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Farmers Get New Tool Against Cotton Pests

South Carolina cotton farmers now have a new tool to use in their fight against thrips. Jeremy Greene, Clemson professor of entomology at the Edisto Research and Education Center, said Clemson and North Carolina State University researchers have developed an online tool - Thrips Infestation Predictor for Cotton (TIP).

"Thrips are common pests that cotton growers can be assured they will find in their crops ever year," Greene said. "We developed this tool for cotton growers to use in helping make informed decisions concerning thrips management."

Found at http://climate.ncsu.edu / Cotton TIP, the Thrips Infestation Predictor uses weather data to make predictions of thrips dispersal timing, cotton growth affecting seedling susceptibility and injury risk that results from thrips dispersal and seedling susceptibility occurring at the same time.

Altering planting dates can be a great cultural control strategy for mitigating injury from thrips in seedling cotton. Planting later in the normal planting window (late April into early June) is often the best strategy for minimising risk due to thrips. Growers will learn more about this new tool during production meetings this spring.

Thrips cause most damage to seedling cotton. Leaves may turn brown on the edges, develop a silvery colour, or become distorted and curl. Light thrips infestations tend to delay plant growth and retard maturity. Heavy infestations can kill terminal buds or even entire plants. Damaged terminal buds cause abnormal branching patterns.

Greene advises growers to use a preventative, at-plant application of insecticide for thrips and to begin foliar insecticide treatments when two or more thrips per plant are found and damage is present, paying particular attention to the presence of immature thrips.

Other important pests of cotton are the bollworm, Helicoverpa zea, stink bugs (various species), and the tarnished plant bug (TPB), Lygus lineolaris. Bollworm is mostly controlled by Bt technology and planted on almost every acre in South Carolina.

But some escapes are common and are addressed with additional applications of foliar insecticides. Issues with resistance to Bt proteins and pyrethroid insecticides are becoming more apparent with bollworm. Greene said more research and revised recommendations are forthcoming about those developing problems. "Stink bugs remain our number one group of pests of cotton in South Carolina," Greene said.

Previous work by Greene and a team of entomologists in the southeastern United States called the Southeast Row Crop Entomology Working Group (SERCEWG) provided growers with a dynamic boll-injury threshold. Greene said this research has served growers well. But another insect is gaining momentum.

Recently, the tarnished plant bug has gained more traction in the southeastern United States as a mid-season pest. Greene said the tarnished plant bug has always been found in cotton in our region, but was never a major pest.

"We see the species in cotton crops but seldom in numbers justifying intervention with insecticides," Greene said. "However, tarnished plant bugs are seen in selected fields every year."

Tarnished plant bugs typically cause problems in June and July. They can puncture small bolls, inflicting damage symptoms similar to those caused by stink bugs, including: lint attached to seed coats acquiring a yellowish to brownish stain and small wart growths developing on the inside of boll walls to mark the location of penetration.

Damaged bolls may open prematurely or become hard-locked. Greene advises growers to ensure that all bolls examined are of the same age class.

If damage symptoms are present, Greene said to look for adults and large nymphs by shaking plants over a beat cloth or into a plastic pan, or using a sweep net where insects can be examined and identified. Published recommendations for controlling these insects and others in cotton can be found in the Cotton Insect Management section of the 2018 South Carolina Pest Management Handbook.