Wisconsin Gardener:
Celebrate Fall #1504
Original air date: November 1, 2007

Plant viruses

Shelley Ryan:
I'm at the UW Madison Arbotetum with UW Extension Plant Pathologist Brian Huddleson, and Brian as you know, you're affectionaly called by many of us in the industry. Dr. Death.

Brian Huddleson:
That's right, that's my nickname.

Shelley:
It's cute. But that's because you focus on the downside of gardening you know the diseases that can kill our plants.

Brian:
That's right.

Shelley:
So what unhappy news are you bringing us today?

Brian:
Well today we're going to talk about-- a little bit about plant viruses amongst the sort of disease causing organisms that I have to deal with these are actually typically less destructive in many ways than a lot of the things that I deal with. Because they usually don't kill plants but they oftentimes make them aesthetically unpalatable so that you really don't want them in your yard.

Shelley:
So no panic, but at the same time something that we should worry about.

Brian:
That's right.

Shelley:
What have we got here?

Brian:
Well this is a Petunia plant that has a virus called Tobacco Mosaic Virus, and this particular virus is very widespread. It has a very wide host range that goes to not only petunia but tomatoes and as the name implies, tobacco. And that can be a real source of the virus if you're a smoker or use tobacco products you can actually pick up this virus on your hands, from smoking.

Shelley:
From smoking, another reason to quit.

Brian:
That's right, and if you handle your plants you can actually innoculate your plants as you go.

Shelley:
Ooohh well you know I think I read about that and they said if you were a smoker, if you were going to go out and deal with your tomato plants, wash your hands.

Brian:
Wash your hands before you handle any plant material. Typical symptoms of this virus on something like petunia, a lot of blotchy leaf color.

Shelley:
Kind of unhealthy looking.

Brian:
Yeah, kind of light and dark. Random patterns in the leaves, this is a symptom called mosaic. We also tend to get a fair amount of stunting with this particular virus also, so not a happy plant. A lot of leaf distortions, so we got lots of plants that look not their normal shape or size.

Shelley:
So, not healthy.

Brian:
Not at all.

Shelley:
Well now this one, this one you said kind of made you happy.

Brian:
Yes, I like this symptom because it's very distinctive and for a plant pathologist, doing diagnostics it's nice to see something that you can say hey that looks like a virus problem.

Shelley:
And you know it's exactly what it is and it's easy.

Brian:
Well you never know exactly quite what it is, but I can always guess. This sort of ring pattern is very typical of a virus called impatient necrotic spot virus. It's a thrips transmitted virus.

Shelley:
Which is an insect.

Brian:
A little tiny insect that we oftentimes see--we can see it afterwards but it's really a problem in greenhouse production and the insect picks up the virus and when it feeds it drops it off and usually around the point where the initial infection occurs you get these kind of concentric rings.

Shelley:
Ahhh, so each one of those spots is where the thrip ate.

Brian:
Probably where the thrips ate, yeah.

Shelley:
Oh cool.

Brian:
That's right. And then on this post the virus seems to have stayed relatively near where the infection occured, but it can on other hosts like impatients go systemic which means it gets spread throughout the plant.

Shelley:
The entire plant is diseased.

Brian:
Yes, yes. That's right and then what you tend to get as in this particular plant is a stunting. These plants should probably be about 6 or 8 inches tall.

Shelley:
This isn't a groundcover.

Brian:
No it's not a groundcover, it's not a dwarf variety. The other thing you'll notice, again a little bit of blotchiness in the color but also very distored looking leaves. They're small, they're misshapen, just not a very thrifty looking plant.

Shelley:
So, and I know from working in a greenhouse, thrips are a problem there. We don't want to bring these--we don't want to bring thrips into our houses as just a home gardener.

Brian:
Yeah, really bad news if you bring a plant like this into your home and you had orchids because you could end up causing a problem on your orchids.

Shelley:
And who knows what else. So, plants like these we get rid of.

Brian:
Typically I would suggest throwing them away; you could certainly try to compost them. I wouldn't necessarily do that with this particular plant with the tobacco mosaic. But something like the impatient necrotic spot, compost it as long as you're hot composting.

Shelley:
So, a mediocre composter, throw them in the garbage.

Brian:
Throw them in the garbage and get rid of them that way.

Shelley:
Now this is one that I'm intrigued with because you said you didn't know what it was.

Brian:
No, it is virus infected, and you can tell because of these relatively distinctive sort of line patterns on the leaves which I think are very very attractive quite frankly but this plant is very likely infected with a virus. If I really wanted to knwo what this one was I would send this plant off to a lab in Indiana that basically specializes in virus testing. But for us, if we want to test for something like impatient necrotic spot virus, we actually do have inhouse tests for that.

Shelley:
I was just going to ask you. So, how do we know what we've got?

Brian:
Yeah, these are tests that are basically based on the same technology as a pregnancy test. And what you do is take a little bit of leaf tissue and put it in this bag that has liquid in it. It's all pre-packaged. Then you put a little dipstick in it and it sops up the liquid, and if you get two little lines like you see here, you know you have a particular virus in that tissue. If you get only one red line, there's no virus, at least not that particular virus present.

Shelley:
Now this is something you do for us unlike a home pregnancy kit.

Brian:
That's right, that's right, those are the test we can do in my lab.

Shelley:
Ok, well and then you said this is the virus de jour.

Brian:
Yeah, kind of the one that people are really talking a lot about. It's hasta virus acts on hasta, and this particular virus again is mechanically transmitted, and you can--

Shelley:
By the hands?

Brian:
By the hands, you could certainly move it that way, using tools as well if you're dividing hastas, you can move it around that way. Some reports of mowers or even weedwackers getting it on the wires of weedwackers and then moving it from plant to plant. Typical symptoms are almost kind of a searsucker pattern, almost pitty on the leaves.

Shelley:
So that's not part of the breeding for this one.

Brian:
Not part of the breeding for that particular Hosta. Also this kind of blotchy light and dark discoloration, particularly kind of bleeding off of the veins is very typical as well.

Shelley:
Ok, well you've reassured us that none of these are really probably going to kill our plants but as a home gardener, we don't want something that's just laying there not really producing anyhow, so we get rid of them, we compost, or garbage.

Brian:
Right, the other reason to get rid of them is so that you don't spread the virus to other plants in you yard.

Shelley:
Make is worse.

Brian:
Right, make it worse.

Shelley:
So, what do we do?

Brian:
Wash the hands, get rid of the plants. The other thing would be just to be very careful with your tools, you want to clean those, and usually we recommend with using a combination of shampoo, about 5-10% in water and then some detergent as well, and then using that to clean your tools.

Shelley:
Ok, so and practice good gardening procedures, don't crowd things.

Brian:
Exactly, that's right because mechanically transmitted viruses can be transmitted through plants just leaning and touching, rubbing against one another.

Shelley:
So, and if we think we have something that is a problem, you're the guy to contact.

Brian:
That's right.

Shelley:
Ok, thanks Brian.

Brian:
You're welcome.

Shelley:
Next up we'll give you Brian's website, http://www.plantpath.wisc.edu/pddc/.