Flag Smut

Urocystis agropyri

Symptoms: Masses of black teliospores are produced in narrow strips just beneath the epidermis of leaves, leaf sheaths and occasionally the culms. Diseased plants often are stunted, tiller profusely and the spikes may not emerge. A severe infection usually induces the leaves to roll, producing an onion-type leaf appearance. The epidermis of older diseased plants tends to shred, releasing the teliospores (14).

Development: Germinating kernels or very young seedlings are infected by germinating spores on the seed or in the soil. The disease continues to develop systemically, and the black subepidermal strips of teliospores become visible near heading. Infection is favored by low soil moisture and cool soil temperatures.

Hosts/Distribution: Bread wheats are the primary hosts of flag smut fungi, and the isolates attacking bread wheat tend to be so exclusively. There are few reports of flag smut on durum wheats and triticales. The disease is found in most winter wheat areas and in cool, fall-sown spring wheat areas.

Importance: Flag smut generally is not an economically important disease, but where present, yield losses can range from trace amounts to moderate levels (when susceptible cultivars are grown).