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Hopper infestations cause concern

Grasshopper numbers highest in nearly 20 years


Capital Press

HERMISTON, Ore. -- Before this year, Oregon State University Extension entomologist Silvia Rondon had never seen more than an isolated grasshopper in her sticky traps at the Hermiston Research and Extension Center.

"Now they are in big numbers," Rondon said. "This is the first time in years we are in the red zone."

The Hermiston area this year is joining Union, Baker and Klamath counties as hot spots in what is fast becoming a heavy grasshopper infestation.

Preliminary results from Oregon Department of Agriculture surveys show the infestation is higher than even last year, when nearly 2 million acres -- about 12 percent of Oregon's agricultural land -- were infested.

"The acreage may be a little higher, but the densities are much higher that last year," ODA entomologist Paul Blom said.

Blom, who works at La Grande in Union County, said landowners tell him grasshopper populations haven't been this high since the early 1990s.

"We're finding 200 to 300 grasshoppers in a square yard, and hundreds of thousands in a small area," ODA entomologist Helmuth Rogg said.

The main culprit is the clearwinged grasshopper, one of about 80 grasshopper species in the state, Rogg said.

Grasshoppers annually attack 20 to 25 percent of rangeland in 17 Western states and cause an estimated $400 million in forage losses, according to the USDA.

When rangelands go dry, grasshoppers move into food crops, Blom said.

"They have some food preferences, but by and large, they'll eat almost anything that is green and succulent," Blom said.

Young grasshoppers are the most voracious feeders, Blom said. But adults also feed on forage and food crops.

ODA is nearing completion of its nymph surveys, which are designed to help the state and federal officials and landowners understand how many grasshoppers are present.

Next the department will conduct its adult survey, which will provide an early peek at population levels expected next year.

Blom said that as of July 22, technicians are finding mostly nymphs and only a few adults.

Usually at this time of year, grasshoppers have completed their development and only adults are present, Rogg said.

The late hatching is good news for growers and ranchers still looking to treat for the pest. Grasshoppers are best controlled in their nymphal stages, Blom said.

"That's when you can control them with the least amount of environmental impact," Blom said. "It is also when they are most aggregated."

Dimilin, an insect growth regulator, is the most commonly used insecticide on the nymphal stages of grasshoppers. Once grasshoppers reach the adult stage, carbaryl and malathion are the insecticides most widely used.


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