
And when it came in it was very, very interesting. There is this pathogen that causes late blight but there are
lots of variants of the pathogen. And some of the variants, like potatoes, a little bit better
but they will infect tomatoes. The variant that came in 2009 preferred tomatoes. We saw our first cases in
potatoes and it took a long, long time for us to see the disease on potatoes. Interesting, the first case on
potatoes in 2009 was in one of our Extension entomologist's test plots at Arlington. He was very chagrinned.
And particularly because his wife was a late blight expert through USDA as well. That didn't help as well.
[LAUGHTER] The number two case on tomatoes, I have to acknowledge this as well, the number two case in
the state, actually on any crop, was in my dad's home garden. I was accused by certain folks of inoculating my dad's
tomatoes, but that was not the case. [LAUGHTER] It was really funny.
He called me, they were going to a flea market or something and they wanted me to let their dogs out, and they said by the way
our tomatoes are wilting, could you please take a look at them. And I walked about four feet away from them and I knew it was
late blight. This is a very destructive disease. And it basically kills plants
and the reason why it is so important is because we have a huge potato industry here in the state.
And if the pathogen comes in and gets into home gardens, there's a local source of the fungus, actually it's not a fungus
anymore, it's a water mold, but spores can be produced that can eventually end up in our potato producing areas in Wisconsin.
So large impact. We did a lot of testing for this, did a lot of testing for free.
In 2009, we did about a hundred samples for free. Virtually all of them were positive for late blight.
We offered the same sort of service in 2010, and virtually none of them were late blight. Most of them or more common
disease of tomatoes called septoria leaf spot. It's one of the diseases that causes the tomatoes to defoliate
from the bottom up. Very, very common. So we continue to monitor for that for free.
Other diseases that we've seen, I really know that I've arrived as a plant pathologist or that plant pathology has arrived as a
science when I hear a segment on NPR about plant disease. And there was actually an NPR piece, I believe it was last
year, on basil downy mildew. And we actually had our first reported case in Wisconsin last year as well.
And I think the number two case was actually in my neighbor's backyard. I went to film a segment on
vegetable diseases with Shelley Ryan again and I was looking for other things and all the sudden I looked at their basil and sure
enough it had downy mildew. It causes real yellowing in the foliage, and if you flip the leaves over and look on the back
surface you're going to kind of grayish-purple, fuzzy material which is actually the pathogen sporulating on the undersurface
of the leaf. And then more recently and every once in a while I'll get a call from a newspaper, particularly
in the eastern part of the state. Although, there's a lot of this disease in Dane County
apparently this year. These leaves with these huge black blobs, splotches on the leaves, very round oftentimes,
and if you look very carefully at the center of those round spots they look like somebody left a fingerprint in the
center. And this is a disease called tar spot. Again, fairly cosmetic disease
but we see if usually closer to the lake. And I think it was the Milwaukee Journal Sentinel that called me
and was asking for comments on that disease this year. So diseases do make the news. Sometimes they're very important
economically, sometimes they're more cosmetic issues, but we do get some press every once in a while.
And then my favorite diseases, as Bob will attest, are the regulatory diseases. Ramorum blight is one that has a
long history. It's a disease that for a while was pretty much isolated to California, particularly
northern California and southern Oregon. A lot of oak trees were dying in the area.
The original name of this disease was sudden oak death. And, unfortunately, one of the nurseries out in that area sent
out a whole bunch of plant material from a site that they eventually discovered was contaminated with the pathogen.
And so there was a lot of work, when was that? About five years ago where tons and tons of, trace forward, so
they had to follow all these plants from California to where they will been shipped and to try and track down where these
plants had gone. And we still monitor for this particular disease. We've never found a confirmed
case in Wisconsin, but we still, it's a disease that has regulatory impact. Huge potential impact on a wide
range of woody ornamental and also some herbaceous species as well. Plum pox is a disease, it's a
viral disease, that was found out east. We, again, we've never had a confirmed case here in Wisconsin
but we continue to watch for it. It can be very, very problematic on Prunus species, so plums, cherries, apricots, peaches.
Again, we don't produce a lot of those fruit crops here in Wisconsin, or at least not large amounts, so it's not as
important here as farther south. Thousand cankers disease is another one we haven't seen here but it's kind of the current
disease of regulatory importance that we're watching. It's been more of a problem in the southwest US on walnuts, and
it's called thousand cankers because it's associated, actually the pathogen is fungal pathogen.
It's brought in by insects that tunnel under the bark, and every where they tunnel an infection occurs, so you get lots and lots
of these insects visiting an individual tree starting lots and lots of individual infections, thus thousands.
It really does look like there's thousands of infections in the trunk. And you can see all of these
brown areas on the wood. And those are all conglomerations of individual infected areas in the tree.
And it will kill walnuts. And we are very concerned about that. There's kind of a quarantine or
you have to be very careful transporting wood out of areas that have confirmed cases of the disease.
And so, again, the Department of Ag is very concerned about that. I've been doing a fair amount of education in that particular
area. Probably the regulatory disease that I'm most proud of from my standpoint is Ralstonia wilt.
Myself and one of my student hourlies as well as Caitilyn Allen who is our current department chair, she's a world
expert on this particular disease, and the group of us were able to publish a first report of this particular
pathogen or a variant of the pathogen on geraniums. There was a variant, we got these geraniums that came in
that were sick. They had this wilt disease. We got this, it's called Ralstonia solanacearum out of
the plants, and I had an undergrad at the time who wanted to do a senior thesis and so I said, well, there are all these
variants, these little specialized groups within this particular species of bacterium, go and find out which variant
this is. We were expecting one variant and it came back as a different variant that had implication of
potato production because it was slightly more tolerant of cold weather. And Lynn got a paper out of that
which was very fortunate for her. She did a great job on the project.
It was a nice feather in the clinic's cap for having picked up on this. What's interesting about this is
that was pre-9/11. After 9/11 the federal government developed the list of select agents, and this
particular bacterium, this variant that goes to potatoes ended up on the select agent list.
And we had an introduction post-9/11 where the FBI and Homeland Security got involved because we had to determine,
well, DATCP and APHIS had to determine whether it was an accidental or an intentional introduction.
And as it typically the case these are accidental introductions. But interesting pre-9/11 versus
post-9/11 how this disease was actually looked upon. And to kind of finish up, sometimes in the clinic we deal
with non-diseases. In fact, this summer was really the summer of, in many ways, non-diseases.
Sometimes what we deal with are nutrient sort of deficiencies. The most common one that we deal with is a problem in oaks called
chlorosis. We have a lot of limestone bedrock here in Wisconsin, and it tends to really cause the
soil PH to be very, very high. And when we have high soil PHs what that basically means is iron gets locked up in the soil
so the trees can't take it up, and you get very, very yellow oak leaves with very distinct green veins.
And, again, it's not really a disease. There's no microorganism involved.
It's really a fertility or a soil PH issue. Similarly, if you ever grow tomatoes you probably had
blossom end rot where the bottom of the fruit rots away. Again, it looks like a disease but it's not.
There's no real microorganism that causes that disease. It's a nutrient deficiency. It's basically a lack of calcium
in the fruits. The big non-disease that we dealt with this year is in the center.
There was a new herbicide put on the market called Imprelis. Did a great job on controlling things like violets and other
broad leaf weeds in lawns. Unfortunately, the manufacturer didn't realize, even though they'd done a fair amount of
testing, that under certain conditions it could be a great herbicide for spruce and pine as well.
And so there are hundreds if not thousands of trees that have been severely compromised or even killed through use of this
herbicide. And we spent a fair amount of time basically looking at samples that had these weird
distorted growing points. The tips of the branches were very elongated, very twisted. The needles were very tan and
really disgusting looking from uptake of this particular herbicide. And then sometimes we see what I
consider really cool organisms that aren't causing any problems. I just think they look really
cool. The one on the top is what we affectionately call dog vomit slime mold because it looks like
somebody's dog has up-chucked in your mulch. These are very common when you have spread new mulch.
And they are very, very transient. They usually only last about a week but they're very colorful
and they look very disgusting. And if you really want a hoot, do an Internet search on Texas and slime molds.
Back in the mid-'70s they had a lot of this pop up, and they thought it was an alien invasion.
[LAUGHTER] It does look kind of weird. And then we get the rather embarrassing fungi, the
stink horns that look like a particular piece of anatomy. I get phone calls about those. It's a very kind of embarrassing
discussion. These are fungi. They're basically mushroom-like structures, but they look very,
very weird. I vacation down at Disney World routinely and I was very, very excited two years ago
because I saw three different types of stink horns at the resort where I was vacationing. So I was in plant pathologist
heaven. So we do see a lot of different things that are really, really cool.
Like I said, I love my job and I hope I've conveyed some of that tonight. I'm going to stick around for a
while if you have specific questions that you'd like to ask. But if you think of anything
after we're done here tonight, feel free to contact me. This is my contact information. You're welcome to give me a
call. Also, it's usually pretty easy to get a hold of me via email. Just be patient, sometimes it's
really crazy in the clinic and it takes me a few days to get back to phone calls and email messages.
Also you can visit my website and also the UW Extension horticulture website for a lot of additional information on
plant diseases and other cool stuff. Thanks, Tom. [APPLAUSE]