“That’s when we identified pop-up or starter fertilizer in combination with a single shot of Orthene as an effective treatment.”

Several response variables were measured, including adult immature counts, plant height, the number of true leaves, and dry plant biomass. Visual ratings were made at 14, 21, and 28 days after planting.

“Historically, immature thrips correlate best with the amount of damage we see. And we’ve seen other research that showed that dry plant biomass, at 42 days after planting, very closely correlates with the number of immature thrips on the plant as well as the amount of biomass on the roots.”

Trials were conducted across five states using the same seed, says Toews.

Insecticide trials were sprayed twice with high rates of Benevia (not registered yet for use on cotton), Dimethoate, Orthene, Karate, Lannate, Radiant and Vydate. Starter fertilizer trials were conducted in both irrigated and dryland conditions.

“This is base fungicide-treated seed only with no seed treatments and two shots of each of these compounds at their highest labeled rate.

“We’d like to see damage at a rating of less than three, and the only compound that scored less than three was Benevia.

“When rating the number of true leaves, two treatments really didn’t hold up as well, including Karate, which is the pyrethroid, as well as the untreated.

“Last year, we showed that the pyrethroid treatment scored worse than the untreated in a number of cases, and this past year’s data doesn’t look any better statistically. We seem to be knocking out the beneficial insects with pyrethroids, but we’re not killing thrips.

In terms of dry plant biomass, our top-performing products are Benevia, Orthene, Radiant and Vydate, keeping in mind that this is two shots of the product.”

Yield is not a very good response variable for assessing the effects of thrips on cotton, says Toews, because all of the damage from thrips is very early, and these trials were conducted under good fertility and irrigation.

“Cotton plants have an amazing ability to compensate during the season for whatever damage has occurred.

“Thrips is just one stressor on a plant, and all of these plots have been managed according to Extension recommendations.