April 11, 2008

 

Asian rust poses greatest threat to US soy fields

 

 

Asian soy rust is feared to strike the US agriculture in 2008, as the disease becomes more firmly established, at a time when US farmers plan to increase soy seedings by 18 percent.

 

The fast-moving, windborne fungus (Phakopsora pachyrhizi) is already a major soy pest in Asia, Africa and South America.

 

It was first found on the continental US in Louisiana in November 2004. Since then, the plant disease has moved deeper and deeper into the US interior with each successive year; invading nine states in 2005, 15 states in 2006, and a record 336 counties across 19 states during 2007.

 

University of Kentucky plant pathologist Don Hershman said the rust seems to be moving north, earlier and earlier, every year.

 

Hershman explained that part of it is because kudzu is becoming more uniformly infected. They also find that long-distance spore movement is very common, the scary part.

 

Infected soy plants can produce as many as 4 trillion active rust spores per acre, thriving in cloudy conditions, at temperatures between 59-85 Fahrenheit, and relative humidities of 75-80 percent. Live spores can travel hundreds of miles in just one windy day.

 

Research conducted by Syngenta Crop Protection, Inc. (SYT), a major fungicide manufacturer, indicates that the incidence of rust within an infected field can spread from 5 percent to 70 percent of all plants, in just seven days.

 

Syngenta technical fungicide specialist Eric Tedford said this translates into a potential soy yield loss of 15-30 bushels per acre.

 

Dallas County in Iowa, located in the very middle of the US soy belt, represents the furthest point north that soy rust has been found to date in North America.

 

Although the fact that rust needs living plant tissue to survive, primarily on kudzu weed, which is endemic to the Deep South, also means that the fungus must start over from frost-free areas and resume its northward migration each season, some experts still fear the nasty pathogen may move even further in 2008.

 

Iowa State University plant pathologist Daren Mueller said the arrival of spring has produced several rust-worthy developments.

 

Missouri-based meteorologist Al Peterlin said prevailing weather patterns currently appear to be very rust-friendly.

 

However, an April 3 report provided by the USDA's public soy rust website said the disease does not appear to be on the move, at least not so far, this spring.