Plant mildew usually comes in a powdery form that gathers on the leaf surface. This disease usually affects trees, but shrubs can also be affected by this "powdery mildew." The powdery substance is actually millions of tiny fungal spores that are spread by air currents from one tree to another.

While a little fine powder on a leaf might not seem alarming, powdery mildew can stunt new growth. New growth on a tree infected with powdery mildew may be small and covered with mildew. These new growths will probably be curled and new buds may fail to open. The powdery mildew fungus germinates best in very humid conditions, but severe outbreaks are most likely to occur in dry climactic areas, where spores are more likely to be spread by winds.

You can prevent powdery mildew with smart planning. Proper placement when planting trees is essential to tree health. Most fungi proliferate where trees are very close together, which creates a moist, cool harvesting ground. Try to plant trees accordingly and remember to prune the trees and remove any fallen leaves, which create a host for fungi. Try to keep lower branches thinned, as they can provide a cool moist place for fungi to grow.

Treatment

Fungicides are available to combat powdery mildew once it has appeared. Frequently treating trees that have or have had a fungus problem will help to keep the mildew in check. If you maintain a frequent treatment schedule, you should be able to avoid more drastic measures, such as chemical treatments or destroying the tree.