By Clint Thompson
Soybean farmers need to be wary of soybean rust disease, which overwintered in Baldwin County, Alabama and Mobile County, Alabama, according to Edward Sikora, professor and Extension plant pathologist in the Department of Entomology and Plant Pathology at Auburn University.
He stresses that the pathogen’s presence in Alabama doesn’t mean there will be an outbreak of the disease this year. However, it does suggest there is potential for an epidemic later in the season.
“It was a mild winter so the kudzu that (rust) survives on, green kudzu, it stayed green in some of these coastal areas and protected areas down south. We’ll see that every couple of years, that’ll happen. Rust is present well before the soybeans are in the ground,” Sikora said. “What we normally see with rust, it will survive on kudzu and can build up a bit on kudzu, but kudzu is not a great host like soybeans. So, the inoculum does not really explode on kudzu as we see when it gets into an unprotected soybean field.”
There are various factors that will affect the disease’s impact this year including rainfall, average daily temperatures and the emergence of early season tropical storms. Sikora said the disease does not fare well in extreme hot temperatures, which was the case a year ago.
“What we saw last year was with the wet weather in the spring, we felt rust could start building up on kudzu so we would have more disease inoculum going into the season. But this disease does not like it hot. It doesn’t like it 95 (degrees) every day and it doesn’t like it hot and dry. Once we started getting into, depending on what part of the Southeast you’re at, late July and August, it really just inhibited the disease from progressing,” Sikora said.
He noted that soybeans are normally planted in May through the middle of June. He added that growers who put out a fungicide application at the R-3, R-4 growth stage should be fine. But if conditions are hot and dry, an application may not be necessary.
Sikora wants growers to be aware of the disease’s presence because of the potential devastation it can do to a soybean crop.
“Once it gets going, it can really do some damage. For example, I had fungicide trials all over the state last year and because of the drought, I saw very little disease pressure,” Sikora said. “But I had one trial over at the E.V. Smith Research Center which is over by Montgomery. We were overhead irrigating weekly in that trial. We planted late in June. We ended up with a 25% yield loss due to rust in that test. We were evaluating three different fungicides in an unsprayed control (plot), and we had a 25% yield loss in the unsprayed control due to rust.”
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