Rusts

Symptoms

Leaf Rust

University of Kentucky Dept. Plant Pathology

Rust can occur April through June. The first evidence of a rust infection are pin-point yellow flecks on the upper side of leaves. The yellow flecks will deteriorate and turn to orange pustules.

Reddish-brown rust pustules usually develop first on the upper side of lower leaves or stems. Epidemics are most detrimental before or during flowering. There is a reduction in plant vigor, seed filling, and root growth in infected plants. Also, rust infections may predispose the plant to other diseases such as powdery mildew.

Causative Agent

Leaf rust fungus can overwinter in Kentucky on fall seeded wheat but most often it is blown into Kentucky from southern states. Warm temperatures and high humidity or rain favor rust development. Leaf rust is a potentially explosive disease; it requires a very short time to go from low to epidemic levels on a susceptible variety. Leaf rust can severely reduce yields if significant disease develops PRIOR TO the soft dough stage of grain development. After soft dough, rust will have little effect on crop yields. Rust is present almost every year in some part of Kentucky, however most years it develops too late to cause extensive damage.

IPM Techniques

IPM recommendations include:

• Planting a resistant or moderately resistant wheat variety
• Allowing air circulation and light penetration into the crop canopy by avoiding planting extremely dense stands
• Planting early maturing cultivars
• Destroying alternate hosts of the rust if the host is known.

References and Additional Information

• IPM-4 Kentucky IPM Manual for Small Grains
• PPA-10c Kentucky Plan Disease Management Guide for Small Grains by D.E. Hershman and Paul Vincelli
• Annual Kentucky Small Grain Variety Trials, Progress Report 355
• PPA-25 Leaf Rust of Wheat
• PPA-36 Fungicides to Control Leaf Diseases in High Yield Wheat
• Selecting Wheat Varieties, Grain Gleanings, Vol. 1, No. 9 (1993)
• Common Diseases of Small Grain Cereals. F. J. International Maize and Wheat Improvement Center, Londres 40, Apdo. Postal 6-641, Mexico, D.F., Mexico
• Compendium of Wheat Diseases, M.V. Wiese, The American Phytopathological Society Press, 1987.

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