New cases of Asian soybean rust have been confirmed in east-central Alabama and southern Georgia. In both cases, plant pathologists say the disease appears to be picking up the pace.
In Georgia — where recent wet, humid weather has been conducive for the disease — rust was again found in Tift County on the Coastal Plain. This time, rust was found on a research field of Group VIIs that have begun dropping leaves.
“Development of the disease in Georgia hasn’t spread over a huge area, but conditions have been right for it lately,” said Bob Kemerait, Georgia Extension plant pathologist. “We’re seeing rust respond more quickly than it has been.”
Ponder Farm, where the latest infected plot is located, is about seven miles from the Lang Farm in Tifton where rust was found in mid-July. Both farms are part of the Coastal Plain Experiment Station.
“The disease focus is in one of my research plots for fungicide control of soybean rust. So if it was to be anywhere, it’s in a spot we want it to be.
“The rust has entered a corner of the plot and is causing defoliation in a limited area. But it seems to be spreading from there. The plants most heavily involved are infected from the plant top to the bottom.”
How significant is infection throughout the field?
“We sprayed an insecticide yesterday so we couldn’t get back into the field. We’re going to go back and check more closely. Right now, though, heavy infection on plants is probably on less than one percent of the field. But there’s certainly more infected. We just haven’t seen symptoms yet.”
The field was first sprayed with fungicides right before Hurricane Dennis landed and again on July 27.
“Not everything in the field was sprayed,” said Kemerait. “No one should make the mistake of thinking the fungicides aren’t working. What we’re hoping to find are bands of green, healthy leaves. Hopefully, the plot shows the efficacy of a good fungicide and the importance of timing and proper application.”
Is Kemerait expecting more cases of rust to pop up in Georgia?
“Absolutely. It’s conjecture, but with the weather we’ve had I expect it will be found in commercial fields very soon. The growth stage we’re at and the widening distribution of the rust leads me to believe that. I feel comfortable with that prediction.”
In Alabama, the latest rust incidence was found in Elmore County. The site is a research station sentinel plot halfway between Montgomery and Auburn. From Auburn, where rust was confirmed on Monday (Aug. 1), the latest site is about 30 miles due west.
The Alabama plot is made up of Group IVs at around R-4/R-5.
“My colleague, Arsenio Gutierrez, found it,” said Ed Sikora, Alabama Extension plant pathologist on Wednesday evening. “He’s really good at locating rust. He’s the one who found three infected leaves on a single plant at the Auburn University plot.”
Sikora said what’s interesting about the latest find is the Elmore County plot is around 30 percent infected. “So from three leaves on a single plant last week, we’re now at about one-in-three plants in this plot showing symptoms. It seems to be moving quicker.”
However, soybeans in surrounding areas still appear unaffected.
“Just today I went up to a Clanton-area sentinel plot in the R-5 stage. The beans were clean. And over the last two days, scouts have also looked at two other plots within about 30 miles of the Elmore County site. Samples from them were all negative.”