Bluegrass billbug is a very difficult insect to diagnose in turf. Billbug damage is often confused with compacted turf, drought stress, nematode damage, white grubs, and dollar spot. As a result of this confusion, billbugs are often not diagnosed and can become a bigger problem the longer they stay untreated. The damage becomes apparent by mid-June as individual plants begin to decline from crown feeding by the larvae.
What is a Billbug?
Billbugs are in the weevil family of insects, and there are at least 4 types that infest turf in the Midwest region. The bluegrass billbug is the most common. It prefers Kentucky bluegrass but will infest fine fescue, tall fescue and perennial ryegrass as well. All billbug species can be identified by the snout that protrudes from the head. The adult insects are roughly 7-8 mm long. The larvae are legless and have a humped back. The grubs inhabit the soil and the adult beetles are found in the crowns of the grass plant. The grubs are a cream color and the adults have a chestnut colored head with puncture marks that look like striping on their bodies.
How Do Billbugs Cause Damage?
Adults overwinter in the thatch layer, and also in cracks and crevices in soil and around sidewalks and driveways and buildings. They become active in April/May when surface soil temps reach 65 degrees. The beetles feed on grass stems, chewing small holes which do not damage turf plant. The females insert eggs into these holes, and the eggs hatch into larvae that bore into the grass stems until they deplete the plant juices. By June, the larger larvae begin to feed on the crowns of the grass plant, which can cause significant injury and even plant death. Billbugs pupate in July and about six weeks later, new adults emerge and begin feeding.
How Can I Tell If My Lawn Has Billbug Damage?
Here is what we look for: The early phase of damage appears as 2-3 inch dead spots enlarging as damage proceeds. To examine areas for billbugs, we pull the crowns of the grass plant apart. If stems easily dislodge or snap off, the base of the blades should be examined for sawdust-like frass (bug poop), a sign of larvae feeding. This inspection method is known as the “tug” test. The beetles also seem to like warm concrete so you may see them on the sidewalk.
What is the Treatment for Billbug Damage?
Many insecticides are effective against billbugs. We typically use Arena or Talstar/Avalon insecticides. These products need to be watered in after application for maximum effectiveness. Most turf recovers quickly from this pest if it is being cared for properly.