Bluegrass Billbugs In Iowa

The map shows the predicted date of first adult emergence of bluegrass billbug in Iowa, based on actual temperatures recorded this spring. Bluegrass billbug is recognized as an occasional pest of Kentucky bluegrass. Although it prefers Kentucky bluegrass (as its name implies), the bluegrass billbug also feeds on perennial ryegrass, fescue, and timothy.

Adult bluegrass billbugs are weevils, or snout beetles, with mouthparts located at the end of a curved snout or bill. Adults are about 1/2 inch long and dark brown to black, and are slow moving and frequently play possum when disturbed. They are often seen crawling on sidewalks and driveways near infested turf. After mating in the spring, females deposit their eggs in cavities chewed into plant stems near the crown. Newly hatched larvae are small and C-shaped, and feed for 2 to 3 weeks within stems before moving to the grass crowns and roots. There they continue to feed on roots and underground stems. Billbug larvae usually feed just below the thatch layer, but occasionally feed as much as 2 to 3 inches underground. Heaviest damage occurs in late June and early July, with pupation at the base of the thatch by mid-July. Billbug injury is easily mistaken for white grub or sod webworm damage, disease, or even plant stress, so the damaged turf area should be carefully examined to confirm the presence of billbugs before applying any treatments. Turf that has a history of billbug damage is likely to suffer repeat damage, and billbug damage rarely occurs in turf stands less than 3 years old.

Billbug adults are difficult to scout for because they are small and blend into their environment. They can be spotted on driveways and sidewalks from April through May. Pitfall traps ( http://entomology.unl.edu/turfent/turfchts/pitfall.jpg ) can be placed in turfgrass areas at 20-foot intervals where billbugs are suspected. These traps should be monitored two times a week until the first of June. Billbug adults can also be "flushed" from a turfgrass area by mixing 1/4 cup of lemon-scented dish detergent with 2 gallons of water. This mixture is applied as a drench over the turfgrass surface; if any billbug adults are present, they will come to the surface within 15 minutes.

Management of bluegrass billbug generally involves a properly timed insecticide treatment for the adult stage. According to the University of Nebraska research, one billbug adult from irritant soap flushes or 2 5 adults per pitfall trap justifies the use of an insecticide. With the loss of many homeowner turfgrass insecticides, check with your retail outlet for available products. Preventive applications should be made during late April or early May.

Long-term billbug management should include use of resistant turfgrass varieties. Ohio State University lists 'Park', 'Arista', 'NuDwarf', 'Delta', 'Kenblue', and 'South Dakota certified' as resistant or tolerant Kentucky bluegrass varieties. Many perennial ryegrasses and fescues have endophytes enabling the grass to be resistant to billbugs. If you are renovating a lawn after billbug damage, use a blend of turfgrasses known to be resistant to this pest.

This article originally appeared in the 5/2/2003 issue.

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