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Washington takes aim at Spartina, spongy moth

Moth sprays began May 10; Spartina treatments to begin June 1.

Farm Press Staff

May 20, 2024

5 Min Read
Gypsy moth caterpillar
Gypsy moth caterpillar.USDA ARS

Washington’s State Department of Agriculture is ramping up treatments against two invasive species – the spongy moth and the aggressive Spartina weed.

Spongy moth

A low-flying airplane began treatments to eradicate spongy moth caterpillars on May 10, with plans to aerially treat about 1400 acres in Thurston County and 900 acres in Skagit County with a naturally occurring soil bacteria, Btk (Bacillus thuringiensis var. kurstaki). Because the Skagit County site is in a cooler climate, treatments were anticipated to start there mid- to late-May.

The sites will each be treated three times, with applications approximately 3 – 10 days apart. All treatments are weather dependent and the schedule is subject to change. WSDA expects to complete all applications by early June.

Because weather conditions heavily influence when treatments occur, WSDA advises people in or near the treatment areas to visit agr.wa.gov/moths to sign up for e-mail, text or robo-call alerts that are issued the day before applications are scheduled to take place. Changes in scheduled treatments will also be shared through these notification systems. WSDA also mailed multiple postcards to residents in and near the treatment areas advising them of the upcoming treatments. The public can enter an address in a map on the agency website to determine whether their residence is within or near the treatment area.

According to the Washington State Department of Health, Btk poses very low risk to humans, pets, birds, fish and bees. Btk is found naturally in the environment and has an excellent safety record while also being effective for spongy moth eradication. Although the risk to humans is low, as a precaution, DOH recommends that people who wish to minimize their exposure to the spray remain indoors with doors and windows closed during spraying and for 30 minutes afterward. Let the spray dry before allowing children to play outside, wash with soap and water if you do have skin contact with the spray, and rinse your eyes with water if eye contact occurs.

Btk is sticky. Residents in the treatment areas may choose to cover cars parked outside and bring in toys, etc. to protect them from the spray. However, Btk can be cleaned off outdoor articles with soap and water.

This is the 50th year of the spongy moth program at WSDA. It has been one of the most successful pest detection and eradication programs in the country, preventing spongy moths from establishing in the state and protecting our environment, communities and agriculture from this destructive, invasive pest. The program has trapped for spongy moths (known as gypsy moths when the program started) since 1974 and conducted the first eradication program in 1979. The WSDA Pest Program has safely eradicated every spongy moth population attempting to establish in the state since the program began.

Spongy moths pose a serious threat to Washington’s environment, with the caterpillars feeding on over 300 types of trees, plants and shrubs. The pest is permanently established in 20 states across the Northeast and Midwest, where it has defoliated millions of acres of forest and urban trees. In 2017, spongy moth caterpillars defoliated one-third of the entire state of Massachusetts and in 2018, they lost about one-quarter of their hardwood trees, including three-quarters of their oak trees, in large part due to spongy moth infestations.

If spongy moth were to become established in Washington, it would threaten forest ecosystems, defoliate or kill trees and shrubs in backyards and parks, lead to quarantine restrictions on forest products and horticulture, and result in long-term increased homeowner pesticide use.

Visit the agency’s spongy moth web page at agr.wa.gov/moths to learn more or contact the WSDA Pest Program at [email protected] or 1-800-443-6684.


This year’s treatment season for Spartina, an aggressive invasive weed, starts June 1 and will continue through November.

Eradication efforts will take place in multiple areas, including Grays Harbor, Hood Canal, Willapa Bay, Puget Sound, the north and west sides of the Olympic Peninsula and near the mouth of the Columbia River.

This year’s efforts build on the work completed last season when thorough surveys detected recently established Spartina within restored wetlands in the North Puget Sound. The project partners will work to stop the trend of Spartina spreading into and impacting important restoration projects. Since 1995, WSDA has served as the lead state agency for Spartina eradication, facilitating the cooperation of local, state, federal and tribal governments; universities; interested groups; and private landowners. The cooperative effort located and treated over 17,000 individual Spartina plants last year.

The Spartina eradication effort has been highly effective – reducing infestations from a high of more than 9,000 solid acres in 2003 to just over four total acres in 2023.

The effort has successfully eradicated Spartina at 75 sites, however significant work remains to be done. The four remaining acres are spread over 126 sites - meaning 62 percent of Washington’s known infestations are not yet eradicated.

“Our goal is to eradicate Washington’s remaining Spartina infestations, protecting important habitat for salmon, waterfowl and shellfish,” said Chad Phillips, WSDA’s Spartina Program Coordinator. “The Spartina Eradication Program protects our state’s most productive estuaries and shoreline habitats. This year, with our project cooperators, we will continue the challenging work of finding and removing the thousands of Spartina plants that remain in the Puget Sound and along Washington’s coast.”

This season, project partners will survey thousands of acres of saltwater estuaries and hundreds of miles of shoreline. WSDA and its partners typically dig out small infestations by hand and utilize herbicides at larger sites.

Spartina, commonly known as cordgrass, can disrupt the ecosystems of native saltwater estuaries. If left unchecked, Spartina outcompetes native vegetation and converts ecologically healthy mudflats and estuaries into solid Spartina meadows. As a result, important habitat for salmon, forage fish, invertebrates, shorebirds and waterfowl are lost, the threat of flooding is increased, and the state’s shellfish industry is negatively impacted.

Visit agr.wa.gov to for more information on Spartina control efforts.

Source: Washington State Department of Agriculture

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