Phyllosticta Leaf Spot (Phyllosticta spp.)

From: Ostry, Michael E.; Wilson, Louis F.; McNabb, Harold S., Jr.; Moore, Lincoln M. 1988. A guide to insect, disease, and animal pests of poplars. Agric. Handb. 677. Washington, DC: U.S. Department of Agriculture. 118 p.

Importance- Infection reduces photosynthetic area of severely diseased leaves. Premature defoliation can weaken small trees.

Look For: Small brown spots on upper surface of leaves in spring. White-gray blotches with black fruit bodies (pycnidia) scattered within the affected areas in midsummer to late summer.

Diseased leaf Photo by: USDA Forest Service - Rocky Mountain Region Archives

Biology- The fungus overwinters on infected, fallen leaves. Pycnidospores are rainsplashed to developing leaves in the spring. Secondary infections are caused when pycnidiospores produced in infected areas are rainsplashed to adjacent leaves later in the summer. Disease is most common and severe where air movement is restricted such as in closely spaced plantings where moisture is retained for long periods on leaf surfaces.

Control: Direct control is usually not needed. Wider tree spacings and removal of infected leaf debris before spore release in the spring will reduce disease

Fruit bodies within leaf spots.

For Additional Information:

Ostry, M.E. 1980. How to identify Septotinia and Phyllosticta leaf spots of poplars. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 6 p.