KIMBERLY, Idaho — Potato growers throughout Eastern Idaho are starting insecticidal programs to protect their crops from zebra chip disease following the recent confirmation of potato psyllids in the region.
The tiny, winged insects can harbor the Liberibacter bacterium that causes zebra chip — a crop disease that forms bands in tuber flesh that darken during frying.
The University of Idaho has conducted an extensive potato psyllid scouting program since 2012, which was the season after the disease first surfaced in the Pacific Northwest.
During the week ending July 2, UI Extension entomologist Erik Wenninger, who administers Idaho’s monitoring program, said psyllids were found in a quarter of the 97 fields where sticky traps have been deployed to capture the pests.
The cards contained 48 psyllids, including from a field in Bingham County and a field in Power County in Eastern Idaho, where psyllid pressure has been light compared with other parts of the state.
The monitoring program also detected psyllids in a dozen fields in Canyon County, three fields in Payette County, two fields in Owyhee County, two fields in Twin Falls County and one field each in Elmore County, Ada County and Malheur County, Ore.
“I know a lot of growers have been waiting until we report psyllids in their area until they start spraying, which in a lot of cases has saved growers a lot of sprays,” Wenninger said. “If a grower is inclined to start spraying when we detect psyllids in their area, I think that’s a reasonable course of action.”
Wenninger said infected psyllids were confirmed from Canyon County samples in late May, but all samples tested since then have been negative for Liberibacter. Test results have not been returned from the most recently captured psyllids. It takes about three weeks from infection for zebra chip symptoms to surface — including aerial tubers, leaf rolling, purplish discoloration, yellowing leaves and swollen nodes.
“It was a little bit surprising to see (psyllids) show up that early in Eastern Idaho, but not terribly surprising,” Wenninger said.
Wenninger said the recent hot, dry weather has favored psyllids. During last season, which was also unseasonably hot, the first psyllids also arrived during the first week of July.
Aberdeen, Idaho, grower Ritchey Toevs applied insecticide in-furrow at planting and plans to move up his first foliar insecticide spray by nine days to July 11, due to the recent detection of psyllids in Eastern Idaho.
“With my next fungicide application I’ll need to add (insecticide),” Toevs said.