Tan Spot On Wheat
The fungus Pyrenophora tritici-repentis.
Tan spot lesions on leaves characteristically have a small, tan to brown center, which is surrounded by a yellow circular border. As leaves mature, lesions expand, kill tissue, and can impart a tannish hue to leaves. Lesions, which initially are found in late winter or early spring on lower leaves, result from infection by spores released from fruiting bodies that formed on wheat residue left in the field after harvest.
Cultural practices, variety selection, and fungicides can be used to control tan spot. Clean tillage and crop rotation facilitate destruction of residue, which reduces inoculum present to start the disease. Fungicides (consult with your county extension agent or the current edition of the OSU Extension Agents’ Handbook of Insect, Plant Disease, and Weed Control) can be applied to prevent infection and spread of tan spot, but rarely would this be economically beneficial in Oklahoma. Some varieties are more resistant to tan spot than others. If tan spot is a concern, consult with your seed dealer, extension agent or information such as the, "Wheat Variety Comparisons Chart, 1997," Production Technology - Crops, July, 1997, vol. 9, no. 17 (revised) to identify varieties resistant to tan spot.