Stripe Rusts of Wheat and Barley

Symptoms include yellow orange pustules oriented linearly between vascular bundles of leaves. Glumes are often infected. Stripe rust symptoms usually appear earlier in the season than other rusts because the fungus develops at lower temperatures than the other rust fungi. As the plants mature, the pustules turn dark and shiny as teliospores are formed. These spores do not play a role in disease development or survival.

Different races (strains) of the stripe rust pathogen affect wheat and barley. The stripe rust fungus has been responsible for some of the most devastating epidemics on wheat in California.

Races that can cause significant damage to barley were confined to Europe until 1975, when they were introduced into South America. Barley stripe rust was first detected in the U.S. in Texas in 1991 and in California in 1993/94. Major epidemics on barley in California occurred in 1996, 1997, and 1998.

The fungus grows only on living host plants and survives between seasons on volunteer wheat, barley plants, and some wild grasses. Rust spores are spread by wind to initiate infections. Disease development is most rapid at temperatures of 50° to 60°F (10° to 16°C) with intermittent rain and dew, although disease can continue to develop at higher temperatures and drier conditions; secondary cycles occur at 7- to 10-day intervals. Races infecting barley can survive in warmer, drier climates. Infections increase water loss and decrease the amount of photosynthate available for grain filling, resulting in reductions in the number and weight of kernels.

Control is achieved through the use of resistant cultivars (see BARLEY and WHEAT CULTIVAR tables). A statewide monitoring program exists for early detection of susceptible genotypes and identification of new resistant genotypes.

In the event that new races of the fungus render current sources of resistance obsolete, foliar fungicides can be applied to control disease outbreaks. Application timing will depend on when initial infections occur and on the specific label restrictions for each fungicide; the objective is to protect the flag leaf from infection and to protect the plant during the grain-fill period.