On July 24th, soybean rust was found on soybeans in Brooks County, which is located along the Florida line in south central Georgia. The two previous finds in this county, at the University of Georgia’s Attapulgus Research Center, have been on kudzu.
Currently rust has only been found on this year's soybeans in four different counties in three states (Alabama, Florida and Georgia), the rest of the finds have been on kudzu. In Alabama, rust over-wintering on kudzu in central Alabama has not moved to soybeans and has not been found in recent checks on the same kudzu.
With nearly 20 inches below normal rainfall throughout much of south Alabama, rust has not made any significant movement across the state. In Georgia, drought conditions in south central and southwest parts of the state have been severe and rust movement is expected to be delayed.
A total of 25 counties have reported rust this year and include five in Alabama, 12 in Florida, five in Georgia, two in Louisiana, and one in Texas. In South Carolina, John Mueller, a plant pathologist at Clemson University says no spores were reported in traps in mid-July. Though spores were found in a trap at the Edisto Research and Extension Center in Blackville, S.C. earlier, no rust has been found on soybean plants at the research facility in 2006.
So far, no rust has been reported in North Carolina or South Carolina in 2006 on either kudzu or soybeans. In South Carolina, Mueller says, areas which received significant rainfall will probably see downy mildew and possibly frogeye leaf spot developing in soybean fields with full canopies. These should be easily distinguished from rust by your county agent.
“There is no need to spray for downy mildew as it will ‘dry up’ when we hit another dry spell. Frogeye leaf spot is important only on very susceptible cultivars. Spraying for frogeye leaf spot is usually needed only in very wet, late summers and falls on very susceptible cultivars,” according to Mueller.
“We still have not found rust on soybeans or kudzu in South Carolina. The rust in Georgia is a long distance from South Carolina. Last year it took four to six weeks to move from the Attapulgus area in South Georgia to South Carolina. Therefore, we still are not recommending spraying fungicides for rust,” Mueller concludes
Spore trapping continues throughout the U.S. using both active and passive traps. Any positive spore trap information does not imply infection has taken place and plant samples are used exclusively for recording positive rust occurrence. Dry to very dry conditions have prevailed in the spore source regions and movement to new areas has been slow.