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Cotton yields reduced by thrips, nematodes

Thrips and nematodes are hard to find, harder to control, and generally work together to create problems for cotton growers. In 2006 the upper North Carolina-southern Virginia Cotton Belt was ‘thrips central’ and combined with nematodes the damage from these two tiny pests will cut into cotton yields from South Carolina to central Virginia.

“Entomologists and plant pathologists have to work together to find ways to manage these pests,” says North Carolina State University Plant Pathologist Steve Koenning.

Temik is a unique pesticide in that at rates used in cotton it provides fair nematode control and good thrips control. It would be a better nematicide, Koenning says, if it weren't so good as an insecticide, he says.

One option for nematode control, Koenning says, is Temik at 5-7 pounds per acre, plus Vydate. This combination has worked well in some areas of the country, but not in others.

In the Delta, growers have seen good results from the combination in about one year out of three. “That level of results makes it tough for us to recommend it in North Carolina,” Koenning explains.

Telone at 3-6 gallons per acre or Vapam are other options for nematode control in cotton. Koenning says research shows that two gallons of Vapam is equivalent in control to one gallon of Telone. Telone costs about $12 per gallon and Vapam cost $4-$5 per gallon.

Vapam may require some specialized equipment for application. Plus, Vapam is tough on metal equipment, so it may require more frequent changing of applicators.

The extra cost of applying Vapam should be a consideration when comparing the total cost of the two soil fumigants for use for nematode control in cotton.

With either Telone or Vapam, growers will need to include an insecticide or plant insecticide treated seed to control thrips. Though these soil-applied fumigants may provide better control of nematodes in cotton, they provide no protection against thrips or any other insects.

In North Carolina, Koenning says, only 10-15 percent of North Carolina cotton fields need treatment for nematodes. The use of Temik is economically attractive for nematodes because a grower gets good thrips control.

Likewise, the soil fumigants are attractive because these materials allow a grower to apply chemicals only to fields where nematodes are a problem.

Newer seed treatments, like Avicta, have been used for nematode control. Nematicide coated seed are convenient. However, using a seed treatment for nematode control takes away the option of spot application.

With only a small percentage of North Carolina cotton fields needing a nematicide, many growers planted nematicide-treated seed on fields that didn't need it.

Avicta only provides nematode activity, so an insecticide treatment, like Cruiser, must be included in the seed treatment.

In addition Avicta provides seed-coated fungicides. Virtually all cotton seed comes with fungicide treatments, and in many cases, the fungicides provided by Avicta duplicate what is already on the cotton seed.

At 40 cents a pound for cotton, it really doesn't matter how nematodes are controlled, as long as they are controlled, Koenning says. If cotton goes up to 60-80 cents a pound, Telone or Vapam may have a bigger role in nematode control.

In 1,100 pound per acre cotton, nematode control is always going to be economically viable. In low yield environments, such as created by drought, with the result being cotton worth $500 per acre, none of the nematicide treatments used will be economically feasible, Koenning says.

Last year, we had nematode control tests in a field that didn't get rain for 55 days, all those treatments showed a loss in profit to the cotton farmer, he explains.

“If you can tell me before you plant your cotton what your yield will be, I can give you a very accurate prediction of how much nematode control you need. That is the major problem with nematode control — it is difficult, bordering on impossible, to know how much control is needed, he adds.

The other half of the destructive tiny duo — thrips appeared in near record numbers across the northern one-third of North Carolina and southeastern Virginia this year. The corridor has been dubbed “thrips central' for good reason, says North Carolina State University Entomologist Jack Bacheler.

Hopefully, everyone who planted cotton in this area either used a seed treatment or Temik. If a seed treatment was used, it should be clear by now that a foliar spray is also needed for full season control, Bacheler says.

The use of Orthene or similar foliar insecticides at the first true leaf stage, or about three weeks after planting, is critical to thrips management, Bacheler says. “We have good research evidence that shows after three weeks, within a few days you might as well not have anything on your cotton plants for thrips,” he warns.

Seed treatments with an insecticide, plus Orthene at quarter of a pound rate, applied at three weeks after planting provided similar results to Temik, the North Carolina researcher contends.

If the seed treatment, plus Orthene system is well-timed, it should be comparable to Temik at 5 pounds per acre, according to Bacheler.

In 2006, heavy populations of western flower thrips were a huge problem in North Carolina and Virginia. These pests require a half to three quarters of a pound of Orthene to control these pests, and even this level of insecticide doesn't always provide adequate control, he stresses.

Cost-wise, if a grower can piggyback Orthene with a glyphosate application, it should cost approximately $3 per acre.

Seed treatment cost will vary, depending on seeding rate. The cost of Temik, compared to the seed treatment, plus Orthene is comparable.

Another factor for growers to consider is the cost of controlling mites, which sporadically occur in combination with thrips.

In a statewide survey of over 150 growers, Bacheler says less than one percent of those using Temik sprayed for spider mites. By comparison, five percent of growers using seed treatment, plus a foliar insecticide, sprayed for spider mites.

In many cases, growers in North Carolina and Virginia had to use a foliar spray behind Temik, because of the extremely high numbers of thrips in 2006.

The combination of Temik and Orthene is probably the No. 1 treatment for thrips in North Carolina, Bacheler concludes.

Managing nematodes prior to planting and thrips in the first month of a cotton crop pays off big-time in the fall. How to most economically manage these pests is an ongoing problem for researchers in the Southeast. So far, it seems the new and the old are comparable in costs and efficacy.

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