Soybean Rust Update for August 15, 2016
from Jim Dunphy, Crop Science Extension Specialist (Soybeans)
and Lindsey Thiessen, Extension Plant Pathologist
So far this month, Asiatic Soybean Rust has been confirmed on soybeans in Baldwin, Dallas, Macon, and Elmore counties in Alabama, in Calhoun County, Florida, in Decatur County, Georgia, and in Choctaw County, Mississippi. This is the first find of rust on soybeans in Mississippi this year. All but the find in Mississippi were in sentinel plots established to detect rust early if it developed. The Elmore and Macon counties finds are 210 miles from Murphy, and 340 & 345 miles from Charlotte, NC. The closest confirmed rust to Charlotte remains Tift County, Ga, which is 305 miles away. All other confirmed finds of rust on soybeans are more than 300 miles from any soybeans north or east of Charlotte.
We still consider our earlier recommendation to not spray soybeans that have not started blooming, or blooming soybeans that are more than 100 miles from confirmed presence of rust on soybeans to be a valid recommendation for most soybeans in NC. We do not recommend spraying for rust after stage R6 (full-sized beans in the top four nodes), since soybeans this mature will probably drop their leaves naturally before rust will cause many to drop prematurely. Check the label on the fungicide you prefer to use to see how late in the season that chemical may be sprayed.
The current status of rust in the continental US can be found anytime at http://sbr.ipmpipe.org.