Transgenics Have Limitations

Growing cotton has become more convenient. Transgenic traits have made that possible, and cotton production is exponentially better because of them.

But total reliance on the transgenic technology does have its limitations. It is becoming more and more apparent that we cannot rely solely on herbicide-tolerant traits. Marestail and pigweed resistance says so. Late-season problems with insects outside the spectrum of Bt control say so, too.

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And believe it or not, late-season insect problems and the presence of resistant weeds are not unrelated. According to the publication “The First 40 Days” – essentially a manual of Best Management Practices (BMP) from the National Cotton Council – spider mite populations can build up in pigweed, and plant bugs can do the same in marestail.

“There’s a lot that goes on in the first 40 days,” says Dr. Bill Robertson, the NCC’s manager, Agronomy, Soils and Physiology. “That can be as much as one-third of the season, and as little as one-quarter of the season. It’s really important that we get off to a good start.”

It’s axiomatic that a cotton crop that gets off to a slow start rarely reaches its full potential. “Getting off on the wrong foot is hard to correct,” says Robertson. “There will always be things that are out of your control, but there are things you can do management-wise to help minimize them.”

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Tried, True

An older product that continues to be effective is Temik insecticide/nematicide from Bayer CropScience.

“Temik has been around since 1970,” says Chris Kleyla, Bayer’s Product Manager – Insecticides. It is effective on mites, piercing and sucking insects, and nematodes. “We start with Temik because we call it the grandmother – she is the one who brought us everything else in cotton.”

“The First 40 Days” notes that residual insecticides can minimize the need for foliar applications outside the Bt control spectrum.

Temik is most commonly used in-furrow at planting, but it can also be used as a sidedress. “That’s one of the great things about Temik – it is flexible; not only in rate, but also the timing of application,” adds Bayer Product Development Manager Lee Hall. “You can sidedress up to the 8th node. This not only allows the grower to have more control of nematodes, but it also has an impact on plant bugs.”

And Speaking of Plant Bugs …

The 2007 season saw one of the worst plant bug years in memory.

“I don’t know if there was anything we could have done to prevent what happened last year,” says Dr. Angus Catchot, Mississippi Cooperative Extension entomologist. “Last year we had some areas that were just overwhelmed.”

Catchot says a group of entomologists in Mississippi, Arkansas, Louisiana and Tennessee is working to come up with other BMPs to help prevent a recurrence of what happened in ’07. “We’re working on things that we can implement, along with chemical control, to try to help farmers reduce sprays. None of them by themselves are completely effective, but as a system incorporated with chemical control, they could be.”

One component of the group’s BMPs is more emphasis on earliness. “We have been looking at some data by Dr. Jeff Gore on the difference in plant bug populations in maturity extremes of varieties.”

Gore is a Mississippi State University research entomologist, and his work involved Deltapine 444 BG/RR, a very early maturing variety, and Deltapine 555 BG/RR, a very late variety.

“Plant bug populations peaked just about the time the 444 matured, which could have saved two sprays,” explains Catchot. “This is just an example of showing what earliness is, and we’ve gotten away from it.”

The “First 40 Days” recommendations also call for the elimination of “convenience applications” of insecticides in tank-mixes with glyphosate if economic thresholds for the target insect have not been met. First, the application is not as effective. Second, convenience applications can flare populations of non-target pests. And third, they can reduce populations of beneficial insects.

Captions (2):

Plant bug damage in cotton next to corn.

Dr. Angus Catchot

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