Photo courtesy of Michigan state university

Greenhouse Management: What does the process of putting something like this e-Gro together — with different components involved — look like?

Jan Byrne: Roberto, he did the majority of the work on it [in this case]. And so, what happens is something comes in like powdery mildew on succulents and the symptoms on that can be a little bit confusing because it’s not what you and I think of as really obvious powdery mildew symptoms. So we asked for samples that came into the lab relatively recently and, at the same time, my understanding is that Roberto was growing plants in his research greenhouse that also had the same symptoms. So I was working on these samples, he was doing his thing and we thought it would be helpful to write an article about this aspect of powdery mildew and how it can cause this scarring.

GM: What are the symptoms of powdery mildew on succulents that make it different than the more commonly recognized symptoms?

JB: On succulents, powdery mildew does not spore readily. So you don’t always see that white powdery look — what we think of typical powdery mildew symptoms. Instead, you see this kind of corky scarring or scabby-like lesions that are produced on the surface of the leaf. There are some pictures in the e-Gro that really highlight that and show how different it really looks. In the past, I’ve seen it on kalanchoe a few times a year and some others — enough to know when I see something on one of these newer succulents that I haven’t done a lot of work on, it’s enough to think that it’s a possible suspect that should be considered.

GM: When you start work on a problem like this and collaborate with other researchers, what does your work process look like?

JB: It’s nice to have some kind of background and familiarity with the host, which isn’t always the case with what I call “new” succulents that are becoming more popular. Without that background, a plant will come in, you try to get a feel for what the host is, as well as what you need to know about what’s normal versus not normal. Sometimes it’s not always clear why a grower has submitted a sample. A lot of times, my next step is to take some of that plant material and go to dissecting it under a scope. There, I can look with some magnification at the symptoms — say those scabby lesions — or there may be insects present. If that’s the case, I can have my colleague Howard Russell pursue that avenue. I can also use a different scope with more magnification once I get a better idea of what I’m looking for. If that doesn’t reveal anything, then I might start pursuing other possibilities like viral pathogens and/or consider that it might not be a disease pathogen at all.