August 20, 2009

Arrival of the first Atlantic-spawned tropical storm of the season has heightened fear that Asian soybean rust - now spreading rapidly in the Delta - may soon invade core soy-growing areas of the Midwest as well.

 

Tropical Storm Claudette made landfall in the Florida Panhandle Monday and has produced several days of rain, high humidity and overcast skies throughout the Deep South.

 

The latest infection forecast issued by the US Department of Agriculture warned, "moderate to strong winds associated with Claudette will facilitate spore transport northward from the Gulf Coast into the central Mississippi River Valley. The storm will also be responsible for deposition across the southeast and north into central Missouri."

 

While sunshine kills airborne rust spores, which act as seeds for the disease, rainy weather actively enhances spore survival.

 

"Rust survey coordinators went on "high alert" during recent rains," said Allen Wrather, University of Missouri Extension plant pathologist.

 

Five years ago, the first soybean rust ever found in Missouri appeared in the state's Bootheel, after remnants of a hurricane carried spores inland from the Gulf of Mexico. Soy rust has since been found in Missouri during four of the last five years - but always in late September or October - when beans were almost fully mature and therefore safe from yield loss.

 

But wet weather in Missouri this spring delayed planting, creating a much more dangerous rust scenario.

 

"Soy maturity and harvest will be later than normal," Wrather said. "Rust that develops in September might damage late-maturing soy plants and reduce yield."

 

The USDA last week predicted that Missouri would rank as the nation's seventh-largest soy-growing state in 2009, harvesting 214 million bushels of beans, which would represent 6.7 percent of the nation's 3.2 billion bushel crop.

 

The pathogen prematurely defoliates soy plants, leading to potential yield losses of up to 90 percent, unless quickly countered with chemical fungicide.

 

Soy rust was reported in commercial soy fields of two additional Louisiana parishes Wednesday and has appeared in Arkansas, plus 10 counties of Mississippi during the past week alone.

 

"Recent soy rust finds in Arkansas and Mississippi indicate that soy rust is beginning to move northward from the most southern states," said University of Illinois plant pathologist Carl Bradley. "The northward progression of soy rust along the Mississippi River Valley in the next few weeks will be important for Illinois growers to monitor."

 

In all, soy rust has been found in seven states and 58 counties in the US in 2009, largely along the Gulf Coast from Texas to Florida.

 

"Conditions over the past few days have been quite favourable for the development and spread of Asian soybean rust," said University of Georgia Plant pathologist Bob Kemerait. "The recent tropical storm, even though we were not directly in its path, may have helped to move more spores into our production region and has certainly extended environmental conditions (cooler, wetter weather, plus some wind) that are perfect for development of rust."