Billbugs

If you think billbugs are damaging your client's lawn, you should take a look at the concrete surrounding the lawn. Billbugs can do some major damage to a lawn, and unless swarms of billbugs are witnessed walking across a driveway, their presence is difficult to detect. The best time to detect their presence is in the spring when the adults are moving from their overwintering sites – usually mulched landscapes or unmowed, adjacent fields – to the turf areas.
 

Identification: There are at least eight turfgrass damaging species of billbugs in North America, in addition to the bluegrass billbug. Two others – the hunting billbug – Sphenophorus venatus – and the "Denver" billbug – S. cicatristriatus.
 

Damage: The bluegrass billbug damages bluegrass and fescue lawns during the larval stage. Billbug larvae are not a true white grub. Nonetheless, they can do extensive damage by feeding on stems, crowns and shallow roots. The legless larvae are white, stubby and humpbacked, have a brown head, and are approximately 0.25-0.50 inch long when mature. The adult is a small, dark brown to black weevil approximately 0.25 inch long with a long curved snout and often are seen walking across concrete sidewalks and driveways adjacent to infested areas. Females lay their eggs in May in holes that they chew into stems and crown tissue.

After hatching, the larvae tunnel through the lower plant parts as they feed, and even may migrate down to shallow roots. Small patches of damaged or dead grass appear in midsummer and may coalesce into larger dead patches. If billbugs are suspected, look for hollowed stems and yellowish saw dust-like frass at the bases of plants. Dead turf pulls up easily because of the lack of root resistance. Larvae stop feeding in midsummer to tunnel into the soil to pupate into the adult stage.

If the weather is conducive, a second partial generation may occur that ranges from September to October. Adult weevils of the second generation overwinter under leaves that accumulate in shrubs, tall grass and against buildings.
 

Control: Generally, billbugs presence can be picked up sometime in April through May, and one of the best methods of detection is with a pitfall trap constructed of a 16-ounce plastic cup, and a 3-ounce collection cup. A cone-shaped cup is set into the 3-ounce collection cup, and both are then inserted into the 16-ounce cup. This entire assembly is set into a hole made in the turf that is made with a 4-inch golf course cup cutter, and situated with the rim of the cup slightly below soil level. The insects crawling across the turf fall into the trap and are unable to get out. Such a trap usually reveals quite a bit about what crawls across the grass: army worms, sod webworms, beetles, spiders and if present, the billbug adult – either the bluegrass or Denver species.

Like other insect problems, there is a recommended threshold to monitor for. If the number of billbugs collected exceeds seven, then the potential for serious turfgrass damage is at hand. Control with insecticides is not as effective as one would wish; instead work on improving the vigor of the turfgrass in the damaged areas with watering, fertilizing and reseeding. Insecticides are pretty much ineffective in penetrating thatch and reaching the billbug larvae feeding on the crowns and roots.

The cultural practices of mowing and collecting clippings, along with annual core aerations will go a long way in keeping the billbug population at acceptable levels.

The author is a horticulturist and turfgrass specialist at North Dakota State University.