August 16, 2006

 

Asian soybean rust found in south-eastern US

 

 

Asian soybean rust has been found infecting a soybean sentinel plot in central Louisiana, prompting local officials to advise that some farmers consider spraying fungicide to protect the commercial crop.

 

The discovery was announced on the US Department of Agriculture's public rust website late Monday (Aug 14).

 

"Asian soybean rust was confirmed on soybeans in Natchitoches Parish, Louisiana on Aug 11," said Louisiana state commentary provided on-site.

 

This is the northernmost confirmation of Asian soybean rust in Louisiana, and the fourth parish to become infected by the plant disease in 2006.

 

State officials recommend that immature soybean fields with good yield potential be sprayed with a fungicide to arrest potential development of the airborne fungus, although they add that most of the Louisiana crop is no longer susceptible to yield damage by the defoliating disease.

 

"Harvesting has begun in many of the soybean growing areas, especially with early maturing varieties or those planted early," they said. "Some late planted beans are in the early reproductive stage."

 

Only 30 US counties have reported rust so far this season--in Alabama, Florida, Georgia, Louisiana, Texas and Mississippi--approximately 100 fewer counties than were found harbouring the disease in 2005.

 

"Extremely dry and hot conditions across much of the south-eastern US have resulted in very limited development of soybean rust this year," said University of Nebraska Extension Plant Pathologist Loren Giesler. "Growers and researchers across the US were on the lookout for soybean rust, but it never developed beyond the south-east."

 

All of the 2006 soybean rust outbreaks have come on kudzu, or in soybean sentinel research plots especially designed to contract the disease, with commercial production thus far remaining untouched.

 

The North American Plant Disease Forecast Centre said Monday that mixed weather conditions will continue to hinder soybean rust development in coming days.

 

"Potential for long-range transport and deposition (of rust spore-seeds) is low," said lead forecaster Thomas Keever, although Keever added that a low to moderate risk of new infections still remains for susceptible plants in Louisiana, Mississippi, Alabama, Georgia and Florida.

 

Asian soybean rust flourishes in temperatures between 17-26 deg Celsius, where dew or rainfall produces high humidity levels, and keeps leaves wet for 6-12 hours.

 

Although the pathogen is a major plant pest in other soybean-growing areas of the world--and most particularly in Brazil--it has thus far failed to cause significant damage to the US crop, since being first discovered in late 2004.