June 1, 2007
Large numbers of thrips are moving from Mid-South wheat into cotton and soybeans. Add in early populations of spider mites and entomologists admit concern.
“Thrips are really driving our worries,” says Gus Lorenz, Arkansas Extension entomologist. “We're in the middle of one of the worst thrips infestations in a long time. They're pouring out of wheat and wild hosts.
“At field edges, growers are burning down weeds with glyphosate and the thrips are jumping into cotton and soybeans. The thrips population is through the roof.”
Louisiana has “a lot” of wheat acreage this year, says Ralph Bagwell, LSU AgCenter entomologist.
“And much of the wheat is around cotton fields. Thrips have moved and caused fairly high amounts of damage to the cotton.”
Some regions of the Mississippi Delta are seeing “extremely heavy thrips pressure requiring foliar applications,” says Angus Catchot, Mississippi Extension entomologist. “And those are coming behind seed treatments and Temik.
That isn't to say the seed treatments and Temik aren't doing their jobs. This is a numbers game — in some areas there are so many thrips it's hard to keep them in check.”
Lorenz has fielded many calls claiming seed treatments and in-furrow insecticides aren't working. He doesn't believe that's the case.
“I think they're simply being overwhelmed by thrips. I've heard from folks claiming, at cotyledon stage, 100 thrips per plant.”
And the spider mites are lurking.
“Our concern is two-fold,” says Catchot. “Getting the thrips under control is job number one.
“Just behind that are concerns about flaring the secondary pests. If the weather turns off dry and we make a lot of broad spectrum insecticide applications to knock thrips back, the mite situation can become much worse.
“We know acephate and pyrethroids can be very bad for flaring mites. But in situations where the thrips are knocking terminals out, we have to treat.”
In such situations, Catchot and colleagues recommend Bidrin or dimetholate.
“Nothing is great to keep from flaring mites but those two products are much less likely to.
“Really what we're trying to do in traditional spider mite areas is hold off treating for thrips unless we absolutely have to. It's been cool and the plants have been held back. With a bit warmer weather, we're hoping the plants can grow and reach a stage where the thrips are less of a bother.”
“Another concern is the perception that we can make one application for spider mites and be done. This often is the case late-season where plants have slowed growth and we use some of the newer miticides with long residuals. But in small cotton, experience shows this may not be the case.
“None of the miticides are systemic and as the plants put on new leaves, they're unprotected and can re-infest later if more mites move into the field.”
In Louisiana, spider mites are showing up in the same areas they've preferred for the last three years: chiefly, near the Mississippi River levee. Bagwell says the worst cases are in Madison Parish but Tensas Parish is also having mite trouble.
There is good news, says Bagwell. “After dealing with the pest so much lately, most consultants and growers in mite country know what to do. Now, everyone is more likely to weigh the consequences and chances for flaring mites.”
Any miticide use is considered very carefully, says Bagwell. “Miticides are expensive. A couple of years ago it was hard to get a farmer to swallow the idea that a $25 application was necessary. Now, it's a whole lot easier to suggest. They've been through the mite battles — spent well over $100 per acre for control in some cases — and now know an expensive miticide is a lot simpler and easier.”
Yes, a miticide can be an expensive solution, says Lorenz. “But, at the end of the day, they can be cheaper then chasing mites around all season. If you don't make the right call on spider mites, they'll hang around and come back with a vengeance. I've seen that repeatedly. This pest can be bad, bad news.”
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