A wake-up call
Even if these insecticides are still providing you with long residual control, the documented cases of resistance should serve as a wake-up call to adhere to strict insecticide resistance-management recommendations, Rogers says.
“Make sure you put out a good, robust rate at planting,” he says of Admire Pro. “When the residual begins to wear off, switch to a foliar compound with an alternate mode of action.”
Imidacloprid, thiamethoxam, dinotefuran (Venom) and acetamiprid (Assail) are neonicotinoids that all belong to the Insecticide Resistance Action Committee’s Group 4A.
Most of the major manufacturers prominently list the IRAC group number or numbers on the pesticide label, Rogers says. This can simplify resistance management because users can simply rotate to a compound with another IRAC group number.
Gradual decline in residual activity
John Palumbo, a research entomologist with the University of Arizona in Yuma, has been tracking whitefly sensitivity to imidacloprid for 11 years in broccoli plots and 16 in lettuce. He’s seen a steady increase in imidacloprid resistance in the past five to six years.
“It’s not the same product as it was when it [first] came out,” he says. “It doesn’t have the residual effects in broccoli and cole crops.” In his broccoli plots, for example, Palumbo says he sees a steady decline in control after 20 days.
“By 40 days, it’s like it’s not there any more. It’s no different than the untreated control,” he says. “Down here, it’s just we’re not seeing the control we used to get of 45 to 50 days. We’re lucky [now] if we get 25 days control.”
In fact, one of Palumbo’s broccoli-imidacloprid trials this year was “pretty much blown out,” so the pest control adviser had to come over the top with Movento to rescue the crop, he says.