As the galls age, they turn brown and degenerate. Flower parts may also be affected. When this disease is severe it may reduce vigor of the plant due to the loss of young leaves, but is usually a cosmetic disease, only affecting the appearance of the infected plant. Factors Affecting Development Leaf gall is usually most severe on plants growing in very shaded locations or in locations where air movement is restricted and evaporation poor. The disease is seldom a problem during dry springs or when plants are in sunny locations.
Infection occurs when moisture is ample.
Once the disease appears, there is no practical method of control except to pick off and destroy the infected plant parts. This is possible where only a few galls are present on the plants. This reduces the source of spores and may provide adequate control of the disease. In situations where gall removal is not feasible, the disease can be prevented by proper timing of fungicide sprays to protect new growth in the spring. Be sure to check labels for rates and precautions.