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Potato psyllids increase in the Northwest

Aug. 18, 2015, Moses Lake, WA – The potato psyllid is being seen in rapidly growing numbers across the Pacific Northwest, but few so far have been found to carry a potentially devastating disease.

Earlier this month, Washington State University Extension researchers found the bugs on 79 per cent of field samples throughout the Lower Columbia Basin, up from 60 per cent the week before and 50 per cent the week before that. Each sample contained an average of 3.1 psyllids, up from 0.6 the week before.

The psyllids, which feed on potato leaves, “are a big deal because they can transmit a bacterium to potatoes that causes zebra chip disease,” said Carrie Wohleb, a WSU professor and regional vegetable specialist in Moses Lake.

Infected potatoes develop brown lines, like zebra stripes, that are most apparent when fried. The striped sections easily burn and caramelize, leaving a bitter flavour. Though there are no known health risks, the potatoes are unusable for chips or french fries.

Zebra chip disease wasn’t seen in the Northwest until 2011 and is relatively rare there, but it can cause huge damage, Wohleb said. She has monitored psyllids since 2012 and said she has never seen this many before.

Wohleb and her colleagues are testing the psyllids they collect for the zebra chip bacterium. So far, fewer than one per cent of the bugs tested this year have been carriers of the disease. Zebra chip causes symptoms similar to other diseases and so is difficult to diagnose.

Wohleb recommends that farmers use insecticides to help control the pests.

“It can be a total loss of a crop,” she said. “Since potatoes require such a large investment, that’s a big deal. That’s why we recommend spraying for the psyllids.”

“It is a complicated situation,” she added. “We don’t completely understand where the psyllids spend the winter and where they pick up the bacterium, for example. But we’re working to figure out how we can best help farmers protect their potato crops.”

The psyllid is just one of the insects Wohleb and others in a statewide potato insect monitoring network observe.

Here in Canada, a major, multi-agency project has established a nation-wide monitoring network for zebra chip and the potato psyllid. Click here to read Potatoes in Canada’s reporting on the project.

August 18, 2015  By Potatoes in Canada