When Downy Mildew Strikes

Impatiens Downy Mildew has now reared its ugly head in the Midwest so it’s time to learn about this disease, what to do about it, and what to tell your customers who have questions.

Downy mildews are not uncommon diseases on ornamentals, but the impact of Impatiens Downy Mildew has been greater than most in the areas that have been affected. Thankfully, the pathogens that cause these diseases tend to be very host specific so only one plant species is infected.

Spring and fall are periods when the disease is most likely to develop because Impatiens Downy Mildew of the cool, wet/humid weather. Initial symptoms can include off-color, light green leaves with a stippling. Infected leaves often curl down and the undersurfaces of leaves can have a white, downy growth. Younger tissues are especially susceptible to infection, so symptoms are often first observed on the terminal growth. Stunting and reduced flowering can result, followed by leaf and flower drop, stem collapse and, in severe cases, plant death.

·  Use a wide range of herbaceous ornamentals in your garden to limit the spread of disease and the impact of plant loss.

·  Consider using alternate plants. New Guinea impatiens and Sunpatiens appear to be immune. Alternanthera, Begonias, Coleus, Euphorbia,Geraniums, Ipomoea (sweet potato vine), Iresine, Salvia, and Torenia are other good alternatives for shady spots.

·  Do not plant impatiens in the same location each year because the impatiens downy mildew organism spores can survive in the soil

·  Space plants far apart in the garden to allow for good air movement even when grown to full size.

·  Work in potentially contaminated beds last to help prevent spreading the disease as you move from bed to bed.

·  Clean and decontaminate garden tools by rinsing them with a strong stream of water followed by either 70% alcohol (preferred for metal) or 10% bleach solution for at least 30 seconds to complete decontamination.

·  Do not water overhead or with a sprinkler to minimize water on the leaves.

·  Remove infected plants immediately to limit the spread of the disease to other plants. Put the plants in a sealed bag in the garbage; DO NOT compost these plants.

More information is available at the following sites:

http://www.ipm.iastate.edu/ipm/hortnews/2012/6-27/mildew.htm

http://www.extension.iastate.edu/article/yard-and-garden-impatiens-downy-mildew

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