Cotton takes a beating

Losses to thrips heavy in Virginia Thrips pressure reached historically high levels on Virginia cotton in 2000, says Ames Herbert, Virginia Tech Extension entomologist.

"In our tests, the average lint increase over the untreated control plots was 422 pounds. That's a lot of money lost if you didn't have thrips protection. These were the heaviest losses we've ever seen from tobacco thrips in Virginia," said Herbert, speaking at the Southeast Cotton Conference in Raleigh.

In some cases, he adds, stand losses of as much as 15 to 20 percent were seen in untreated cotton. During the 2000 crop year, researchers looked at several thrips treatments, he says.

"We looked extensively at Gaucho-treated seed, at eight ounces per hundredweight of seed. We also looked at our standard treatment of Temik, at five pounds in-furrow. That's an excellent treatment, and it offers better control when compared side-by-side with Gaucho-treated seed," says Herbert.

When the Gaucho-treated seed was combined with a broadcast application of Orthene 97 at two and a half ounces, control was increased, he notes. "We also increased that rate to four and six ounces. The thrips pressure was so severe that everything we did gave us better looking cotton.

"We also found that the four-ounce broadcast rate of Orthene gave us about as good control as the 6.4 ounce broadcast rate. But, if you band it in a 12 to 14 inch band, you can drop that rate back to two and a half ounces. A four-ounce band showed some improvement, but the two treatments basically were the same. The object of these tests was to look at how much you need and where you can cut it off.

"If you can band it, you can go with two and a half ounces. If you broadcast or tank-mix with a herbicide, a higher rate will pay for itself," says Herbert.

Many growers complained last year about the lack of thrips control in Virginia cotton fields, he says. "In my opinion, this was due to the fact the control material was broadcast at a rate that was not sufficient. When we increased the broadcast rate to four or six ounces, we got the same level of control as we got with the two and a half ounce banded rate."

Thimet at 3.75 pounds alone performed about the same as Gaucho-treated seed alone, notes Herbert. Temik alone also "pulled a pretty good load," he said, and performed equivalent to other treatments.

Other experiments were conducted where no material was placed in-furrow, he says. The goal was to see how foliar treatments would work alone.

"We don't recommend going strictly with a foliar treatment for thrips control. Temik alone at the standard rate out-performed the foliar treatment alone. We see a yield loss when we broadcast rather than band the material," says the entomologist.

All treatments were applied two times, he says. Once at the first true-leaf or cotyledon stage and a second spray two weeks later.

"We don't recommend this because there was a fair amount of aphid activity in our cotton, and we saw a relationship with fields that had been treated twice for thrips. There appeared to be more thrips in those fields."

Research also looked at tank-mixing Orthene with different herbicides, says Herbert. All treatments but the control received a 6.4-ounce broadcast rate at late cotyledon or whenever there's evidence of the first true leaf.

Roundup Ultra was applied with a second Orthene tank-mix at the four-leaf stage, he says. In addition, a three-way treatment of Roundup, Orthene and Staple was made.

"All of these were equivalent. We saw no yield reductions from any of these tank-mixes. We've heard of injury from Staple, especially with these three-way mixes. But in our experiments, we saw no injury."

Research from this past year has led to several recommendations for controlling thrips, says Herbert, including using an in-furrow seed treatment. Also, growers should begin scouting for thrips damage at the cotyledon stage, he adds.

"Many growers waited last year before applying their foliar treatments for thrips until cotton was at the three to four-leaf stage. But by that time, according to our experiments, it was too late. Thrips are attracted to that little seedling - they're feeding on that growing point.

"The damage is done to cotton in the first three weeks. Look at that first true leaf, and if five to 10 percent of the seedlings are deformed because of thrips damage, go ahead and make a treatment."

A further research finding, he says, is that banding improves thrips control. "But we know that most people won't band their treatments. They'll tank-mix and broadcast in order to get the job done quicker. In our opinion, banding improves control."

Herbert also advises growers to apply enough material to do the job the first time. "Don't skimp on the rates. We'd rather see a few more dollars spent than having to come back a second time."

If a thrips problem is detected, he adds, don't wait for a herbicide tank-mix treatment. "By waiting until it's convenient to make the treatment, you may lose several pounds. Earlier is better than later for thrips control in cotton."

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