Apply every other day in southern Missouri. Follow label directions on total material per acre per season. Powdery Mildew in the Fall Landscape Timothy P. Baker, Horticulture Specialist Powdery mildew is a common problem throughout the growing season, but it often plaques our gardening efforts to a greater degree in the late summer and fall. This fungal disease appears as a light grey, powdery material growing on the leaf surface. Although it is common on many ornamental plants, powdery mildew can affect a wide variety of plants if the conditions are right.
Many fungal diseases require free water on the leaf to infect the plant.
Powdery midlew usually needs only high humidity. The cool nights of fall, combined with warm days, provide optimal growing conditions for this disease. If you have had a problem with powdery mildew in the past, there are several thing you can do to help your plants avoid this disease. First, don't place your plants too close together. Closely-spaced plants have poor air circulation, which results in a higher humidity and favorable conditions for mildew.