While still not in a gallop across the Southeast, Asian soybean rust moved from a walk to a canter the week of Aug. 21-27.
New soybean rust sites were confirmed Aug. 24 in six Alabama counties: in soybean sentinel plots in Coffee and Henry counties; in commercial soybean fields in Houston, Dale and Pike counties; and on kudzu in Conecuh and Pike counties. Conecuh County is in south-central Alabama with all the other listed counties in the southeast.
“Infected beans in the sentinel plots and fields were at R-3 to R-6,” said Ed Sikora, Alabama Extension plant pathologist. “Generally, the infection level seems low. However, I'm only walking a small percentage of the commercial fields…I believe incidence is low to very low, but I easily could be missing hot spots within fields.”
In Georgia, rust continued its dogged northward trek.
On Aug. 22, soybean rust was confirmed for the first time in a commercial soybean field in Appling County at R-3/R-4. A day later, rust was found in sentinel plots at the Rural Development Center in Tifton, Ga.
On Aug. 24, new cases of soybean rust were confirmed in two research farm sentinel plots in Grady and Oconee counties. The Oconee County site, near Athens, Ga., is the farthest north that soybean rust has been found in the state.
On Aug. 26, a Putnam County sentinel plot — near Eatonton, Ga. — was the next rust site confirmed. Pustules were found on 82 percent of the leaves collected from the plot's Group 2, 3 and 4 plants. On the plot's Group 7 R-3 plants, 19 percent of the collected leaves were infected.
“The biggest surprise we've had is the way rust has progressed,” said Bob Kemerait, Georgia Extension plant pathologist. “It seems to be traveling around 60 to 70 miles per week. Once it got going, we were prepared for rust to be devastating. It hasn't acted like that. It has spread across the state but hasn't destroyed any fields.”
Both Sikora and Kemerait suspect the disease is more widespread than the sites found.
“It has to be in a lot more commercial fields than we know,” said Kemerait. “The rust spread has been so slow a lot of producers don't even know it's there.
“My feeling is we're having little amounts of spores come in to start infection. That's opposed to an overwhelming amount of spores moving in and infecting everything at once. In Brazil, huge spore showers lead to rapid rust infections. Here, that isn't happening.
“I'll go so far as to say this: if we didn't have sentinel plots and weren't looking really hard for rust, I wouldn't have guessed it was in the state.”