Billbugs are a problem in eastern Washington. They have not yet been detected in western Washington. Both the adults and larvae cause damage. Kentucky bluegrass is severely damaged, while bentgrass is not affected. Adult billbugs are dull gray or shiny black weevils with long, distinctive snouts. They are 1/4"-1/2" long and cause minor damage by feeding on grass stems. The larvae are legless white grubs with brown heads. They are about 1/4" at maturity. The larvae initially feed on the stems, then later move to the crown region and roots, cutting roots off just below ground. Aboveground, damaged grass appears dry and brown in irregular patches. The damaged sod is easily lifted away from the soil, exposing the grubs. Overwintering adults lay eggs from May to July.

Management Options

Non-Chemical Management

Several natural enemies help control billbug populations, including a fungal disease.
Grasses containing an alkaloid-producing endophytic fungus (endophyte) are resistant to billbugs.

Select non-chemical management options as your first choice!

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides

Treat the entire lawn when this insect is seen. Spring applications when adults first become active may prevent buildup of larval populations. Mow or remove weed flowers before applying to lawn.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.

Safer Brand BioNEEM Multi-Purpose Insecticide & Repellent Conc [Organic]
Active ingredient: azadirachtin | EPA reg no: 70051-6-42697
This list may not include all products registered for this use.

Images

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Caption: Billbug Photo by: K. Grey
Caption: Billbug damage Photo by: A.L. Antonelli
Caption: Billbug damage close-up Photo by: A.L. Antonelli
Caption: Billbug larvae Photo by: A.L. Antonelli

WSU Extension

Hortsense