January 19, 2006

 

First Asian soybean rust of US in 2006 reported in Alabama

 

 

Asian soybean rust made a quick comeback in 2006, having already been found as far north as central Alabama, as well as across most of Florida.

 

Plant pathologist Ed Sikora of Auburn University reported the nation's first Phakopsora pachyrhizi infection to the official soybean rust website of the US Department of Agriculture.

 

"Soybean rust was detected on two kudzu patches in the city of Montgomery on January 12," Sikora said. "Most of the two patches were dormant, but the remaining green foliage was infected with the disease."

 

Although soybean rust has been found in 34 counties of Alabama since Jun 2005, this was the first finding of the plant disease in Montgomery County. Montgomery, Alabama is situated approximately 125 miles north of the Florida Gulf Coast.

 

The USDA said intensive field scouting undertaken in Florida January 11-13 also resulted in discoveries of the airborne fungus on kudzu in nine Florida counties: Alachua, Duval, Gadsden, Hernando, Hillsborough, Lee, Leon, Pasco and Polk. All counties, except Polk, had harboured rust in 2005.

 

"Some of the sites had significant dieback, due to obvious frost damage in the north and/or natural decline in central and southern Florida," said University of Florida plant pathologist James Marois. "A few sites in the south had no appreciable dieback."

 

Frost-induced kudzu dieback marks the demarcation line for seasonal southward defoliation of this alternative soybean rust host, which is utilised by the disease as a major overwintering refuge.

 

The USDA says winter cold snaps have cause "nearly 100 percent dieback," of the broadleaf vine across all but coastal areas of Texas and Louisiana, plus most of Alabama and Georgia, as well as all of North and South Carolina. 100 percent dieback also extends as far south in Florida as Cedar Key and Daytona Beach.

 

"The kudzu patch in Liberty County (Texas) that had soybean rust in November 2005, has completely died back," reports Texas A&M plant pathologist Tom Isakeit, who said the patch was struck by frost Jan 7.

 

This particular south-eastern Texas kudzu patch--which represented the westernmost discovery of rust in 2005--had been of special interest to rust experts, who estimate that the chance of early disease infections from Texas and western Louisiana eventually spreading to core soybean-growing areas of the Midwest, are about 4 times higher than from more easterly sites, due to prevailing winds off the Gulf coast.

 

A USDA study on the subject suggests that all areas of the US where soybeans are grown stand at least a 50 percent chance of contracting the disease rust annually, with that risk rising to about 70-100 percent for fields lying east of the Mississippi River.