In 2007, information from the Cotton Foundation and Mississippi State University showed that thrips cost growers 145,040 bales. That put thrips squarely in third place as the most damaging cotton insect pest behind the bollworm/budworm complex (229,186 bales) and tarnished plant bugs (171,478 bales).
But what must be considered is that thrips have a much smaller window of damage potential than either of the others, making it potentially the most damaging early season insect. Thrips can damage cotton from emergence to around the 5-leaf stage, and they feed on leaf surfaces, leaf buds and small squares.
“Thrips are an annual pest and we are basically going to have them on every acre,” says Dr. Phillip Roberts, Associate Professor of Entomology at the University of Georgia. “Thrips are just so predictable and consistent.”
But because of that, there is very little left unanswered on how to control thrips.
“We haven’t had the severe losses you might imagine from thrips for a couple of reasons,” says Dr. Roger Leonard, a Louisiana State University AgCenter entomologist. “Practically 100% of our acreage receives a seed treatment or Temik at planting. That’s a preventive strategy. In addition, many of our acres are sprayed with a single foliar application that is triggered on the presence of thrips on immature seedlings with fewer than five leaves.”
Roberts says approximately 90% of Georgia’s cotton acreage receives an at-planting treatment for thrips: “We encourage growers to use a preventative treatment at planting like Avicta Complete Pak, Cruiser, Gaucho Grande and Temik. Any of these.
“It’s very important to protect seedlings as they develop,” Roberts continues, “but it’s rare that we would have to treat for thrips after the 5-leaf stage.”
No Automatic Sprays
There are many foliar insecticides with excellent activity on thrips, but growers are cautioned not to automatically apply a thrips material with the first application of glyphosate: (1) They are ineffective and wasteful if thrips are not at economic thresholds, (2) they can flare other pests, and (3) they can be hard on beneficials.
“We discourage people from making an automatic foliar spray because it will disrupt beneficials,” says Roberts. “But the point is, if we have an issue with thrips, we need to address it. Unfortunately we do not have a foliar product that will control thrips without killing beneficial insects.”
Another point to consider is that cotton is often described as being a great compensator. “We do see injury, but fortunately have enough season left in Louisiana to compensate for most of the minor damage,” says Leonard. “When our soils warm up and cotton jumps out of the ground and starts growing, thrips do not affect our crop as much as they would in Arkansas and Tennessee.”
Wheat, Wheat and More Wheat
This season could bring a new challenge in thrips control, particularly in Louisiana, Mississippi and Arkansas where wheat acreage has nearly tripled since 2006. Wheat is an excellent host for thrips, and cotton adjacent to maturing wheat could see higher than normal thrips pressure, especially after on-seed treatments and Temik have played out.
“It’s hard to predict what an insect is going to do, but generally we are going to have high thrips numbers with the amount of wheat acreage we have in the state,” says Mississippi Extension entomologist Dr. Angus Catchot. “There’s not a lot of things we can do preemptively at that point, but you need to be aware of it.”
Depending on the weather conditions and crop progress, tarnished plant bugs and spider mites can also present early season problems.
Plant bugs, which were devastating late-season in parts of the Mid-South in 20007, can be nearly as problematic early season. At high population levels, terminal feeding may result in “crazy cotton,” where the main stem no longer dominates branch growth.
Spider mites are more closely associated with extreme heat and inadequate moisture later in the season, but have been showing up earlier for the past several years. They feed on epidermal cells on the underside of cotton leaves, resulting in moisture loss and drying of the damaged leaves. The damage can also disrupt photosynthesis.
Regional Thrips Losses
Beltwide Insect Losses
Source: Cotton Foundation/Mississippi State University
Source: University of California
Source: North Carolina State University
Source: Penn State University
“Crazy cotton” is the result of plant bugs damaging the main terminal.
Source: University of Tennessee