Sphenophorus Parvulus

Adult bluegrass billbugs are a small dark gray to black weevil approximately 5/16 of an inch long (Images A & B). Individuals are typically found in small numbers in most lawns. They have a single generation per year with adults becoming active in May. Eggs are deposited inside small holes chewed into the grass stem between late May and early July. Eggs hatch in about 6 days and the larvae feed inside the stems. It is the larval stage that causes the damage. Larvae pupate and adults emerge in August. They find places to hide in the turf and overwinter as adults.

Notes: Damage from this pest is uncommon because of predators and diseases. Regular applications of a synthetic pyrethroid insecticides (such as deltamethrin, cyfluthrin, bifenthrin and lambda-cyhalothrin) after early June have been known to suppress natural enemies and allow billbugs to increase to damaging populations.

  • Crops Affected: turf


    Distant: Lawn turns brown in patches in late July. Damage is sometimes more severe next to sidewalks, driveways and around trees (Images C & D).

    Up close: In a "tug test" infested stems tend to break at the crown. Broken-off stems are filled with fine, whitish sawdust. Billbug larvae can be found in stem or in soil around roots in July.

    Description of damaging stage: Small, legless, white larvae with a brown head capsule. They can be 1/2 of an inch long when full grown (Image E). The larvae will start feeding inside the stems. When they become larger, they will move out of the stems and feed on the roots and crowns of the grass. When there are enough present to cause damage, they leave a fairly obvious amount of sawdust-like excrement (called frass) where they are feeding.

    Host: Kentucky bluegrass, perennial ryegrass, fine fescue.

    Site: Most common in non-irrigated home lawns with some Kentucky bluegrass.


    Sampling: Hands and knees - Look at the edges of dead patches to find damaged grass stems and stems filled with frass. Look in the soil around the crown and roots for the larvae.

    Managing Billbugs: If damage and larvae are observed, it may be too late to do anything in that calendar year. Avoid any applications of synthetic pyrethroid insecticides such as deltamethrin, cyfluthrin, bifenthrin, permethrin and lambda-cyhalothrin for the rest of the current year and the next year against other insect problems as these will kill natural enemies of billbugs and will contribute to billbug population increases. Apply clothianidin or another neonicotinoid insecticide (such as clothianidin, imidacloprid or thiamethoxam) in late May of the year following the damage.

    Preventing Pest Injury to Turfgrass: Home lawns, recreational turf and golf course roughs can be managed to avoid insect injury without insecticides by using proper fertility, mowing at a height of 3.0 to 4.0 inches, and watering during dry periods. This will build a dense stand of turf and a diverse community of insects that will keep turf pests under control. All lawns in Michigan will typically start off lush and green in the spring and will go dormant and turn brown during periods of little rain. Information on the use of insecticides to treat turf pest problems is only meant to be used for the unusual cases where turf damage from pests becomes unacceptable. Even then, insecticides should only be used in areas of a lawn with severe turf damage, and only until a dense turf is re-established.

    Using insecticides: Use insecticides judiciously, temporarily, and only in response to unacceptable turf injury. Many insecticides are poisonous if ingested, and therefore must be stored in places where they cannot be found by children. Use the rate recommended on the label for the pest you are attempting to control. Wear rubber gloves, safety glasses (or goggles), rubber boots, long pants and long sleeved shirts when mixing and applying insecticides. The most caution is needed when mixing a concentrated insecticide in water, because skin contact with the concentrated insecticide in the original container is more dangerous than contact with the diluted insecticide after mixing. Water the turf immediately after applying the insecticide to wash it to the base of the plants or into the soil and allow the turf to dry before allowing access by people and pets.