The U.S. Department of Agriculture recently released a national pest alert on soybean rust. Although this might not be an issue right now, there are about 6,000 acres of soybeans grown in Butler, Beaver and Allegheny counties each year.

Two fungal species, Phakopsora pachyrhizi and P. Meibomiae, cause soybean rust. They are spread primarily by wind-borne spores that can be transported over long distances.

Asian soybean rust, P. Pachyrhizi, the more aggressive of the two species, was first reported in Japan in 1903 and was confined to the Eastern Hemisphere until its presence was documented in Hawaii in 1994. Currently, distribution of this species also includes Africa, Asia, Australia and South America. Losses from 10 to 80 percent have been reported in Argentina, Brazil, Paraguay, South Africa and Zimbabwe.

The less aggressive rust, P. meibomiae, is present in the Western Hemisphere, including in Puerto Rico.

Neither soybean rust has been detected in the continental United States as of May.

Seed-borne transmission of the disease has not been documented, but there is some concern that seed lots may contain small amounts of infected plant debris capable of spreading the pathogen. To date, however, seed lots have not proven to be a pathway for the disease. The only known ways of spreading the disease are airborne - blown by the wind - and by people. Spores can stick to clothing.

P. pachyrhizi is capable of infecting more than 90 species of legumes.Kudzu, a member of the pea family, is widespread in the U.S. and could serve as a reservoir for the soybean rust pathogen. The broad host range of the fungal pathogen increases the likelihood of rapid spread once introduced into America.

Soybean rust symptoms are similar for the P. pachyrhizi and P. meibomiae species. Symptoms begin on the lower leaves of the plant as small lesions that increase in size and change from gray to tan or reddish brown on the undersides of the leaves. Lesions are most common on leaves, but may occur on petioles, stems and pods.Soybean rust produces two types of lesions, tan and reddish brown. Tan lesions, when mature, consist of small pustules surrounded by slightly discolored necrotic areas with masses of tan spores on the lower leaf surface.Reddish-brown lesions have a larger, reddish-brown necrotic area, with a limited number of pustules and few visible spores on the lower leaf surface. Once pod set begins on soybeans, infection can spread rapidly to the middle and upper leaves of the plant.Environmental conditions impact the incidence and severity of soybean rust. Prolonged leaf wetness combined with temperatures between 59 and 86 degrees and humidity between 75 and 80 percent is required for spore germination and infection. Under these conditions, pustules form within 5 to 10 days and spores are produced within 10 to 21 days.

All commercial varieties of soybeans currently available are highly susceptible. Current research includes screening germplasm for resistance and evaluating fungicide efficacy. Early detection is required for the most effective management of soybean rust.Monitoring soybean fields and adjacent areas is recommended throughout the growing season. Fungicide applications may reduce yield loss, depending on the plant development stage, time when soybean rust is detected and fungicide application method. For efficacy information on fungicides labeled for use on soybean, consult local extension personnel.For more information, you can also go online to www.ncipm.org/soybeanrust.