Some fields lost 50 percent of crop to zebra chip woes


Capital Press

HERMISTON, Ore. -- The 38th annual Hermiston Farm Fair and Trade Show may have been the largest ever, according to organizers.

Vendor slots filled fast, said Annette Teraberry, who books vendors.

Participation was at a record level, according to Don Horneck, an Oregon State University Extension agent who helps organize the event.

"It very well could be the biggest crowd ever," Horneck said the morning of Nov. 30. "I would guess there are between 300 and 400 people in the building right now."

The draw, he said, is zebra chip.

"Any time you have a new disease or a new pest in potatoes, interest is piqued and we have larger audiences," Horneck said.

Zebra chip, a plant disease vectored by potato psyllids, struck the Columbia Basin for the first time last summer. The disease causes unsightly black lines in potato chips, rendering them unmarketable. Foliar symptoms include chlorosis or leaf scorching.

Psyllids long have migrated to the Northwest from the Southwest, OSU plant pathologist Phil Hamm said. But last year they arrived earlier than usual and, for the first time, they carried the liberibacter bacteria that causes zebra chip.

Psyllids showed up in the Northwest in mid-June last year, Hamm said, about one month earlier than normal.

Scientists speculate that dry conditions in the Southwest drove the insects to the Northwest earlier.

Regionally, growers spent an additional $1 million or more on insecticide treatments last summer to slow the disease, Hamm estimated.

Some fields sustained heavy crop losses.

"Six to eight fields had substantial damage of 25 to 50 percent losses," Hamm said.

Ironically, damage in those fields was exacerbated because of low insect pressure, he said.

Normally, Hamm said, growers would have treated fields with insecticides and inadvertently controlled psyllids. Because last year was a low insect year, many growers scaled back treatment programs.

Because zebra chip had never been a problem here, growers weren't looking for it, he said, and it snuck up on them.

In Texas, where zebra chip has been present for more than 10 years, it is a top priority among growers, Hamm said.

Don Henne, a Texas A&M University research scientist who spoke at the farm fair, said growers in Texas sustained significant losses to the disease in the mid-2000s before shifting treatment programs.

Growers in recent years have moved away from contact insecticides, such as pyrethroids and organophosphates, to insecticides with systemic or translaminar activity, he said.

The systemic materials, which are taken up by the plants, are more effective, Henne said, primarily because psyllids tend to reside on the underside of leaves, where contact materials often don't reach.

Translaminar insecticides are absorbed by the plant's leaves.

Potato growers in Texas now routinely spray for psyllids every seven to 10 days from shortly after plant emergence until well into the growing season, he said.

A key to controlling psyllid, he said, is knocking back adult and nymph populations early in a season to deter feeding and prevent egg lay.

"Knowing the biology of the insect and monitoring them are keys to managing them," Henne said.

Psyllids that carry the liberibacter bacteria tend to spread it to multiple plants because of their tendency to hop from plant to plant and feed a little on each, Henne said.

Henne and other scientists couldn't say if the disease will be an ongoing problem in the Northwest.

Jim Crosslin, a USDA research plant pathologist based in Prosser, Wash., said that judging from the damage the disease has inflicted in Texas, the disease poses a significant threat to potato production in the Columbia Basin.

"Theoretically, this disease could annihilate the industry," he said. "We saw fields in Texas that were absolutely, 100 percent losses."

In fields where it is controlled, disease treatment costs have soared, Crosslin said. One grower this year spent an average of $400 an acre just on zebra chip control, he said.

Hamm said OSU scientists are developing control guidelines for growers. Guidelines will include some type of monitoring and treatment program recommendations, he said.

Scientists are unsure if psyllids can overwinter in the cold climate of the basin, but most doubt it. Henne said he has documented nymphs surviving at temperatures as low as 5 degrees Fahrenheit for 24 hours and adults at temperatures as low as 15 degrees.

But Henne speculated that freezes that kill host plants should remove the insect's food source. Still, he said, psyllids have a wide host range so could survive on winter wheat or other plants during the winter.

"There is a lot we don't know about their alternate host uses," he said.

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