Southern Rust in Corn
Corn Disease Information Note 2
Steve Koenning – Plant Pathology Extension Corn Specialist
Southern rust of corn is caused by the fungus Puccinia polysora. The rust is considered to be tropical or subtropical in distribution. It does not overwinter in North Carolina. Spores travel on wind from more tropical regions depending on weather patterns. Typically sweet corn in Florida is sprayed with fungicides for this disease. The optimum conditions for rust development are temperatures from 80 to 90 degrees F and high humidity. Ordinarily, southern rust of corn is of little concern to North Carolina growers because spores arrive so late in the season that little or no impact on yield occurs. On average, southern rust is a problem about one in five years. Yield loss due to southern rust, however, can be severe especially when corn is planted late and environmental conditions favorable for disease development persist in late summer.
The symptoms of southern rust are orange to brown masses of spores (urediospores) that erupt through the upper leaf surface (Figs. 1, and 2). Leaves, stalks, and the husks on ears may be infected. Southern rust typically sporulates profusely on the upper leaf surface and only sparsely on the lower leaf surface. In contrast, common rust (caused by Puccinia sorghi) produces spores on both surfaces, often in streaks.
Resistance to southern rust is controlled by specific genes available in some corn hybrids. Hybrids with high levels of specific resistance to southern rust, however, have lower yield potential than many susceptible hybrids. Some corn hybrids have a more general resistance or tolerance to infection by this fungus. Because corn hybrids change so frequently, it best to consult with seedsmen for information on hybrid resistance to various diseases.
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with a specific problem, contact your local North
Carolina Cooperative Extension Service Office. Outside
North Carolina, look for your state extension service
Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data. All recommendations for pesticide use were legal at the time of publication, but the status of registration and use patterns are subject to change by actions of state and federal regulatory agencies
Published by the North Carolina Cooperative Extension Service Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Last update to information: July 2005
Last checked by author: July 2005
Web page last updated on July 2005