By JOHN O'CONNELL
Three potato psyllids captured in separate Idaho fields have tested positive for the Liberibacter bacterium that causes the crop disease zebra chip in potato fields, University of Idaho researchers announced July 16.
The infected psyllids were caught on sticky traps surrounding two Canyon County fields and one involved in insecticide trials at UI's Kimberly Research and Extension Center. They were the first psyllids to test positive for Liberibacter in the Pacific Northwest, though several clean psyllids have also been captured in the Columbia Basin.
As of July 17, UI Extension entomologist Erik Wenninger said 26 of 36 psyllids captured under Idaho's expanded potato psyllid scouting program had been tested, with all others confirmed as negative.
"So far, most of them have come from Canyon County," Wenninger said of the distribution of psyllids. "Our earliest psyllid detections have been primarily in western Idaho -- Canyon County and Ada County. We've had a few in Elmore County, several in Twin Falls County and just one in Cassia County. That's the furthest east we've detected psyllids."
Zebra chip, which creates bands in tuber flesh that darken when fried, was first discovered in the Pacific Northwest in 2011.
Wenninger said psyllids have been found overwintering in the Columbia Basin and western Idaho, and the first detections of this season may have come from a resident population. He also reported a psyllid found in March on a sticky card by a sticky nightshade plant in the Twin Falls area, suggesting they may also be overwintering in Magic Valley.
The first psyllid detected through field scouting efforts this season, captured in western Idaho, came at about the same time as last season. However, some of the earliest psyllids found last season were positive for the bacterium.
"This year it's taken a few weeks before we've found a positive," Wenninger said. "That's my hope that we are detecting the first occurrence of psyllids in different areas, and hopefully management programs are implemented in a timely manner to limit the impact of zebra chip."
As was the case last season, detections have started out slow. Wenninger expects psyllid pressure will increase dramatically in August and September.
Wenninger said it's common for just 1-4 percent of psyllids to harbor the bacterium, and a 10-15 percent infection rate is considered extremely high among the states that deal with zebra chip.
Though just one or two of the thousands of psyllids tested in Columbia Basin proved to be positive last season, he said zebra chip was found in the region's field's, nonetheless.
Growers in eastern Idaho learned they're not immune from zebra chip on March 12, when UI announced potatoes taken from storage in Power County contained the disease.
Wenninger advises growers to continue monitoring their fields for psyllids and to have their insecticide programs in place if any psyllids have been detected in their areas.