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. Pruning to increase air flow can reduce mildew problems. Also, be sure sprinklers are not wetting the foliage. Fungicides can be used in extreme cases.