WASHINGTON, Nov. 10, 2004 -- The U.S. Department of Agriculture's Animaland Plant Health Inspection Service today confirmed the presence ofsoybean rust on soybean leaf samples taken from two plots associated witha Louisiana State University research farm Saturday.
While this is the first instance of soybean rust to be found in the UnitedStates, the detection comes at a time when most soybeans have beenharvested across the country. As a result of the harvest, the impact ofthe fungus should be minimal this year.
Soybean rust is caused by either of two fungal species, Phakopsorapachyrhizi, also known as the Asian species, and Phakopsora meibomiae, theNew World species. The Asian species, the one found in Louisiana, is themore aggressive of the two species, causing more damage to soybean plants.
USDA will dispatch its soybean rust detection assessment team, composed ofscientific experts and regulatory officials, to the site within 24 hours.The assessment team will work closely with Louisiana State Department ofAgriculture representatives to assess the situation and conductsurveillance around the detection site to determine the extent of thedisease spread.
Soybean rust is spread primarily by wind-borne spores capable of beingtransported over long distances. At this point in time, based onpredictive models, APHIS believes that the detection in the U.S. isrelated to this year's very active hurricane season. While the harvest forthis year is complete, during next year's planting season, producers willneed to watch for symptoms of the fungus such as small lesions on thelower leaves of the infected plant that increase in size and change fromgray to tan or reddish brown on the undersides of the leaves. USDA and thesoybean industry have been cooperating on awareness efforts and willamplify those efforts now that the disease has been found in this country.Lesions are most common on leaves but may occur on petioles, stems, andpods. Soybean rust produces two types of lesions, tan and reddish brown.Tan lesions, when mature, consist of small pustules surrounded by slightlydiscolored necrotic area with masses of tan spores on the lower leafsurface. Reddish brown lesions have a larger reddish brown necrotic area, with a limitednumber of pustules and few visible spores on the lower leaf surface. Oncepod set begins on soybean, infection can spread rapidly to the middle andupper leaves of the plant.
Soybean rust can be managed with the judicious use of fungicides. However,early detection is required for the most effective management of soybeanrust. Monitoring soybean fields and adjacent areas is recommendedthroughout the growing season.
Fungicide applications can reduce yield loss, depending on the plantdevelopmental stage, time when soybean rust is detected, and fungicideapplication method. Efficacy information for producers on fungicides isavailable through state university extension services.