Orchid Care from the American Orchid Society
Late Blight on Tomatoes and Potatoes
***Impatiens Downy Mildew***Impatiens Downy Mildew***Impatiens Downy Mildew***
We've started seeing the effects of Downy Mildew in local impatiens beds recently. This plant disease affects all impatiens with Impatiens walleriana breeding. This means, the typical bedding plant impatiens and double impatiens will get this disease. New Guinea Impatiens and Sunpatiens have different breeding and are highly tolerant of this disease.
Downy Mildew infections are difficult to identify in the early stages. You may notice a few yellow leaves with green flecks, sometimes the leaves will curl under as though the plants are thirsty. The most obvious sign of infection is the production of white spores on the underside of leaves. These spores are dispersed through water and by the air. Eventually, infected plants lose all leaves and the remaining stems wilt to the ground.
It is possible to prevent infection of impatiens within the greenhouse, but prevention is much more difficult in the landscape. There is no cure once the plant in infected. Spores are able to overwinter for several years (the exact length of time is, so far, undetermined), so if you have seen indications of the disease in your beds, do not plant I. walleriana-type impatiens there next year! You should also bag and dispose (do NOT compost) any infected plants, including any susceptible impatiens within a 3' radius. The disease which causes Downy Mildew in Impatiens is not the same variety that you'll occasionally find on other bedding plants, so your other plants in the same bed as infected impatiens will remain unaffected.
So far this year, the disease has not been aggressive due to the hot, dry weather central New York has been experiencing. Now that we have seen some fairly heavy rainfall and the temperatures are cooling off, the disease will spread and become more obvious.
What does this mean for your impatiens beds next year? Well, you'd be wisest not to make them impatiens beds next year - or at least you should switch to New Guinea Impatiens or Sunpatiens. Some recommended substitutes for impatiens include begonias, coleus, lobelia, and torenias, among others.
Containers, planters, or hanging baskets are still okay to plant impatiens in, so long as the soil is removed (bag & dispose - NO composting) and the containers disinfected before planting next year. Because Impatiens Downy Mildew is also dispersed on the wind, it is possible for containerized plantings to become infected despite the use of new soil and disinfected containers, but if you water your planters in the morning, allowing the leaves and stems to dry within a few hours, you may be able to prolong the life of your containerized impatiens.
You can find some images of infected impatiens here, to help you determine if your plants have Downy Mildew.
And here's a press release we've sent out to local media this fall.