Impact
Two different rust diseases, leaf rust and barley stripe rust, occur occasionally in the San Luis Valley. Each rust is caused by a different species of the fungus Puccinia. Each type of grain is infected by a separate species. Barley stripe rust occurs only in barley. Leaf rust infects both wheat and barley.
Wind disperses the spores. These fungi do not overwinter in the San Luis Valley. New infections depend on wind introduction each year. Rusts increase respiration and transpiration and decrease photosynthesis resulting in severe plant stress.
Light infections of rust occur throughout the San Luis Valley. Serious problems are rare.

Description and Symptoms

Both rusts are spread by wind-borne spores.

Leaf rust appears as small, round, light orange-brown pustules scattered on leaf sheaths and blades.

Leaf rust head infections are especially damaging.

Stripe rust appears in barley as yellow pustules arranged as stripes on leaves, stem, and heads.

Stripe rust may be very damaging if grain is infected early. Historically,
infections occur only late in the season on late-planted barley.

Integrated Management

Plant resistant varieties to provide a defense against certain races of rust.

Use appropriate systemic seed treatments if early season infections occur regularly.

Avoid late planting (after May 15) to minimize rusts. Timely planting is especially effective to minimize barley stripe rust.

Apply fungicides only in severe epidemics to protect the flag leaf.

This material is based on work supported by the San Luis Valley Water Quality Demonstration Project Best Management Practices Advisory Committee, Colorado State University Cooperative Extension, Farm Service Agency, Natural Resources Conservation Service, and the U.S. Department of Agriculture under authorization as 1991 U.S. Department of Agriculture Water Quality Demonstration Project.