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Rust widespread in Georgia field; acres of snap beans are nearby
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By Colleen Scherer and Greg Vincent
StopSoybeanRust.com
4/27/2005 – 11:46 p.m. CST (Update with photos) -- The Asian soybean rust found Monday and confirmed today on volunteer soybeans in Seminole County, Georgia, was visible and sporulating on several plants across the field, according to the county agent who found it. And those plants are right next to a large acreage of very young commercial snap beans.
“We found the soybean rust on volunteer soybeans, and suspect it’s on kudzu, as well, in a field that had soybean rust last November,” said Rome (W. Jerome) Ethredge, the University of Georgia Seminole County Extension Coordinator who found the rust.
“The volunteer soybeans are in R1 right now. The rust was widespread on the field and was on many plants. Lesions are visible on the leaves,” he said. “Georgia County Extension agents are monitoring the field and area fields.”
Haley Ethredge, daughter of Seminole County (Georgia) Extension Coordinator Rome Ethredge, poses by the rust-infected volunteer soybeans discovered by her father on Monday, April 25, 2005, near Donalsonville, Ga. Photo by Rome Ethredge.
This is the first confirmation of rust outside of Florida in 2005, and the first to be found on soybeans as the host, vs. kudzu, so far this year.
Ethredge said he found out about the rust when he called a local farmer on the phone and asked him if he had any volunteer soybeans. The farmer said when he was out disking his field, he did see volunteers and that they looked a little “rusty.”
When Ethredge got in the field, he said, “there was a little mottling on the upper leaves and speckling on the lower leaves.”
He said he could not tell if there was a spore buildup in the field, but said the rust is producing urediospores. He also said the area has been known to get Southern corn leaf blight, another plant fungus whose spores travel by air.
Enlarged portion of photo showing rust lesions on volunteer soybean leaves in Seminole County, Ga.
Local farmers in SW Ga. advised to spray beans at R1 stage
Ethredge said he is recommending that local farmers spray a preventive fungicide at the R1 stage.
“Within 20 feet of the field that had rust, there is a large acreage of commercial snap beans that are very young. They may have to put a fungicide on it, but it’s up to the farmer to decide that,” he said. “We will be watching that field particularly close.”
Ethredge said finding rust so soon was a surprise. "We expected to find soybean rust here, but we didn’t expect to find it so early. We expected it to come in later in the season.”
New spore transport forecasts from Georgia source point
The North American Plant Disease Forecast Center started predicting the trajectory of potential spore travel from this new rust site at Donalsonville, Ga., late today.
The first forecast for Wednesday (today) and Thursday is for low threat and low risk to “susceptible plants near the source and along the forecast pathways for Wednesday and Thursday.” It set the threat and risk low because sky conditions are expected to be unfavorable for spores to survive even if they are transported, and no rain is predicted near the source or along the pathways for the two days.
According to the National Weather Service, Bainbridge, Ga., was reporting wind out of the west at 15 mph with gusts to 24 mph with 79 degrees F and 34 percent humidity. Clear weather is expected through the rest of the work week, but the NWS was predicting a 50 percent chance of rain on Saturday. The wind was expected to quiet down Wednesday night to between 5 and 10 mph. A new forecast from the NAPDFC will be issued on Friday.
Southern experts react to new rust discovery
Two states to the west of the new find, in Mississippi, two specialists have been leading efforts to scout for rust in that state. Alan Blaine, Mississippi State Extension agronomist and Billy Moore, Mississippi State Extension plant pathologist emeritus reported that, so far, there are no indications of rust in the areas where they have scouted, even with recent weather being well-suited to disease development.
“The intriguing thing is, we haven’t found anything here in Mississippi,” Blaine said. “After studying the wind currents, I don’t see how we could have a big problem here, but I think we can expect minimal problems.”
Blaine also said the soybeans that are up vary greatly in their growth stages.
“I was in a sentinel plot today that was planted on February 18, and I found blooms today. The soybeans there were in the V4 stage, but I was also in a field about 100 miles to the north that were planted on the same date, and there were no blooms yet,” he said.
Moore confirmed his scouting experience has been similar to that of his colleague Blaine. Moore said he had been scouting fields in southern Mississippi today, where conditions are excellent for spore development, but they have not found anything yet.
“We’ve been looking, and we haven’t found anything,” Moore said.
Despite not finding any rust in Mississippi, weather conditions have been favorable for rust development.
“We have had rain the past several days, and the temperatures have been optimal -- between 59 and 77 degrees Fahrenheit,” Moore said. “We have also had heavy dew at nights on the grass, so I am encouraged by that.
“It’s possible we could have missed it today, though, if there is an extremely sparse pustule development. Spores could develop over a 10-day period. So, if we miss it this week, we could see it next week.”
The MSU team will return to Starkville, Miss., with their scouted samples tomorrow night and should have a better idea on Friday or early next week about whether their predictions that rust is not in Mississippi are correct.
Georgia rust likely to have overwintered, spread locally from host plants
Blaine believes the case found in Georgia was probably from rust that had overwintered in the local area, but he also believes it is a result of sporulation from other host plants.
“I think it sounds like it overwintered, but it had to have a live host. So it could be moving, too. The soybeans weren’t out there all winter, and my best guess is these beans emerged in late January.”
Moore was one of the first scientists in the United States to spot Southern corn leaf blight when it entered the country in the early 1970s. Spores from that disease are similar in nature to Asian soybean rust, and its spread has been studied extensively to estimate how rust may move through the U.S.
However, because of the wind currents that Blaine pointed out, Moore agreed that the rust development in Georgia was a local event rather than likely being spread from Florida.
But with the information from Ethredge that the area where the rust was found this week in Georgia had clear lesions and sporulation is occurring, Moore said Georgia growers should take a more aggressive approach to defending against rust.
“Any time there is spore buildup, there is the possibility for it to move hundreds of miles in one day,” he said. “I’d be looking for it in any soybean field east and north of there.”
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