The Georgia Agricultural Experiment Station
College of Agricultural and Environmental Sciences
The University of Georgia

2002-2003 Small Grain Performance Tests
Research Report Number 688
July 2003

DISEASES

Barry M. Cunfer and John D. Youmans, Department of Plant Pathology, Griffin Campus, Griffin, GA 30223.

A cool fall and a moderate to cold winter resulted in reduced aphid activity early in the season. This greatly reduced early transmission of barley yellow dwarf virus to small grains. Consequently, barley yellow dwarf caused very little damage. Although only moderate in severity, the largest outbreak of stripe rust ever recorded from Texas to the northern Great Plains occurred in 2003. Stripe rust was widespread in the Southeast but caused little or no economic damage in commercial fields. The disease is usually significant only in the Pacific Northwest. The fungus produces very long narrow pustules with yellow to yellow-orange masses of spores. Stripe rust caused moderate to severe damage in nurseries at Plains, but was found only sporadically in Griffin. The disease is favored by cool temperatures and moist conditions in the spring. Like leaf rust, there are a number of races of the fungus and cultivars vary from highly resistant to very susceptible to stripe rust. A number of sources of resistance are being evaluated in the breeding program. Cold early season temperatures also favored soilborne wheat mosaic virus. Plants are stunted by late winter and have leaves with a yellow mottled appearance. Plants appear to be nitrogen deficient but do not respond to N application. Crop rotation, avoiding early planting, and cultivar resistance are the best management practices for soilborne mosiac.

Powdery mildew was very low this year, occurring only on the most susceptible cultivars. Leaf rust was also relatively low, developing only later in the season due to the cool early season temperatures. Crown rust of oats was low in commercial fields. Several cultivars with excellent resistance are available. Frequent rain favored the most severe damage from Stagonospora nodorum on wheat in recent years. Glume blotch on heads caused lower test weight and yield loss on the most susceptible cultivars. Most cultivars currently recommended have a moderate level of resistance. Several systemic fungicides with excellent activity in controlling foliar fungal diseases of wheat are available. These are Tilt, Quadris, Stratego, and Headline. No evidence of resistance has been found in the U.S. to these fungicides, but varying the fungicide used from one year to the next will help to prevent development of resistance. Cultivar selection continues to be the best management strategy to minimize losses from small grain diseases.

The USDA-APHIS survey again found Georgia to be free of Karnal bunt. The disease has not been found east of northern Texas where an outbreak was detected in 2001. Karnal bunt continues to be a quarantined disease.