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Fungicides work primarily as a preventive, says Alan Henn, Mississippi State University Extension professor of entomology and plant pathology, who spoke at the annual meeting of the Mississippi Peanut Growers Association. “Once you have a disease, it’s a lot harder to manage than if you head it off with a proper application of fungicide.”
ALAN ORTLOFF, from left, president of the Clint Williams Company, Madill, Okla.; Marshall Lamb, director of the USDA/ARS National Peanut Research Laboratory, Dawson, Ga.; and Lee Talbot, Brooks Peanut Company, Samson, Ala., were among those attending the annual meeting of the Mississippi Peanut Growers Association.
Monitor storm fronts closely
“Watch these southern storm fronts closely, particularly since NOAA is predicting increased rainfall in August and September. I’d suggest planning for a couple of preventive applications before a storm comes in so peanut leaves are protected if rain-borne spores fall on your peanut crop.
“I’m not suggesting anything fancy — just straight tebuconazole plus Echo or Bravo. Remember, Bravo is just like a raincoat — it protects the part of the plant it covers. And just like a little kid outgrowing his raincoat, as plants continue to grow more area is exposed. The tebuconazole adds a little extra protection in case you can’t get into the fields right away after the rain. I’d suggest a final preventive chlorothalonilapplication. The cost for these applications is about $41 per acre.”
He says he hasn’t seen as much of a problem from Rhizoctonia in Mississippi as expected, “but I have seen significant problems with southern stem rot/southern blight in most peanut production areas. This is one reason you need to choose your fields carefully, to reduce potential for disease before you even plant. Fungicide use to control this disease can boost yield as much as 10 percent.”
White mold rots the plant, cutting off its water uptake, he says. “It attacks the nuts and reduces quality as well as yield. It also produces resting sclerotial structures, which can last in the soil for three years — which is why you need to have long rotations. This disease seems to occur early season on plants in warmer than normal weather.”
Growers should stay away from fields with a history of southern stem rot/southern blight, Henn says, and if it’s necessary to plant in a field with southern stem rot history, “consider an early fungicide application somewhere around 15 days after planting, or a bit later. This will increase your fungicide budget. And if you are planting in such a field this year, I’d like to work with you on small plot studies for early application of fungicides to head off this disease.”
For the conventional seven-application fungicide system, Henn says, cost per acre could range from $130 to $160, based on use of a 350-450 gallon self-propelled sprayer with a 60-foot boom, costing about $103,000, and current fungicide prices and label rate.
“This is based on the assumption that there’s not a lot of disease pressure, that we make all applications as cheaply as possible, that for the first, second, fourth, and seventh application we use a tank mix of generic tebuconazole and a chlorothalonilmaterial such as Bravo or Echo, and a seventh application of chlorothalonil alone.”