A pesticide will be sprayed from the air over 1,700 acres in Western Washington next spring to kill gypsy moth caterpillars, according to a plan announced Dec. 19 by the state Department of Agriculture.
The department plans to spray 699 acres at Martha Lake in Snohomish County, 270 acres on Union Hill-Novelty Hill in King County and 299 acres in Gilberton and 438 acres in Crosby in Kitsap County.
European gypsy moths were trapped last summer for the third year in a year in Gilberton and Crosby, and for the second straight year in Union Hill-Novelty Hill, east of Redmond.
The spraying at Martha Lake, just east of Interstate 5 and north of Seattle, was motivated by the capture of a single Asian gypsy moth.
Asian gypsy moths are potentially more dangerous. They feed more readily on evergreen trees and have a greater range. Female Asian gypsy moths can fly, while female European gypsy moths are flightless. Before this summer, an Asian gypsy moth had not been found in Washington since 2015.
“It’s the standard response to Asian gypsy moths — to spray for even one,” department spokeswoman Karla Salp said.
If the department needed another reason, the capture of a European gypsy moth nearby provided one. Salp said the department is concerned about cross-breeding between the Asian and European strains. The department in 2016 found one gypsy moth that had cross-bred, she said.
Gypsy moth caterpillars feed on hundreds of trees and shrubs, including Christmas trees and nursery plants. They lay eggs on hard surfaces, including personal belongings that are unwittingly transported across the country.
Gypsy moths are established in many Eastern and Midwest states, but have not settled in the West. Gypsy moths were first detected in Washington in 1974. Since then, the agriculture department has trapped for moths in the summer to detect outbreaks and sprayed in the spring as caterpillars emerge.
In all, the department this year snared the one Asian gypsy moth and 51 European gypsy moths in 10 counties, all west of the Cascades.
The spraying will occur over populated and forested areas. The department said it will host open houses in the areas to answer questions from the public.
The department expects to spend $620,000 on the operation. The state will get three-quarters of the money from the USDA.
The department trapped nine European gypsy moths in Gilberton, six on Union Hill-Novelty Hill and four in Crosby.
The department captured eight gypsy months on Orcas Island in San Juan County, but did not catch any there last year. Salp said the department will put more traps than usual on the island next summer.
As in the past, the department will spray Bacillius thuringiensis var. kurstaki, or Btk, a naturally occurring bacteria. The pesticide was developed in the 1960s and 1970s to spray over forests and has not been harmful to plants, pets or humans, according to the USDA.