The Washington Department of Agriculture plans to aerial spray 220 acres in southwest Washington next spring to squelch a gypsy moth outbreak.
WSDA snared 16 European gypsy moths last summer near Yacolt, about 20 miles northeast of Clark County. In the fall, WSDA moth hunters found a spent egg mass and then a fresh egg mass capable of producing 1,000 gypsy moths.
WSDA consulted with the U.S. Department of Agriculture and entomologists from other states before deciding to spray.
“It was an obvious decision. There wasn’t anyone who questioned whether we should,” WSDA’s pest program manager, Jim Marra, said.
WSDA decided against spraying in Seattle, where 8 moths were trapped, including 6 in the Capital Hill neighborhood. A search didn’t turn up more evidence of a developing gypsy moth population, Marra said.
Gypsy moths are established in all or parts of 19 states and the District of Columbia, according to USDA. The state farthest west is Wisconsin.
Western states have been battling to keep the leaf-eating pest from advancing. Since 1979, WSDA has conducted 90 eradication treatments. Most recently, the department in 2013 sprayed about 180 acres in the neighboring King County cities of Tukwila and Renton.
In Yacolt, WSDA plans to spray three times in April and May as waves of caterpillars emerge. The department will spray Bacillius thuringienses kurstaki, a biological pesticide sold as Foray and commonly used in organic agriculture, according to WSDA.
The sparsely populated area won’t be evacuated, but residents will be advised to stay indoors for a half hour after spraying as a precaution, Marra said.
The department opted for aerial spraying because much of the rugged terrain is hard to reach on the ground, he said.
WSDA will host an open house in February in Yacolt to inform residents about the spraying. The time and place have not been set.
WSDA will review its proposal to comply with the State Environmental Policy Act and National Environmental Policy Act before formally deciding whether to spay.
Gypsy moth egg masses travel across the United States attached to personal property, such as outdoor furniture and birdhouses.
Marra said WSDA was unable to pinpoint how gypsy moths got to Yacolt.
In all, WSDA trapped 27 gypsy moths in five counties this year.