Curing Powdery Mildew - Knowledgebase Question

Atlanta, GA
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Question by rsaag
June 21, 2005
Is there any way, preferably not involving chemicals, to cure powdery mildew on my plants? I've done my best to give them enough room and water, but it still occurs on just about every plant in the gardens. I have quite a few rare and hard-to-find varieties, so I'd accept just about any solution. If I simply left the powdery mildew and did nothing about it, could it do any harm to my plants?

Answer from NGA
June 21, 2005
Powdery mildew can eventually defoliate and kill plants. The bad news is that this fungal disease overwinters on living plants, and can be difficult to eradicate. There's some good news, though. First of all, specific strains of the mildew affect different types of plants, so, for example, the powdery mildew on squash won't spread to your perennials. Also, plant breeders have developed powdery-mildew-resistant varieties of many types of plants, so consider this when choosing new plants. There are some things you can do to minimize problems with powdery mildew. This disease is unique among plant diseases in that it doesn't require a wet leaf surface to spread. It can thus thrive during hot, dry weather. The general advice to inhibit the spread of fungal diseases is to avoid wetting leaf surfaces. In the case of powdery mildew, however, you can actually inhibit infection with periodic strong sprays of water (not so strong as to damage the plant.) Here are some general rules for control. Start by making sure that your plants are getting enough direct sunlight. (Eight to ten hours a day is generally the minimum for plants that flower or bear fruit.) You'll also want to make sure that there's enough room between plants for air to circulate freely. Overcrowding not only makes plants more susceptible to diseases, if leaves touch other plants, those diseases can easily be spread. Some people report success with this home-made spray: Mix 1 tablespoon of baking soda and 2 1/2 tablespoons of ultra-fine horticultural oil in a gallon of water. Apply as a spray as soon as the mildew appears and every 10-14 days thereafter. Be sure to coat all surfaces.

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