Do not allow lawn sprinklers to wet aspen foliage. Remove leaves in the fall to reduce inoculum. The most common symptoms are premature defoliation and witches'-broom caused by twig and shoot blight. Lesions can develop on sycamore leaves. The fungus overwinters in twigs and branches and then infects the following spring and early summer.
Control is difficult.
Pruning has very little effect. Fungicides must be applied in the spring when buds are swelling. Powdery mildews are widespread throughout the landscape now. These fungi are host specific - that means the mildew on apple will not spread to honeysuckle or lilac. These are usually more of an aesthetic problem than a health problem.