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Posted 12 November 2008. PMN Crop News.

Maryland Soybean Rust Update

Maryland Cooperative Extension.

College Park, Maryland (October 31, 2008)--Soybean rust was discovered in a University of Delaware sentinel plot. The location upon review was determined to be just over the border and thus technically in Maryland in Worcester County, between Bishop, MD and Selbyville, DE. This is the first report of soybean rust in either Maryland or Delaware. The sentinel plot was a late-planted Group VII soybean deliberately chosen to provide green susceptible plant material late into the season. A sample was collected on October 23 and incubated until October 28. Debbie Parish of the Delaware Soybean Rust team examined the sample and determined there was a suspect soybean rust infection. Nancy Gregory, University of Delaware Plant Diagnostician and Bob Mulrooney, University of Delaware Plant Pathologist then examined the sample. They determined that there was one soybean rust pustule on one leaf out of the 100 leaf sample. Dr. Mary Palm, USDA-APHIS, confirmed the identification on October 29, 2008.


The primary significance of this find is to illustrate that soybeans in the Mid-Atlantic region can become infected with soybean rust given the right combination of events. However, this particular discovery has no direct implications for soybeans in our region. It happened at the very end of the growing season, and in fact frost (approx. Oct 20) had already damaged the upper most foliage of this extremely late soybean sentinel plot. There is no remaining green foliage in this sentinel plot and all commercial fields are in various stages of harvest. Furthermore, soybean rust is not seed-borne and has no overwintering mechanism other than survival on live host tissue, so the organism cannot establish itself in our region. Any infections that may occur in subsequent years will depend on reintroduction of spores from long distance. The key message to take from this find is that soybean rust can blow into our region and under the right combination of temperature, moisture and plant susceptibility could cause infection in our soybean crop. It will take a combination of unusual events to provide those favorable conditions earlier in a growing season to be a significant threat. Nevertheless, we must keep vigilant to protect this significant component of our agricultural economy.

This detection also illustrates that under the present set of standards, soybean rust can be detected at very low incidence. This ability gives us the information to provide growers an early warning in time to take protective measures in case it should appear earlier in the season when the crop could be at risk. The ipmPIPE program has been a very effective tool for monitoring the presence of soybean rust in the US and preventing this disease from causing needless losses from rust or unnecessary spraying when the threat of rust is not present.

Authors and Contacts:
Arvydas (Arv) Grybauskas

Bob Mulrooney