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Higher Risk of Zebra Chip Predicted in Washington State

Wednesday Aug 25, 2021

As originally appeared in, Capital Press - 8th July 2021

Washington potato farmers will need "extra vigilance" monitoring and managing their fields for potato psyllids and signs of zebra chip disease, experts say.

All psyllids collected as part of Washington State University's insect monitoring network are sent to a USDA Agricultural Research Service lab in Wapato to see if they carry Candidatus Liberibacter solanacearum, or LSO, the bacteria that causes the disease zebra chip.

The infection rate is normally low in the Columbia Basin, said Carrie Wohleb, regional vegetable crops specialist for WSU Extension in Moses Lake.

"In 2016, I collected about 30,000 potato psyllids and two of them were infected with LSO," Wohleb said. "But this year, we're looking at 13 LSO-infected psyllids out of 149 tested so far."

Infected psyllids have been collected from several parts of the Columbia Basin, including fields near George, Black Sands west of Moses Lake, Mattawa, Othello and Pasco.

A little zebra chip occurs in the Columbia Basin each year, but the region has a lower infection rate compared to other parts of the country, Wohleb said.

"We want to make sure we control any of those psyllids as they're entering the potato fields," she said.

Wohleb encourages farmers throughout the region to monitor psyllid numbers.

"We recommend a no-gaps control with an insecticide program," she said.

Immature life stages of the psyllid, such as eggs or nymphs, on the leaves of the outside edges of a field indicate an adult psyllid has established a new population.

"That's when you really want to get it under control," Wohleb said.  

Researchers originally thought psyllids might not transmit LSO as readily in high heat, said Tim Waters, WSU Extension regional vegetable specialist in Pasco. But the opposite appears to be occurring this year.

"It very well could be that psyllids, because of the host plants they're feeding on, under drought conditions ... likely began moving off of their overwintering hosts earlier than normal," Waters said. 

USDA ARS researchers have been studying the alternate host plants the psyllids use before moving into crop fields. 

Waters isn't aware of any zebra chip occurring in potato fields yet.

"We've had seasons where we've had these higher psyllid numbers, but we really haven't had seasons with high psyllid numbers with a high percentage of LSO," he said. "That's the part that's unnerving right now."

Farmers may need to make a faster decision to spray insecticide than the researchers might have recommended in more recent years, Waters said.

"Zebra chip is a manageable disease, as long as we're controlling (psyllids) as they move into the fields," Wohleb said. "I am concerned about those growers that do allow it to slip through the cracks, maybe don't see symptoms in their field and then find out too late."