Specialist says all growers in the region should treat if psyllid found in one field
By JOHN O'CONNELL
Researchers say populations of potato psyllids -- vectors of zebra chip, a crop disease new to the region -- are growing dramatically in the Columbia Basin.
"The psyllid is showing up in a lot of places in the Columbia Basin, and in some traps in very high numbers," said Andy Jensen, an entomologist who coordinates research for the Oregon, Washington and Idaho potato commissions.
Zebra chip, which arrived for the first time in the Pacific Northwest last season, is caused by the Liberibacter virus. It reduces potato yields and renders tubers unmarketable with bands that darken when fried.
Despite the increasing psyllid pressure during the past couple of weeks, Phil Hamm, an Oregon State University plant pathologist, believes the disease shouldn't cause major problems for growers who stick with insecticide programs.
"You cannot stop them from coming in your field, but you better not let them colonize," Hamm said. "I expect we'll see additional numbers of psyllids in the next three weeks."
Hamm said six to eight fields in the Columbia Basin have a few confirmed positive plants, and many more undoubtedly harbor the disease at insignificant levels.
In Idaho, psyllids have been concentrated in Magic Valley. Three psyllids found in Bonneville County in eastern Idaho tested negative for the virus.
The University of Idaho recently obtained permission from the Idaho Potato Commission to redirect revenue it allocated for zebra chip research toward additional testing, having received more samples from growers than anticipated.
Nora Olsen, a University of Idaho Extension potato specialist, said Idaho discovered zebra chip later than Washington and Oregon last season and is continuing with extensive psyllid testing to catch up in answering basic questions.
"We've got another month being out in the field. Now we're collecting a lot more tuber samples, too," Olsen said.
U of I is also conducting insecticide trials to help growers hone their zebra chip programs next season.
Hamm said demand for testing has been higher than predicted in all three states. He worries the testing is driven by growers seeking field-specific data, which he argues misses the point.
"When the region has psyllids, you treat," Hamm said.
Jeff Miller, who provides free psyllid testing on behalf of Miller Research in Rupert, Idaho, has seen positive potato plants in fields where few psyllids have been detected on sticky traps used to monitor them.
"The method we're using to estimate the populations, we understand that method is not foolproof anyway, but I would expect it would do better than it is," Miller said. "In Minidoka County, we only found two psyllids, yet it appears we've got several fields that have known zebra chip symptoms."
Jensen said the USDA in Washington is working to develop an effective pheromone to attract psyllids to traps, which growers should use in tandem with field scouting.
If there's a silver lining to zebra chip, crop consultant Tim Praegitzer of Hazelton, Idaho, believes it has made growers -- forced to regularly spray insecticides anyway -- better about applying fungicides.