Black Mold in a Garden

Identification

• Black mold is a fungus that grows on the surface of the host plant. This velvety fungus is easy to rub from affected leaves, but soon returns. Certain species of plants are more susceptible to black mold, such as apple, crabapple, maple and willow trees. Black sooty molds can also grow on non-living surfaces, such as sidewalks, driveways and fences that are close to infected trees.

Effects

• Black mold grows on leaves, needles, shoots, buds and flowers of affected trees. Heavily infected trees and plants often yield smaller fruit, are pale in color and produce new shoots that are smaller than normal. While black sooty mold is considered a cosmetic problem, it can have adverse effects on trees with heavy coverings of mold due to a lack of sunlight. Plants with black mold often wilt easily and have reduced vigor, especially under drought conditions.

Cause

• Black mold on garden plants is caused by insect infestations. Certain types of insects, such as mealybugs, aphids, scales, psyllids and whiteflies, excrete a sticky substance known as honeydew, which causes black mold to stick to the affected plant or tree.

Control

• Controlling insect infestations in your garden is key to controlling black mold in garden plants and trees. Spraying your plants with a hard stream of water three times a week can eliminate insects by washing them from the tree leaves. Applying horticultural oils can smother insects and eliminate them. Insecticides approved for the control of sucking insects, such as aphids and scales, are available at your local garden center. When the insects are under control, black mold is reduced.