By MITCH LIES

Capital Press

Oregon State University reports that zebra chip has been found in two potato plants from a single field east of Hermiston, Ore.

The discovery comes despite low trap counts of potato psyllid, which vectors the disease.

Scientists at the Hermiston Agricultural Research and Extension Center advise growers and fieldmen to look for foliar symptoms of the disease as they scout fields, and treat with insecticides if warranted.

"It is extremely important not to allow colonization of the psyllids in the fields," wrote station superintendent Phil Hamm and extension entomologist Silvia Rondon in a university bulletin.

Potato plants infected with zebra chip have reddish foliage, thick nodes and dying vines.

The disease can render potatoes unmarketable by causing dark stripes in the flesh.

The center is asking growers to bring plants and tubers to the center for confirmation if growers suspect plants are infected.

Zebra chip was first recorded in Mexico in 1994 and first observed in the U.S. in Texas in 2000.

It was first reported in the Northwest late in the 2011 growing season.

The center also reports that psyllids from two locations -- one near Cold Springs Reservoir and the second at the experiment station -- tested positive for the Liberibacter bacterium that causes zebra chip.

Psyllids from 13 locations were tested.