The unrelenting rains of 2013 made for less-than-ideal conditions when it came to conducting certain on-farm research in the Southeast, but trials in North Carolina and Georgia confirmed what has been observed in earlier work on cotton thrips injury.

According to a survey conducted this past year of independent crop consultants, thrips have the potential to be the most damaging insect pest of cotton, with average control estimated at $24.50 per acre – $15 to $18 for the seed treatment and $8 for the foliar spray.

In research presented at this year’s Beltwide Cotton Conferences in New Orleans, Dominic Reisig, North Carolina State University Extension entomologist said the objective of his experiment in 2013 was to determine if cotton can compensate for early season thrips loss later in the season by manipulating moisture through tillage and irrigation.

It was a very bad year, he said, to conduct an irrigation study in North Carolina, where heavy rainfall routinely washed out fields in 2013. Still, some earlier observations about thrips were confirmed.

“The injury we see from thrips is from the insect piercing the leaf as it’s emerging out, with the leaf often being misshapen. Sometimes you won’t actually see this in terms of a reduction in the plant weight itself. The plant may maintain some of its mass, but it’s just not getting the adequate leaf surface area to get the photosynthesis required to grow properly,” he says.

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Research from the University of Georgia’s has shown, he says, that a seed treatment of Cruiser and a foliar overspray of Orthene will increase the cotton plant’s dry weight compared to when there is no treatment. “That’s essentially a one-to-one relationship – what you’re seeing above ground is mirrored below ground. When your fruits are hammered above the ground, there’s less root mass,” says Reisig.

Other work in Georgia has shown a relationship between the amount of cover and the density of thrips, he adds. “So basically, when you start to till and reduce the amount of cover, you tend to have more thrips density.”

The question of his research, says Reisig, was whether or a factor such as moisture later in the season could compensate for thrips loss.

“So even though we’re having this reduction of root mass, can we make it up by providing the plant with moisture later in the season? Factors we looked at in this study were irrigation – we looked at irrigated and non-irrigated. We also had three different types of tillage – conventional, strip-till and reduced till. We also had treatments with an insecticide and with no insecticide. My insecticide plots had a base seed treatment and a foliar overspray, with the foliar overspray being made at the second true-leaf stage.”