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Tests show zebra chip in Idaho field


Researcher urges preventive spraying and monitoring


By JOHN O'CONNELL


Capital Press


TWIN FALLS, Idaho -- Adult potato psyllids captured on sticky cards at the edge of a Twin Falls County commercial spud field have tentatively tested positive for the Liberibacter bacteria that causes the crop disease zebra chip.


If the results stand, they would be the first infected psyllids discovered this season in the Pacific Northwest.


Zebra chip, which reduces crop yields and leaves bands in tuber flesh that darken when fried, first arrived in the Pacific Northwest last season. The disease is spread by potato psyllids, tiny aphid-like insects. Potato farmers have implemented extensive and costly psyllid monitoring and pesticide programs this season, hoping to protect their crops from the new threat.


The samples were collected June 19, and the tests were conducted by Alexander Karasev, an associate professor of plant virology at University of Idaho.


Aside from the cards, Erik Wenninger, an assistant professor of entomology at U of I leading the group of scientists responsible for Idaho's monitoring program, said no other evidence of psyllids at any life stage was found in the field. However, Wenninger discovered psyllid eggs on adjacent bindweed plants.


He explained the grower had sprayed the field for psyllids a couple of days earlier, and the treatments were apparently effective. Wenninger believes controlling weeds could also help protect growers.


Psyllids have also been discovered on Idaho greenhouse plants and in fields in Oregon and Washington, though all other samples tested so far have tested negative for Liberibacter.


Karasev said the initial tests were done through a method known as a preliminary chain reaction. Follow-up testing will be done via genetic sequencing, which he said is somewhat more sophisticated.


Karasev said the preliminary results were made public, though unconfirmed, due to the importance of the issue.


"So far we have an initial unconfirmed positive. For me it's a new pathogen. I am learning in the process," Karasev said.


He said follow-up testing will be delayed due to the July 4 holiday.


Phil Hamm, an Oregon State University plant pathologist who has conducted extensive zebra chip research, believes the possible discovery affirms the importance of preventive spraying and monitoring by growers.


"You can't prevent Liberibacter-infested psyllids from getting in your field. You just don't want them laying eggs out there and you don't want them established," Hamm said. "The worst that could happen to you (if you spray) is you'll have a little bit of incidents out there, but it won't knock you out of grade."


Hamm is also optimistic that recent hot weather may force the psyllids to migrate further north, sparing the region from a repeat of last year's damage.



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