Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Soybean Rust in 2008
Last fall, soybean rust was discovered in the Selbyville sentinel plot on the Group VII variety USG7732NRR. 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 Maryland. A sample was collected on October 23 and incubated until October 28. Debbie Parrish examined the sample at the Delaware Dept. of Agriculture 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 PPQ NIS, 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 was no remaining green foliage in this sentinel plot and all commercial fields were in various stages of harvest. 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, either from rust or from unnecessary spraying when the threat of rust is not present.
Asian soybean rust was not detected on soybean or any other host in Delaware in 2008. Leaf samples from sentinel plots in each county were collected over 17 weeks from July 10, 2008 to October 29, 2008. Five to seven sentinel plots were visited each week. Samples consisted of 100 leaves taken from each plot in the lower canopy of plants. Leaves were incubated in plastic bags at room temperature for a minimum of three days, and then the underside of each leaf was examined under low power of a dissecting microscope. Growth stage was recorded as well as foliar diseases and insects present. Data was entered weekly into the ipmPIPE database and the NPDN database.
Current SBR Situation
On March 12, soybean rust was confirmed on kudzu in Miller County, Georgia. On February 27, soybean rust was found on kudzu in Mobile County in the southwest corner of Alabama, however rust could no longer be found on kudzu in Montgomery County. On February 26, soybean rust was found in Cameron County, Texas on volunteer soybeans from a 2008 planting.
Rust activity is pretty slow right now but conditions are more favorable along the Gulf Coast in LA, AL, MS, TX at the present time. It is currently in Mexico as well.
