The following is information on current diseases in the landscape from Bob Mulrooney, Extension Plant Pathologist, UD.
This is turning out to be an exciting year for plant pathologists--diseases springing up everywhere (pun intended). Look for scab, frog-eye leafspot and cedar-apple rust (bright orange lesions) on susceptible crabapple cultivars. Frogeye or Phyllosticta leafspot on red maple, silver maple and boxelder (irregular tan spots withred-brown margins--a minor disease rarely requiring control). Anthracnose, booming due to the cool wet weather can be found on sycamore, ash (same fungus causes anthracnose on Chinese fringe tree--look for curled, deformed leaves or leaflets and brown necrotic areas), even on oak leaves in the understory (producing large brown blotches and small irregularly shaped spots). Each host has its own specific anthracnose fungus. These diseases are usually not serious enough to warrant fungicide control.