Gardening Expert Issues Warning About Downy Mildew

PITTSBURGH (KDKA) - If you held off on planting for the summer last weekend because of the frost advisory, there's something else you need to watch out for when you do plant.

Specifically, you'll need to look out for a fungus with a fondness for a certain flower.

The battles of impatiens with downy mildew have received national attention for several years.

"We have had two bad seasons as far as wet and cold, and so wet and cold means fungal issues and downy impatien mildew is a fungal issue. So, we are not even sure we are going to get the disease. It depends on the weather," Pittsburgh Post-Gazette garden contributor Doug Oster said.

While many are just now planting the wildly popular shade-lover, it's good to know nurseries in Florida are making great strides to ensure there are vibrant plants at your local garden center.

"One year, we had plants that came up from the south that were already infected. That was the worst year that we had. So now they are really taking care to make sure that no plant you get at the nursery is infected with the disease," Oster said.

Downy mildew is a fungus and one that only goes after one particular flower.

"If you have got any other types of plants, you don't have to worry. It is just focusing on this type of impatien. And as I said, it's been around since the 1800's. We don't know why it's become such a problem, but we think it's a combination of weather and that first year that we had some that were shipped up here with the disease," Oster said.

Historically, the airborne downy mildew spores don't get here until the end August, but you can keep it out of your flowerbed by keeping a close eye on the forecast.

"If you have impatiens out there and were getting a period of cold wet weather, treat them with an organic fungicide like Serenade, that's the one I love," Oster said.

Serenade is organic meaning it can't hurt us, but it effectively kills the airborne spores to keep the disease from reproducing. Here's another suggestion to keep your impatiens healthy.

"Don't plan impatiens in big drifts. Split it up with different plants so in case the disease does manifest itself, you may just have one little area that gets affected," Oster said.

If you don't spray and your plants do get downy mildew, there's frankly nothing you can do.

"Once the plant show signs of disease, that's it, and what happens is it basically drops all of its leaves and flowers and it will just look like a skeleton. When you see that, there is no hope for it," Oster said. "You want to pull it out root and all, and basically you can't compost that now. You either are going to bag, or burn or bury it."

If you don't want to worry about the fungus, there are new hybrid varieties called New Guinea impatiens that eliminate the problem. They look similar with some subtle difference.

"It's a different species of impatien and immune to the disease. It doesn't look quite the same. It takes more sun than our regular impatien, but it's a great substitute as are other great shade lovers too if you are afraid to plant you regular impatiens, there are lots of great shade lovers that you can put in," Oster said.

But by following these helpful hints, Oster plans to plant his impatiens this week -- same as always.

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