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In Mid-South cotton: Spider mites busting budgets

Angus Catchot, Extension entomologist for cotton and soybeans at Mississippi State University, has a new nickname for spider mites.

He knows cotton farmers may have names for the pest that can't be printed in a family newspaper.

“This is my term, but, if you grow cotton and you consult on cotton in some of these areas, I think you would agree with this statement wholeheartedly,” Catchot told participants in Cotton Incorporated's Crop Management Seminar in Memphis.

“Spider mites, at least for the South or the Mid-South, are the insecticide budget-busters of cotton production. They are very expensive to treat. When we spray for spider mites, generally it's with a material, either a miticide or an acaricide, that will only control one pest, spider mites.”

The Mississippi Cooperative Extension Service has not budgeted for controlling spider mites in the past because they have been sporadic or occasional pests of cotton, according to Catchot. But that situation is changing.

“In the last couple of years, we have increased the incidental pest column in our Mississippi State cotton budgets to reflect what we're having to do with spider mites,” he said. “Our growers take them very seriously, and certainly our consultants take them very seriously because we've seen what they'll do over the last couple of years.”

Catchot was one of a group of Extension, university, USDA and industry speakers who discussed insect management during the opening session of the Cotton Incorporated Seminar. More than 200 persons attended the event.

Until 2004, he noted, Mississippi cotton farmers rarely treated more than 100,000 acres for spider mites and those mostly in hot, dry years. In 2004, treatments for the pest jumped up over 100,000 acres. In 2005, the figure rose to 275,000 acres and, in 2006, to more than 400,000 acres.

“In 2005, which I've called an unprecedented year, we treated just under 300,000 acres. Then in 2006 we sprayed at least 415,000 acres. You can tell we're having serious problems,” he said.

He said entomologists in Georgia and other states have reported similar outbreaks in recent seasons.

Spider mites traditionally have been considered a “cut out-type” pest in the Mid-South in that they appeared late in the season when growers finished making insecticide applications, Catchot said.

“In fact, they typically occurred so late that growers often were in a quandary as to whether they should treat or not,” he noted. “In Arkansas, Louisiana, Mississippi and other areas now, we're seeing spider mites early, and, when I say early, I'm talking about one-leaf cotton.

“They seem to be even more devastating when they occur on small cotton. As I said, we've treated some acres for spider mites every year, but we weren't seeing the damage we've seen in the last two years.”

Mid-South cotton entomologists believe the following factors may be involved in the increased pressure from spider mites: • Delayed burndown of no-till and minimum-till fields and lack of field border management.

  • Hot and dry conditions.
  • Beneficial insect reduction.
  • Increased use of insecticide seed treatments and fewer applications of Temik.
  • Development of resistance to some insecticides.

“Spider mites overwinter as adult females in fencerows, rocks, weeds and crop debris,” says Catchot. “When you delay burning down the weeds until just before planting, they can move to young cotton.”

Entomologists have known that spider mites seem to be more of a problem in years that are hotter and drier than normal. Scientists have learned that the number of days required for a spider mite egg to develop into an adult is shortened as temperatures increase from 25 days at 60 degrees F to five days at 80 degrees.

The number of mites that a single female can produce in her 30-day life span also increases astronomically as temperatures rise — from 20 mites at 60 degrees F to 13,000 mites at 70 degrees and 13 million mites 80 degrees.

“Just like with aphids, there's also a fungus that helps control mites,” says Catchot. “That fungus doesn't fare as well in hot, dry weather. Researchers have also found that rains can knock mites off plants. When it doesn't rain, you don't get that natural reduction.”

Catchot said many consultants are working with growers to try to avoid the use of hard insecticides in early season and preserve more beneficial insects, which, in tandem with the fungus, can reduce spider mites populations early.

The move toward more seed treatments and fewer in-furrow applications of Temik may also be playing a role in the higher infestations of spider mites.

“Maybe the seed treatments are flaring mites,” says Catchot. “But they're not controlling mites like Temik. I don't think we should stop using seed treatments but be aware of the problem.”

Scientists have not found evidence of insecticide resistance in spider mites in the Mid-South, “but it's been documented that spider mites could be the perfect candidate for developing resistance.”

Entomologists are recommending several practices that could help growers treat fewer acres and not bust their budgets when it comes to insect control, according to Catchot

First and foremost, he said, is “don't create your own problems. Start clean and burn down early,” he notes. “You need three to four weeks of clean ground before you plant. Check field borders and clean them up if you find them.”

A number of insecticides provide good control of spider mites, but consultants and growers need to be aware of the strengths and weaknesses and “best fits” of different products.

“When conditions are favorable for spider mite development and rapid reproduction is taking place, true miticides provide the best efficacy,” he said.

“But bifenthrin (Capture) has a place in the late season window with mixed pest populations.

“Don't delay applications and two applications are often necessary to provide adequate control with some products.”

Watch moving equipment from infested to non-infested fields.

And, finally, increase water volume and avoid low drift tips when making applications for spider mites to improve coverage.

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