Disease-carrying potato psyllids increase in the Northwest

potato-80MOSES LAKE, Wash. – The potato psyllid insect pest is being seen in rapidly growing numbers across the Pacific Northwest, but few so far have been found to carry a potentially devastating disease.

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

Hold the chips and fries

Carrie Wohleb

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 flavor. 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 here, but it can cause huge damage, Wohleb said.

Insecticides recommended

She has monitored psyllids since 2012 and said she has never seen this many before.

Zebra chip disease causes brown stripes that darken and turn bitter when fried, making the potatoes unusable in chips or fries.

She and her colleagues are testing the psyllids they collect for the zebra chip bacterium. So far, fewer than 1 percent 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.

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

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

Still learning about the pest

“It is a complicated situation,” she said. “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. The potato growers of Washington, through a grant from the Washington State Potato Commission, fund the network.

Growers can contact Wohleb at cwohleb@wsu.edu for more information about potato psyllids and zebra chip disease. The network also provides potato pest alerts via email; contact Wohleb to be added to the distribution list.


Carrie Wohleb, WSU Extension professor/regional vegetable specialist, 509-754-2011 ext. 4313, cwohleb@wsu.edu