Gail Ruhl, Plant Disease Diagnostician
Tubakia leaf spot (formerly called Actinopelte leaf spot) is a common late-season fungal leaf spot disease of trees in the red oak group (such as pin oak and red oak). Symptoms include small to large dark brown or reddish-brown spots or blotches on leaves. Tubakia leaf spot can cause early defoliation of heavily infected oaks, but the disease usually develops late enough in the growing season that no adverse effects on the health of the tree occur. This year, however, the disease may be contributing to decline due to extreme drought conditions. As always, proper maintenance of trees to reduce root stress will help invigorate overall tree health. The best management for these stressed trees is to thoroughly water (1 inch per week) during dry periods and fertilize appropriately. Detailed information about proper fertilization is available in Purdue's Extension publication, HO-140 Fertilizing Woody Plants Plants.
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Plant and Pest Digital Library Project, Purdue University, West Lafayette, Indiana.