A Skagit County farm was hit last week with an infestation of a pest uncommon in the Pacific Northwest that has the potential to seriously damage corn crops, according to an entomologist with the Washington State University Skagit County Extension. 

Charles Coslor, the extension's entomology coordinator, said western corn rootworm, a species of beetle, was found in corn fields in the Sedro-Woolley area and eradicated with a pesticide applied by helicopter. 

"Large infestations can be very serious," he said in an email. "They can cause corn ears to terminate. This infestation was apparently bad enough to require an immediate aerial pesticide application."

Coslor said the quick pesticide application was critical because it killed the pest before it could lay eggs. 

The outbreak appears to be isolated. Coslor said he has not confirmed any other reports of the pest in Skagit County. 

He said the bug is actually in the beetle family, but known by its common name western corn rootworm. 

"A lot of corn is grown in Skagit County, but western corn rootworm is not a common pest here," he said in an email. "It is widespread east of the Rockies, especially in the Corn Belt states."

A research article in a 2014 Pacific Northwest Extension publication describes the bug as "a notorious pest of corn in much of the continental United States ... This insect has consistently damaged corn in the U.S. for over a century ... becoming known as the 'billion-dollar pest.'"

Coslor said outbreaks in the Pacific Northwest are sporadic and isolated. A large outbreak affected Whatcom County farms several years ago.

He said because Skagit County farmers grow a large variety of crops, the pest is not able to take off. The species goes after only corn. 

Coslor said he suspects hot weather and drought conditions have created "favorable conditions" for the beetle this year.

"Insects are cold-blooded and need warm weather to function properly," he said. "The warmer it is, the faster they can grow."

In addition, drought-stressed crops are more vulnerable to insect damage, he said. 

The beetles lay eggs in the soil and die in the fall, Coslor said. In the spring when the eggs hatch, the larvae feed on roots underground, which can cause rot and disease in corn stalks and even kill them, he said. In the summer, they reach adulthood and become black and yellow beetles.

The beetles spend a couple weeks feeding on the corn before laying eggs again, he said.

Rotating a field with noncorn crops is the most effective way to prevent infestations because it deprives the beetle of its food source, the 2014 article in the Pacific Northwest Extension publication states.

Coslor said the corn from the affected field near Sedro-Woolley will be processed into silage for animal feed, not sold as fresh, sweet corn. He thinks the crop is salvageable. 

He said though pesticide applications by helicopter can be an alarming sight, they have been increasing in Skagit County since 2010 following the introduction of an invasive insect that attacks berries. 

— Reporter Jacqueline Allison: jallison@skagitpublishing.com, 360-416-2145, Twitter: @Jacqueline_SVH

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