On Tuesday (July 26), more Asian soybean rust was confirmed in Georgia. The latest discovery was on two leaves in a Colquitt County sentinel plot. Colquitt County, in the state’s coastal plain, is southwest of Tift County, where rust-contaminated leaves were collected on July 15.
“The two infected leaves — out of 100 collected — were gathered on Monday (July 25) out of Group IIIs or IVs,” said Bob Kemerait, Georgia Extension plant pathologist. “Those two leaves had pustules and an abundance of spores.”
Tuesday (July 26) was a busy day for Kemerait. Besides announcing the new rust find, he toured southwest Georgia with Glen Hartman, a University of Illinois plant pathologist.
“Hartman is a rust ‘guru’ working with the USDA. He wanted to determine how widespread rust is in the state. We looked very hard for rust in commercial beans and kudzu and didn’t find anything obvious. That bolstered my opinion that rust isn’t progressing across the state quickly. It’s out there but it’s still very difficult to find, even in plots where it’s been confirmed. It takes a microscope to find. You can’t just walk out in a field and say, ‘There it is.’”
In mid-July, when rust was found in Tift County, growers in the area were told it would be prudent to protect their soybeans with a fungicide. Kemerait still believes that advice is solid, “especially if beans are going into the bloom stage. Protective sprays are probably a good investment anyway. We’ve seen a lot of frogeye.
“However, with the low incidence of rust in southwest Georgia — the most likely spot to see it — it’s understandable if a grower wants to hold off and see what happens. As slow as rust is moving, even if it moves into his area, a grower probably has time to put out a fungicide. Rust is creeping rather than exploding.”
How much spraying has Kemerait seen?
“Many growers have sprayed but there are a lot who haven’t. Those who sprayed typically have a mindset of, ‘I’m going to do this and protect my crop for three weeks and then reassess.’ If a grower isn’t scouting fields closely and doesn’t want to, they should put a protective spray out. If they’re scouting hard, they probably have time to get a curative spray out before rust reaches their fields.”
At season’s start, Kemerait said fears were of, “an explosion of rust. That hasn’t materialized. We were preparing growers for an early, rapidly-developing epidemic.
“We’re scratching our heads about why that hasn’t happened. The most logical explanation is there’s not a critical spore mass out there. Conditions have been favorable and the crop is at the right stage for rust. But speculation is there isn’t a spore mass large enough to cause widespread disease.
“Of course, we don’t know what the next few weeks will bring, but some of our beans are at R-3. Many are at R-2. We don’t have to go that much longer before we’re out of the worry window.”