Powdery Mildew: Identification and Treatment to Protect Your Tree

By Canopy Team on September 10, 2021

With warm days and cool nights, the Midpeninsula weather is often ideal for Powdery Mildew to infect your trees and plants.

What is Powdery Mildew?

Powdery Mildew is a group of diseases caused by fungi that infect leaves, buds, flowers and/or stems. First appearing as small, white or gray, circular patches on plant tissue, it spreads rapidly to form powdery areas of fungus. In addition to white or powdery substance on leaves, some curling or wilting may happen as well.

Each species of powdery mildew only infects a small variety of plants, but unfortunately, there are over 11,000 types. Powdery Mildew is commonly seen on trees such as London Plane (Platanus x acerifolia), Crape Myrtle (Lagerstromeia spp.), and Valley Oak (Quercus lobata).

Will my tree die?

Powdery Mildew rarely causes the death of a tree, however, it can cause some dwarfing, discoloration, and even dieback (see picture on right). Although it’s mostly an eyesore, it should be treated, because it can cause stress and other issues. New growth may be stunted, and blossoms may fail to set fruit or may produce fruit covered with fungus.

How can I treat Powdery Mildew?

There are a few solutions. 

  1. Prune off and dispose of the infected areas. Summer is not the best time to prune many of these trees, so a second option is to…
  2. Thin out affected trees during the winter months. Thinning out the trees helps create good air circulation, which will keep the fungi from coming back.
  3. Treat with a foliar spray using baking soda (1 tablespoon), water (1 gallon), and dish soap (1 teaspoon). Spray on the affected areas and wipe off with a paper towel or rag. 

For additional information about your tree’s specific needs or for help treating your tree, check out Canopy’s Tree Library or find an arborist through our online Arborist List.

Source: Missouri Botanical Garden

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