Plant pathologist updates growers: West Texans need different handling of peanut diseases

Peanut diseases may behave differently in West Texas than they do in other parts of the peanut belt.

It's partly the semi-arid nature of the region, says Texas A&M Extension plant pathologist Chip Lee.

“For instance, controlling leaf spot makes a difference in yield some years and in some years it doesn't. In 2003 and 2004, if growers above the Caprock applied leafspot controls, they wasted their money. Further south, around Stephenville, that's not the case. Foliar diseases can cause significant yield losses.”

He says just off the Caprock, in the Southeastern part of the Panhandle, growers saw a significant amount of leafspot in 2003 and then did not see it in 2004.

“Above the Caprock we just don't get the moisture. In dry years, we get some leaf scorch, usually in August and September and especially on high pH soils. Pepper leaf spot, with small specks, may show up in a dry year and result in a scorching effect. Leafspot fungicides are of benefit when this happens.”

Lee discussed several disease problems with growers at an early spring production seminar in Brownfield.

He says growers may see more leafspot on Spanish and Valencia peanuts than they will on runner types.

West Texas growers may need to pay closer attention to soil-borne diseases. Several pathogens may infect peanuts from seedling stage through maturity. Lee says farmers who plant peanuts behind a hailed-out or otherwise abandoned cotton field, where they apply a heavier rate of herbicide than is recommended for peanuts, should consider additional seed treatment. “They also might consider a fungicide in the furrow,” he says.

Lee says nematodes have not been a severe problem for West Texas peanuts yet, but a rootknot species does infect the crop in Central Texas and may cause significant yield loss. Cold winters seem to keep the nematode in check in West Texas. “Look for root lesions.”

Southern blight

Lee says Southern blight can cause significant damage to peanuts, “if growers do not rotate. The best schedule is peanuts only one out of four years in a field. Closer intervals can cause problems.”

He says Southern blight grows on dead tissue in the spring and creates an acid that kills live tissue.

No-till peanuts may be a concern for some growers, Lee says, but only if they change tactics mid-season. It's best to stay with the no-till system once it's begun.

“Stay with no-till and leave that residue in the row middles,” he says. “Growers who decide to cultivate in-season after starting out with no-till, may damage peanuts. The worst thing a grower can do is throw dirt onto a peanut plant crown. Plowing at 9 or 10 miles per hour, even with a small shank, can throw dirt onto the plant. Organic matter comes with the dirt and provides an ideal disease situation,” he says.

Covering the plant also delays maturity.

Lee says growers should be aware of two potentially damaging diseases that may create some identity confusion. Sclerotinia and Botrytis may show similar symptoms in the field but specialists recommend different treatments. Botrytis, for instance, succumbs readily to Topsin- M, a relatively inexpensive fungicide. Sclerotinia requires a more costly material.

Lee says Sclerotinia spreads slowly; Botrytis spreads rapidly.

Hard to identify

“It's sometimes hard to determine in the field which disease is present,” Lee says. “If we think it's Botrytis, we treat with Topsin-M. And we want to treat it quickly.”

He says materials recommended for Sclerotinia also control Botrytis, but are expensive.

“We hope that neither Sclerotinia nor Botrytis shows up in 2005. The pattern has been that Botrytis does not appear in consecutive years while Sclerotinia shows up every year.”

He says research is ongoing to develop a better way to identify Sclerotinia and Botrytis and to improve control strategy.

e-mail: [email protected]

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