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Western Farmer Stockman

Peanut disease foils farmers, baffles scientists

West Texas peanut farmers have been frustrated and agricultural scientists baffled this summer by a peanut disease that defied identification.

“It is schlerotinia,” says Terry Wheeler, research plant pathologist at the Texas A&M Research and Extension Center in Lubbock. “It does not look like schlerotinia and it does not act like schlerotinia in the field but when I isolate the organism in the lab, it is schelerotinia.”

Farmers, mostly in Gaines County, have been bewildered by the disease for much of the summer and some expressed frustration at a recent field day at the Western Peanut Growers Research Farm near Seminole. The crux of their beef is a delay in identification of the organism.

Peanut specialists on hand at the field day explained that the disease growers found this year resembled another peanut disease organism, botritus. The fungicide of choice for botritus, Topsin-M, cost considerably less than the recommended treatment for schlerotinia, Omega. “We’re talking an $8 per acre expense with Topsin-M on a band, versus $32, banded, for Omega,” says Gaines County farmer Ronnie Wallace. “I understand the farmers’ frustration,” Wheeler says. “They need answers and they’re looking at thousands of dollars in control costs, depending on which disease they have.”

Compounding identification, Topsin-M, which is not labeled for schlerotinia, “stopped the infection,” Wheeler says. “It’s not supposed to, but it did.” Wheeler, a research scientist, was called on to identify the organism so growers could select the proper control strategy. “I had to get samples of known schlerotinia from (Extension plant pathologist) Chip Lee and compare the organisms,” Wheeler said. “When I isolated the samples from Gaines County and compared them with Chip’s samples, the organisms were the same.

Looks deceiving “The samples do not look like schlerotinia but in every sample, isolation showed it to be schlerotinia. Every one.” She says the organism is not difficult to isolate in the laboratory, but it takes time. To conduct the research necessary to compare samples took several weeks, longer than farmers can afford to wait.

But Wheeler could not afford to make a wrong diagnosis and risk error and further problems for farmers. “Some of them had to treat with the more expensive material,” she says.

The process should be quicker with a base to work from. “Now, it’s relatively easy to isolate but I still need seven days to grow the organism,” she said. “We can live with seven days,” Wallace says. “We can’t live with three weeks or a month. We need answers sooner than that.”

Wheeler said several peanut specialists looked at the disease in the field and agreed that it was not schlerotinia. “But using standard isolation techniques, we couldn’t identify the disease as botritus, which is easy to identify in the lab, but not in the field. I could not find botritus.” She said digging out information on botritus also posed problems. “I looked through four decades of literature and found nothing,” she said.

Lab surprises Her lab work, however, assured her that the disease was not botritus. “But it did not look like schlerotinia. She says the disease appears to be airborne and schlerotinia, historically, has not been. “And the chemical that was not supposed to work on it was effective.”

She says the Gaines County farmers apparently have a new strain of the disease. “This is a clear change in a well-studied disease,” she said. “And it is a very aggressive form of schlerotinia. It has been very severe in Gaines County this year.” She says the outbreak runs from around Seminole up to Seagraves, near the Terry County line. She’s also looking at a suspicious sample from Yoakum County. “I’ll spend much of the fall and winter working out a procedure to manage this disease,” Wheeler says. “There is no doubt that it’s a different strain. It’s not your typical schlerotinia so other fungicides might be effective on it. What we have to consider now is how to control it.”

Which is exactly what Wallace hopes for. “I still don’t know what I have in my fields,” he says. “It’s been frustrating that some experts say one thing and others say something else.” He says infection on his farm “is very bad in some places and spotty in others. And I don’t really care what it is; I just want to know how to stop it.”

Wheeler says farmers must be careful not to spread the disease this fall as they finish up and harvest the crop. “The bad thing about schlerotinia is that once it gets started it’s there for the life of the field.”

Wheeler says despite the problems with identification, the solution has depended on cooperation from a lot of people, including farmers, consultants, and Extension and research scientists.


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