Courtesy of Erik Wenninger
Entomologists say Northwest spud growers should be mindful of recent research showing potato psyllids in Texas have developed resistance to neonicotinoid insecticides.
“It’s an extremely important finding,” said Oregon State University Extension entomology specialist Silvia Rondon. “This should be a wakeup call for growers in the PNW regarding the potential for psyllids here to develop resistance to pesticides.”
Potato psyllids can harbor the Liberibacter bacterium, which causes a crop disease called zebra chip that results in tuber-flesh patterns that darken when fried. The disease first surfaced in the Northwest in 2011.
The recent study, by Texas A&M AgriLife Research entomologist Ada Szczepaniec, still awaits publication. Szczepaniec collected hundreds of pysllids, starting in 2015, from large potato fields in the Rio Grande Valley, Weslaco and near San Antonio. She bred the psyllids and tested progeny for heritable resistance.
Szczepaniec found between 60 and 95 percent of the tiny, winged insects she bred survived treatments with four different doses of imidacloprid and thiamethoxam.
Neonicotinoid use in Texas and Mexico has been on the rise since psyllids were identified as vectors of zebra chip in 2005. Szczpaniec said growers still have other effective chemistries to control psyllids. Northwest growers face considerably less psyllid pressure than Texas growers, she said.
Szczepaniec wasn’t surprised by her findings. John Trumble, an entomology professor with University of California-Riverside, confirmed psyllids with resistance to imidacloprids from Weslaco in a 2013 paper. But Szczepaniec’s new research shows thiamethoxam resistance has also developed, and resistance is statewide.
Trumble has encouraged California growers to apply neonicotinoids to potatoes only through a drip line to improve efficacy and prolong the onset of resistance.
“I would be extremely cautious about any foliar applications,” Trumble said.
Washington State University regional vegetable specialist Tim Waters said about 95 percent of the potato acres in his state have neonicotinoids applied at planting to help control other pests, and he advises those growers against using the class on any subsequent foliar applications.
University of Idaho Extension entomologist Erik Wenninger is setting up sticky traps as part of an extensive psyllid scouting program. Wenninger said no psyllid resistance studies have been conducted in the Northwest, and he believes the time has come to collect such data. For now, he advises growers to limit foliar neonicotinoid sprays.
“We’d be in huge trouble if we lost neonicotinoids,” Wenninger said, adding the class is also vital in controlling aphids and Colorado potato beetles.