April 17, 2007

 

Easter freeze could chill development of Asian soybean rust in US

 

 

Record cold that struck the US this Easter could ultimately wind up benefiting US soybean growers by reducing the threat posed by the Asian soybean rust fungus.

 

The cold weather likely killed the fungus in parts of the south-east, according to plant pathologists.

 

"We had a record-breaking frost Easter morning, with temperatures in the panhandle below freezing for several hours," University of Florida plant pathologist James Marois told the US Department of Agriculture last week.

 

National soybean rust commentary provided by the USDA said although the exact impact of the frost on rapidly growing kudzu--the primary over-wintering host for the devastating plant disease--is still not fully known, the agency theorised that "it could reduce the build up and potential spread of soybean rust for several weeks".

 

"Prior to this frost event, warmer temperatures had increased the growth of kudzu throughout the south-east."

 

A South Carolina state rust report provided to USDA's soybean rust website said, "kudzu was roughly 75 percent sprouted and growing rapidly when a hard freeze (25 degrees Fahrenheit) across the state on the night of April 7 killed more than 50 percent of the leaves."

 

Drought has also affected the growth, health and spread of kudzu across the south-east this spring, limiting active soybean rust infections to five counties of Florida and three counties in extreme southern Georgia.

 

"In some counties, the infected kudzu has been destroyed and rust in some of those locations is no longer found," said the USDA. "The disease was also detected on soybeans in one county in Texas, but that field has since been cultivated and planted with corn."

 

While the airborne fungus failed to cause appreciable damage to the US soybean crop in 2006, it still managed to move farther north than ever before, eventually appearing in Indiana fields located within about 100 miles of Chicago.

 

In all, soybean rust was confirmed in 274 counties across 15 US states, which was approximately double the number of rust infections found in 2005.

 

The pathogen--which is considered one of the world's worst plant diseases--has the potential to cause severe yield losses through premature defoliation of infected plants unless almost immediately countered with chemical fungicide.

 

While endemic to almost all other soybean-producing areas of the Earth--and a major crop pest in Brazil--the airborne fungus only first appeared in the continental US in November of 2004, likely carried into Louisiana on hurricane winds from rust-infected fields in South America.