Published online: Sep 14, 2011 Fungicide
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Zebra chip, a disease that annually costs Southwest U.S. potato growers millions of dollars in crop loss, has been found in Washington and Oregon.

A USDA scientist and an Oregon State University plant pathologist confirmed zebra chip in tuber samples growers submitted to the OSU research laboratory in Hermiston, Ore.
Phil Hamm, plant pathologist at the Hermiston research station, submitted the samples to the USDA lab in Prosser, Wash., after finding they were infected by the zebra chip pathogen.

"Because of its importance, we asked that Jim Crosslin with the USDA in Prosser confirm our lab results," Hamm said.

Hamm said the disease was identified in five different fields in the southern Columbia Basin, and in five cultivars: Russet Ranger, Russet Norkotah, Pike, Alturas and a red selection.

"I don't think there are any catastrophic issues out there," Hamm said, "but there is some damage."

The disease has not been found in Idaho.

Researchers do not know if the disease develops or spreads in storage, but Hamm is advising growers who plan to store potatoes to scout and treat for the psyllid if they find symptoms and green tissue is present.

"It is better to err on the side of caution," Hamm said.

Zebra chip is caused by the Liberibacter bacteria, which potato psyllids transmit to potato plants through feeding.

Researchers also are unsure if the disease poses a long-term threat to the area's potato industry. That will depend in large part on whether the psyllid overwinters in the Northwest.

"It doesn't appear they do," Hamm said, "but if they do overwinter and maintain the bacterium, it could be a huge issue."

In warmer climates where the psyllid is know to overwinter, such as Texas, growers treat on average 12 times a year to control the insect, Hamm said.

In the Northwest, potato psyllids typically don't appear until mid- to late-season, Hamm said.

Tubers infected with the disease develop black stripes, similar to zebra markings. Foliar symptoms include yellowing, wilting vines. Infected plants die relatively quickly, Hamm said.

Hamm recommended using a combination of products if treating for the psyllid to maximize control of adults and eggs.

"Be watchful of PHI (pre-harvest interval) on anything applied," Hamm said.

-Source, Mitch Lies, Capital Press