Billbugs are pests belonging to the weevil family (Curculionidae) that primarily target turfgrass across North America. Common species include the Bluegrass and Hunting Billbugs. They are frequently misdiagnosed, as the widespread damage they cause to lawns is often incorrectly attributed to drought stress, disease, or other insect activity. Billbugs pose a serious threat to grass health, especially in areas featuring Kentucky bluegrass and zoysiagrass.
Physical Identification of Billbugs
The adult billbug is a small beetle, typically one-quarter to one-half inch long, with a hard, pitted exoskeleton that is usually black, gray, or dark brown. The most recognizable feature is the characteristic long, curved snout, or rostrum, which is a hallmark of the weevil family and houses the chewing mouthparts. Adults are generally slow-moving and are often observed walking along sidewalks and driveways, especially during the spring.
The larval stage, which causes the majority of turf damage, looks distinctly different. Larvae are creamy-white, legless grubs with a slightly curved body and a prominent yellowish-brown or reddish-brown head capsule. This absence of legs distinguishes them from other common lawn pests, such as white grubs. Fully developed larvae can reach up to 10 millimeters long before pupating.
The Billbug Life Cycle
Billbugs undergo a four-stage life cycle: egg, larva, pupa, and adult. Adults typically overwinter in sheltered areas like leaf litter, thatch, or soil crevices, becoming active in the spring when soil surface temperatures rise, often around 65°F. Females begin to lay their white, elongate eggs inside small holes they chew into the grass stems near the base.
Eggs hatch after one to two weeks, and the newly emerged larvae immediately begin to tunnel and feed internally within the grass stem. Once the larvae grow too large for the stem, they exit and move down to the soil. The larger larvae then feed externally on the plant’s crown and roots, causing the most visible turf destruction. Larval feeding usually peaks during the summer months, and the larvae eventually pupate in the soil before emerging as adults in late summer or early fall to seek overwintering sites.
Recognizing Billbug Damage
Damage from billbugs often appears as irregular, straw-colored or brown patches of turf, easily confused with drought stress or a fungal disease like Dollar Spot. The most telling symptom is that damaged grass plants pull up easily from the soil, often breaking off cleanly at the crown. This occurs because the larvae have severed the stems and roots just above the soil line.
A simple verification method is the “tug test.” If a section of dead or damaged turf is pulled upward and the grass stems break off easily, the exposed ends should be examined for frass. Frass is a fine, sawdust-like material (larval excrement) packed inside the hollowed-out stems, and its presence is a definitive sign of billbug activity. Damage is typically most visible from mid-June throughout the summer when the larvae are actively feeding.
Prevention and Control Strategies
Preventing billbug infestations involves a combination of cultural and chemical strategies, with timing being the most important factor for success. Cultural controls focus on promoting a robust and healthy turfgrass stand that can better tolerate minor feeding damage. This includes maintaining proper mowing heights, reducing excessive thatch where adults may hide, and ensuring adequate irrigation and nutrition without over-fertilizing.
For chemical control, timing an application to the life cycle is paramount, as the adults and the stem-boring larvae are difficult to target. Preventative control is highly effective and aims to eliminate adults before they lay eggs in the spring or target the young larvae within the grass stems. Systemic insecticides, such as neonicotinoids or anthranilic diamides, are absorbed by the plant and can be applied in the late spring to target the early larvae as they tunnel.
Targeting the overwintering adults as they become active in the spring, when the soil temperature reaches about 65°F, is another effective preventative approach. Curative treatments are only necessary once damage is already visible, and their goal is to prevent further destruction by controlling the larger, root-feeding larvae. Curative applications require watering the insecticide into the soil to reach the larvae feeding below the surface.