Flag Smut

Symptoms
Leaves are twisted laterally, giving the appearance of hormone-type herbicide injury, and heading may be prevented. Diseased plants are stunted and produce excessive numbers of tillers. Usually systemic, the infection normally affects all tillers. Occasionally, only isolated tillers are affected. At or near heading, long, gray-black streaks develop between the veins on the leaf blades and sheaths (Photo 7). These streaks, the smut sori, have a greasy appearance. The sori split open to release the teliospore masses, resulting in ragged, tattered leaves.

Cause
Flag smut is caused by Urocystis agropyri (synonym U. tritici), a basidiomycete. The fungus forms small spore balls consisting of 1 to 4 teliospores surrounded by a layer of smaller sterile cells. The teliospores are red-brown, smooth and round. They germinate to produce a short hypha (promycelium) with 3 to 4 basidiospores (sporidia) near the tip.