Powdery Mildew

Powdery mildew is an obligate parasite.  Huh?  In short, powdery mildew doesn’t want to kill your plants – but it sometimes happens, by accident of course.  We most often see this disease on plants outdoors where there is poor air circulation.  You probably have seen peony bushes around town or even your own that ended the fall heavily infested with powdery mildew.

What makes this disease unique is it’s ability to move quickly into an epidemic stage.  The spores (conida) only need high humidity and no free water on the leaf surface to germinate.  This allows the disease to rapidly spread across the leaf surface covering it with the traditional white film.

Plants that tend to be prone to powdery mildew should be treated with a fungicide such as propiconazole, chlorothalonil, or myclobutanil.  All three of these active ingredients are found in most fungicides available to homeowners (always read and follow the label instructions).  Good sanitation will help remove spores that will overwinter in debris.  Improving air circulation along with water & nutrient management will help.

But what can you do for indoor plants?  African violets are very susceptible to powdery mildew.  The picture in header of this blog shows an African violet with the initial stages of powdery mildew on the flower petals.  One of the best management tools is a fan.  Improving the air circulation will reduce the likelihood of occurrence.  Fungicide options are limited for indoor use and options include neem oil, Physan 20 and Consan 20.  The last two are disinfectants that will help kill spores on the plants (read and follow the label instructions).

Another novel approach to help cure powdery mildew is to wash it off the plant.  This disease can actually be inhibited by water on the leaf surface.  It’s something to think about if you are trying to stay away from using pesticides.

This weekend is suppose to be nice so after you are done shopping get out in the yard and make sure that any plants that had a disease are removed from the flower/garden area.  Indoor plants would appreciate a ceiling fan or even a small oscillating fan to move the air around.

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Powdery Mildew on peonies
Scott Evans
Scott Evans is a horticulture assistant with Nebraska Extension in Douglas-Sarpy Counties. A certified arborist through International Society of Arboirculture and Nebraska Arborist Association. Scott is also Tree Risk Assessment Qualified through ISA. Scott co-leads the Master Gardener program in Douglas & Sarpy counties. Along with volunteer management he provides his expertise with disease and insect identification, lawn and landscape weed management, plant health, and I.P.M. practices. He also enjoys growing many houseplants ranging from African violets to cacti and succulents. Scott has two Bachelors of Science, one in Biology (emphasis in Botany, Ecology and Environmental Science) and second in Environmental Geology from Northwest Missouri State University. He earned his Master of Agriculture from the University of Nebraska-Lincoln.

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