Leaf diseases can occur in warm, moist conditions, especially when plants lack space for adequate air circulation around all sides of the plant. In some situations, removing the affected area by making a cut about 6 inches into a healthy plant stem may be all that is needed to eliminate the infection. Identifying leaf diseases can help determine the proper care needed to eradicate the disease.
Leaf spot displays as a round, dark spot on the leaf. The spot may be bull’s eye shaped, with a dark center and a light perimeter. Leaf spot can be caused by a fungus that spreads through spores. Many trees, shrubs, flowers and vegetables can be affected by leaf spot, especially when planted too close together. Cut out affected leaves and apply a fungicidal spray to help control leaf spot.
White, fungi spores give the appearance of powder on a leaf. In early stages, powdery mildew can appear as small, irregular blotches on the leaf. Powdery mildew can affect trees and shrubs. The spores can spread on the wind or when rain hits the spores on a leaf, splashing the spores to another leaf. Cut out affected leaves and apply a fungicidal spray to help control powdery mildew.
Sooty mold can affect the leaves of trees, like maple or elm, when the trees are in a shaded area. The mold, which will not harm the trees, is a black fungus that grows on the secretions of sap-eating insects like aphids. A blast of water from the garden hose can wash aphids from leaves and prevent the growth of sooty mold.
The verticillium fungus can cause leaves to wilt and fall off. Sometimes, the leaf color will lighten and the leaf will fall off without wilting. Pruning out affected branches along with proper fertilizing and watering may be the best control for verticillium wilt according to North Dakota State University’s agriculture extension.
Rust can affect leaves, stems and the fruit of plants. Rust disease gets its name from the orange to reddish-brown color of flecks or large blotches of the fungus. Rust can affect trees like the crabapple or flowers like the snapdragon. Prevent rust by controlling water spray. Early morning watering will provide time for moisture to evaporate from the foliage and fruit with an assist from the sun. Cut off and dispose of affected areas. A fungicidal spray may also help.
Each county of every state in the U.S. has cooperative extension system (CES) offices as part of a USDA program. Often overseen by local universities, highly skilled volunteers, trained in growing and caring for vegetation, can answer questions for county residents. You can contact or visit you’re your local CES office for assistance in identifying and controlling plant disease. To find the CES office in your area, click here.
Sources: North Dakota State University; Ohio State University Extension