Though too late to do any damage to the 2006 crop, Asian soybean rust has been detected for the first time in sentinel plots in Kentucky and Illinois.

The late arrival of rust to these states demonstrates the potential for yield loss from the disease.

Rust over-wintered farther north in 2006 than in previous years, but researchers have not yet pin-pointed exactly how far north the disease organisms can survive. Plant pathologists in Kentucky and Illinois stress that none of the soybeans in these states is at risk to rust this year.

The prolonged drought, combined with lengthy record high temperatures and humidity in the lower Southeast no doubt blunted the movement of rust from its typical north to south path.

The arrival of Tropical Storm Ernesto provided needed moisture for the Southeast and seemed to provide a trigger for rust to spread rapidly into the Carolinas and on into the Midwest.

The biggest threat to the country’s highest soybean production areas is most likely to come from rust moving from the Mississippi River Delta, into Arkansas and Tennessee, and on into the Midwest. Though rust was detected early in several parishes in Louisiana and in southeastern Mississippi, weather systems likewise seemed to blunt the movement of the disease from these early detection sites.

While rust will be a major threat to soybeans in 2007, pathologists across the Southeast note that the sentinel plot system worked well in 2006 and gave growers ample time to spray, if needed. In most cases the sentinel plots gave growers the information they needed to NOT spray in 2006, saving them valuable production dollars.

e-mail: rroberson@farmpress.com