Powdery Mildew (Garden Diseases)

Powdery Mildew (Garden Diseases)

Part of Ep. 704 The Summer Garden

Learn how to tackle powdery mildew.  Plant pathologist Brian Hudelson explains which plants are susceptible to the disease and how to get help from the UW-Extension.

Premiere date: Aug 28, 1999

TRANSCRIPT+
Wisc Gardener Transcript: 

Shelley:
You know, over the years I feel I've gotten pretty good at handling insect problems in my garden. Now, diseases are another matter. Maybe it's because there are so many of them. For instance, this book contains just the fungal diseases that can affect plants. And there are many other problems. I'm with plant disease diagnotician, Brian Hudelson. Brian is with the University of Wisconsin Department of Plant Pathology. Brian, thank you for joining me.

Brian:
Thanks for having me.

Shelley:
With diseases, where does a home gardener start when there's so many out there?

Brian:
It's really very, very difficult. There are so many diseases that are out in your yard on your plants that it's virutually impossible for those homeowners really to get a good diagnosis of their disease problems. But there are some exceptions. What we're going to be talking about this morning is one, I think, that homeowners really can get a handle on and diagnose on their own plants. It's called powdery mildew. And powdery mildew-- this certainly is not an ornamental plant, it's a weed-- but the symptoms that we see on the weed are very, very similar to what we'd see on other plants. It looks like someone has taken some talcum powder or some powdererd sugar and just sprinkled it over the surface of the plant.

Shelley:
Yeah, it's spotted all over the place. Is this something that all plants can get, or any plants can get?

Brian:
I'm really hard pressed to think about a plant that doesn't get powdery mildew. Most of the common ones that we deal with normally will get powdery mildew. That includes both outdoor plants and some indoor plants.

Shelley:
Are some more susceptible than others?

Brian:
Yeah, and the outdoor are the ones that I normally think about in terms of having powdery mildew are minardas and phloxes, and also lilacs-- the shrub that most people will mention to me when they think about powdery mildews.

Shelley:
What about house plants?

Brian:
Inside, you can get powdery mildews as well. Ones that I normally will see powdery mildew on are thing like african violets and also begonias.

Shelley:
By bringing in this diseased plant, have we just infected this entire area?

Brian:
No. Fortunately, that's not the case. Powdery mildews are caused by fungi. There are many different fungi. They are all very closely related, but they tend to be relatively specific. So, the fungus that causes the disease on the weed is not necessarily the same one that causes the disease on other plants.

Shelley:
It's different on each plant. So, I don't have to worry.

Brian:
No, but-- Yes and no. You don't have to worry that it's the same fungus, but what you do have to worry about is if you start to see powdery mildew is you've got really good environmental conditions for the development of the disease. That usually means high humidity.

Shelley:
That means summer in Wisconsin.

Brian:
Summer in Wisconsin is perfect for powdery mildews. We see a lot of them in the state.

Shelley:
Hot, moist, humid...

Brian:
That's right.

Shelley:
We can get those conditions indoors, too.

Brian:
You can get them indoors, too. We get them in the summer indoors, but we can also see it in the wintertime as well. Particularly if people have a lot of houseplants that they're crowding very close together. So, you get a lot of localized high humidity around those plants.

Shelley:
So, if we see it, I assume it's time to really panic.

Brian:
No, really not. The disease is particularly severe on this weak plant, it does look awful. But on a lot of plants, I really think of the disease as being primarily a cosmetic disease. It makes it look a little bit crummy, but it's not easily that bad. For example, this is a grapeleaf ivy that has powdery mildew, but you really can't tell it that well. There's a leaf right here that has a problem.

Shelley:
So, it is really cosmetic.

Brian:
In this particular case, it might get a little bit more severe and you might get some defoliation. But at this point, it's pretty much cosmetic.

Shelley:
Are there any plants that can be killed by this?

Brian:
The ones I think of are some of the outdoor plants, again, phlox and minarda. They can get it so severely that eventually they will defoliate.

Shelley:
Which isn't good.

Brian:
Which is not good. But there are some things you can do if you're having problems. One of them is to-- particularly with things like phlox-- look for varieties that are resistant to powdery mildews. Those are commercially available. It doesn't necessarily mean you won't ever get powdery mildews on those plants.

Shelley:
But you can minimize it.

Brian:
That's right. Another thing you can do-- I usually recommend cultural practices that will be effective. And what that really means is spacing your plants far apart so you get a lot of air movement. That will reduce the humidity. Also, if you're using a lot of water, if you're watering a lot, cut back a little bit. Stop it, basically, because that will increase humidity around your plants. Also, if you've mulched and that's really wet, you might want to spread that out and let it dry a little bit, again, reducing water around the plants.

Shelley:
If it looks like we have a really bad infestation, can we start using the fungicides?

Brian:
There are fungicides that are available. You can buy them at your local gardening store. I usually recommend that as kind of a last resort. And I also typically recommend that if people are going to be using fungicides, that they contact their County Extension agent before they do that to get information on what products are available and how to use those products.

Shelley:
The County Extension agents are really kind of our forerunners or front runners for any disease problems, too.

Brian:
That's right. If you're having a disease problem and need to get a diagnosis, I would take a plant sample into your County Extension agent. They're very knowledgeable and lots of times tells you what your disease problem is right in their office. If they're having problems, they can forward the sample to my lab. We have a for-fee service. For a small fee, you can send your plants to my lab and we'll diagnose the problem for you and send you the diagnosis and information on control.

Shelley:
Great. Thanks, Brian. Get something to write with and we'll give you more information about getting your diseased plant materials to Brian Hudelson.

Shelley:
We forgot to talk about my favorite summer garden activity: sitting in the shade and watching somebody else pull the weeds. If you'd like more information about any of the topics we discussed today, be sure to check with your local County Extension agent. I'm Shelley Ryan. Thanks for joining me on "The Wisconsin Gardener."

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