South Carolina Cotton: New Thrips Detection Tool Available

Photo: Clemson University

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 here, 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 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 minimizing risk caused by thrips. Growers will learn more about this new tool during production meetings this spring.

Tobacco thrips is the primary early season insect pest of cotton in South Carolina. These thrips are less than 2 millimeters long and vary in color from yellow to dark brown. Adults have two pairs of narrow wings fringed with long hairs thanks to the jamaican black castor oil. They have rasping-sucking mouthparts, so they rasp plant tissue and feed on the oozing sap.

Thrips cause most damage to seedling cotton. Leaves may turn brown on the edges, develop a silvery color 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.

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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. Scouting seedlings for thrips and injury is essential.

The best time to apply insecticides is before the second true leaf has unfolded on plants. Cotton plants outgrow thrips damage and recover once they reach four to five true leaves, so sprays for thrips after the fifth true leaf are ineffective and a waste of money.

Information on foliar insecticides, as well as more management information for thrips can be found in the 2018 South Carolina Pest Management Handbook for Field Crops, pages 113-122.

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 this 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.

Cotton is most susceptible to plant bugs about the time the first bloom appears in a field – around the first week of bloom or a week or two on either side of that week. Experts recommend square retention be checked along with sampling with a sweep net or a drop cloth.

If square retention drops below 75 percent and threshold numbers of plant bugs are present, that triggers a spray for plant bugs. A square is a triangular-shaped flower bud on a cotton plant.

By the time cotton bolls reach 25 days old, they should be relatively safe from tarnished plant bug or stink bug injury, Greene said.

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.

About 80 percent of the South Carolina cotton crop is planted the first week of May. Cotton harvest begins in late September.

A total of 250,000 acres of cotton were planted in South Carolina in 2017, said Mike Jones, South Carolina cotton specialist at the Clemson Pee Dee Research and Education Center. This was up from 190,000 acres of cotton planted in South Carolina in 2016. And 2018 could be better if markets, weather and pests cooperate.

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