THRIPS RESISTANCE HAS been confirmed to the neonicotinoid cotton seed treatments. Once cotton reaches the fifth true-leaf stage, it’s beyond the point of economic damage from thrips.
Cotton producers in Alabama – like those in the MidSouth and in other parts of the Southeast – found pockets of thrips resistance with their at-plant treatments in 2014.
“We’re definitely in the middle of some changes with thrips resistance,” says Ron Smith, Auburn University Extension entomologist. “Some of these changes are part of a trend, and some of them might be different this year with weather conditions and other factors.”
Smith says there are several questions that need to be answered about thrips resistance in cotton.
“What do we know about thrips resistance, and how to we manage the seed treatments for the longest term possible? And, what are we doing to do if we get even greater resistance?”
With Temik no longer on the market, farmers have relied on two neonicotinoid seed treatments, Cruiser (thiamethoxam) and Gaucho (imidacloprid), to control insects that infest fields as cotton emerges.
Smith’s colleague, Extension Entomologist Tim Reed, says thrips resistance has been confirmed to the neonicotinoid seed treatments. Thirty-two thrips populations from 10 states, including Alabama, were analyzed by North Carolina State University, he explains.
“Those findings concluded there was a level of resistance to Cruiser – about 11 times greater than the non-susceptible population, and the level of resistance to Gaucho was about 4.9 times greater than the non-susceptible population.
“So we had resistance to both Cruiser and Guacho, but for the populations submitted, resistance was greater to Cruiser. Populations came from wheat, cotton and weeds, and resistant thrips were found in all three scenarios. It didn’t matter if they came from late-season cotton or early season weeds, they still saw the resistance issue,” says Reed.
In the three populations submitted from Alabama, he says, the level of resistance was low to moderate. Samples were taken from Belle Mina, Prattville and Headland, representing the northern, central and southern portions of the state, respectively.
“This thrips resistance issue is spotty,” says Reed. “We looked at in-furrow treatments last year, and in my tests at Belle Mina, we saw a little more damage to cotton that was treated with Cruiser than with Gaucho. In the Prattville tests, the same level of damage occurred in both treatments. It’s not a real bright picture now for the neonicotinoids as a seed treatment on cotton, and the long-term outlook is not positive at this point as far as efficacy.”
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