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Billbugs are gray, black to reddish-brown weevils, each of which has a characteristic, conspicuous snout with chewing mouthparts at the tip. Though over 60 species exist, only four are known to cause damage to turfgrasses in North America. The bluegrass billbug damages most cool-season grasses (especially Kentucky bluegrass and perennial ryegrass) from Washington to Utah to the East Coast of the United States. The hunting billbug occurs in the warm-season turf zone and damages bermudagrass and zoysiagrass. The larvae of these two species account for most of the damage done by billbugs.
The Phoenician (=Phoenix) billbug is a pest of bermudagrass and zoysiagrass in Southern California. The Denver (=Rocky Mountain) billbug is found in Kentucky bluegrass and perennial ryegrass from New Mexico through Colorado and into Utah and Washington.
DAMAGE, DIAGNOSIS & MONITORING. Billbug damage is similar to that caused by drought, disease and other insects. Careful examination (hands and knees) of damaged turf is the key to correct diagnosis.
Adult billbugs feed on grass stems and stolons, occasionally chewing transverse holes through them. Damage inflicted by this feeding is considered insignificant. Some species lay eggs in the feeding holes and others chew slits in stems and stolons and insert eggs in them.
The wandering nature of billbug adults is a good indicator of a potential problem in nearby turf. Careful observation for adults on sidewalks, driveways and along gutters during migration times should provide warning of a possible infestation of larvae. When picked up or disturbed, adults fold their legs tight against the body and appear dead.
A good method of monitoring adult activity is to place small plastic cups (pit fall traps) inside holes made by using a 4¼-inch cup cutter. Traps can be placed along the turf margins near flowerbeds so that they are out of the way. Adults falling into the traps can be easily counted by inspecting the traps 2 to 3 times a week.
Billbug larvae are white and legless soil, crown and root inhabitants, 3/8-inch long with a tan to brown head. They are fat with the tail end somewhat larger than the head end. Larvae feed on turfgrass roots, stolons, stems and crowns, often cutting the stems off at the crown. If small patches of turf appear to be dying, the best way to determine if billbugs are responsible is by carefully examining the damaged turf. Turf damaged by larvae is easily pulled out by hand with the stems breaking off at the crown. A good indicator is the presence of fine, sawdust-like material (frass) left by larvae feeding in the crown or root zone. Look for evidence of larval feeding in the crown, at the base of the stem and use a knife to probe among the roots for larvae.
LIFE CYCLES & HABITS. Except for the hunting billbug, all billbugs appear to have a single generation per year. The hunting billbug may breed continuously in southern states. Most billbugs spend the winter as adults, though significant numbers of hunting and Denver billbugs overwinter as larvae. For most billbugs, a spring adult feeding period is followed by egg laying, and larvae developing over the summer.
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