March 24, 2005

Threat of soy rust movement in US seen moderating

The threat of Asian soy rust being transported to fresh areas of the US has moderated, according to revised forecasts issued late Wednesday by the North American Plant Disease Forecast Center at North Carolina State University.

Although scattered showers, warm temperatures and overcast skies produced good conditions for the survival of fungal spores in already infected areas of the west-central Florida Peninsula Wednesday, the agency added that the threat of disease spread will be ameliorated by offshore winds, predicting "any rust spores that become airborne will move fairly quickly to the northeast and off the coast by evening."

The Plant Disease Forecast Center forecasts a "moderate to weakly moderate risk," estimated at 20-60 percent, of rust infection among susceptible plants in central, east-central and northeastern Florida through Friday, with "low risk," (0-20 percent) expected elsewhere.

The Southern Plant Diagnostic Network at the University of Florida confirmed the discovery of Asian soybean rust (Phakopsora pachyrhizi) in a second Florida county (Hernando) earlier this week, directly adjacent to the only other area (Pasco County) of the US known to be infected by the destructive fungus so far in 2005.

The disease was found in eight southeastern states in 2004.

The disease was once again discovered over wintering on kudzu, a hardy ditch weed found throughout the southeastern quadrant of the US - annually one of the first plants in the nation to awake from winter dormancy.

"Spread of disease into more northerly areas is currently inhibited by lack of green host tissue," said the US Department of Agriculture.

Asian soy rust - found for the first time ever in the US last fall - can reduce soy yields by as much as 80 percent, by defoliating plants, reducing pod set and decreasing soybean test weight.

None of the estimated 16,000 varieties of soybeans currently grown in North America have been found to have any natural resistance to the disease. Although soybeans are its preferred host, Asian soy rust can thrive on nearly 100 other types of vegetation as well.