Submitted by Jeff Miller
Potato farmers throughout Idaho have significantly scaled back their insecticide programs amid a second consecutive season of light pressure from the winged psyllids that spread the crop disease zebra chip.
Many growers say they’ve been influenced to put off spraying, at least until psyllids arrive in their areas, by lower-than-desired processing contracts and basement fresh prices. Zebra chip — caused by the liberibacter bacterium, which sullies tuber flesh with bands that darken when fried — was first detected in the Pacific Northwest in 2011.
University of Idaho researchers, who have organized statewide field monitoring each season since the disease’s arrival, confirmed this summer’s first and only liberibacter-positive potato psyllid on July 23 from a sticky trap in a Canyon County spud field. Last summer, UI had confirmed three positive psyllids, all from Canyon County, by the first week of July.
“Now is the time to step up local monitoring and management programs in the area,” UI advised in a grower alert following the recent confirmation of a positive psyllid.
UI research technician Amy Carroll said about 20-30 psyllids have been trapped this season, including one as far east as Power County, with test results for liberibacter still pending on some samples.
In 2012, 30-50 percent of psyllids that were captured tested positive for liberibacter. Carroll said this summer seems comparable to last season, when just 3 percent of more than 1,000 captured psyllids tested positive and little crop damage was reported.
“We have fewer psyllids this year, and we’ve been monitoring about the same amount of fields with sticky cards,” Carroll said. “Usually it does pick up about August, and it has been picking up.”
Wilder grower Doug Gross applied a second round of insecticides shortly after the discovery of the infected psyllid. Nonetheless, he’s scaled back investment in his prevention program from about $220 per acre to roughly $75 per acre this season. He acknowledges he’s taking a risk but remains hopeful 2012 was a fluke.
“With the value of our contract we had to cut somewhere,” Gross said. “We did wait longer (to apply insecticide) and we are using less expensive quick-kill insecticides rather than the systemic type of insecticides.”
Mike Larsen, manager with Grant 4D Farms in Rupert, estimates he’s cut his spraying program in half this season, emphasizing high-risk fields near water where psyllids have been found in the past and relaxing applications on other fields. Liberibacter tests are still pending on a single psyllid found on his farm a few days ago.
“I think many of us are relying more on the monitoring program before we go out and just spray,” Larsen said. “When your contracts are not what they used to be, you sure look at areas you can cut, and there’s a lot of dollars sitting there.”
Jim Tiede, of Power County, is still waiting for psyllid populations to build before spraying.
Jeff Miller, whose Rupert-based crop research business has assisted with psyllid monitoring and chemical trials, believes a wait-and-see approach is appropriate outside of high-pressure areas such as Filer and Canyon County. He advises less expensive foliar chemicals, such as abamectin, may suffice, but he warns growers against following neonicotinoid seed treatments with the same class of foliar insecticides to avoid resistant insects.