Leaf diseases such as peach leaf curl, apple scab, and anthracnose are very common this spring. The cool wet weather was perfect for fungal infection and disease development. Peach leaf curl, caused by the fungus Taphrina deformans, produces leaves to become thick and puckered with a red or purple hue. As the disease progresses, a grayish powdery film of spores forms on the leaves. Deformed leaves turn yellow or brown and fall from the tree. When symptoms are apparent it s too late to control peach leaf curl. Fungicide treatments are effective in the fall after leaf drop or in the spring before buds swell. Several fungicides, including Bordeaux mixture, liquid lime sulfur, chlorothalonil, and copper hydroxide are effective for peach leaf curl management. Removing plant material, including infected leaves, fruit, and twigs by raking and pruning can reduce the potential for disease next year.
Apple scab, caused by the fungus Venturia inaequalis, results in black spots on leaves. Infected leaves eventually turn yellow and fall prematurely. Severe fruit infections can cause the skin to crack open resulting in deformation. Fungicide applications may not be necessary for disease management when springs are dry. However, when the weather is cool and moist, treatment on susceptible trees may be warranted. Proper pruning can improve ventilation to help dry leaves. Raking can aid in removing the potential overwintering fungus. Resistance is the best method for apple scab management.
Fungicide application for susceptible cultivars is recommended before bloom and should be continue through the growing season at regular intervals. Chlorothalonil is one of the fungicides that can be used for this disease.
Anthracnose symptoms are apparent on white oak, ash, sycamore, and maple. Leaves are distorted and leafs have dark brown areas. Some anthracnose fungi can cause early loss of leaves. Fungicide use on established shade trees usually isn t necessary. Trees typically recover by late spring when new leaves flush out. Fungicides labeled for injection into sycamores can be helpful, but the injected holes drilled into trees can open entry ways for decay organisms.
This article originally appeared in the 6/6/2003 issue.