Billbugs have been reported as serious pests of lawns and other turf areas since the late 1800s. Today, we know of at least eight turfgrass-damaging species. The most important of which are the bluegrass billbug, Sphenophorus parvulus, the hunting billbug, S. veatus, and the “Denver” billbug, S. cicatristiatus. We will focus on the Bluegrass Billbug.
Descriptions and Life Histories
Billbug larvae (grubs) appear similar to white grubs but are legless. They have cream-colored bodies with brown heads, and when fully developed are about ¼ to ½ inch long, depending on the species. Their bodies are slightly curved and resemble a grain of puffed rice.
The bluegrass billbug was first reposted as a turf grass pest in Nebraska and Iowa in 1890. Today, this insect is recognized as a serious pest of Kentucky bluegrass nearly everywhere the grass is grown. Although preferring Kentucky bluegrass (as its name implies), the bluegrass billbug also feeds on perennial ryegrass, fescue, and timothy grass.
Adult bluegrass billbugs are typical weevils (or snout beetles) with mouthparts located at the end of a curved snout our bill. These insects, which are about ¼ inch long and dark brown to black, are slow moving and frequently “play possum” when disturbed. From April to June and again in September and October they can often be observed crawling on sidewalks and driveways near infested turf.
The greatest injury from billbugs usually occurs from mid-June through late July during the period of maximum heat and drought stress. Because billbug injury is easily mistaken for white grub damage, disease or even plant stress, the damaged turf area should be carefully examined to confirm the presence of billbugs before making a management decision. Knowledge of prior billbug infestations in a turf area will be useful in making a diagnosis.
Newly hatched billbug larvae tunnel in grass stems, hollowing out the stem and leaving fine sawdust-like plant debris and excrement. Infested stems discolor and when pulled, readily break away at or near the crown. Subsurface feeding by older larvae can completely destroy the plant’s root system, causing the turf to appear drought stressed.
Under heavy billbug pressure the turfgrass will eventually turn brown and die. Adult billbugs also feed on grass stems and blades but cause only minor injury to the turf. Billbug damage rarely occurs in turf strands less than three years old.
Billbug adults are difficult to detect, even when numerous. The best time to begin monitoring is when adults are moving from overwintering sites back into turf areas. Look for bluegrass adults on sidewalks and driveways from April through May. Adults can be flushed from the turf by mixing 1 tablespoon of 1 percent pyrethrins or 1/ 4 cup of lemon-scented household detergent with 2 gallons of water and applying it over one square yard of surface area. These drenches irritate the billbugs and drive them to the surface in about 15 minutes where they can be counted.
Billbug larvae can be detected by selecting several locations in the turf area and peeling back ¼ square foot (6”x6”) of turf to a depth of 2 to 3 inches at each site. Turfgrass managers with access to a golf course cup cutter can take 4-inch (0.1 square foot) turf-soil core samples.
Effective cultural practices can significantly reduce billbug damage. Selection of adapted turfgrass cultivars and proper fertilization and irrigation programs will minimize the impact of billbug infestations. In additional, certain Kentucky bluegrass cultivars have natural resistance to billbugs, and several endophyte-enhanced, billbug-resistant cultivars of perennial ryegrass, tall and fine leaf fescues are now available. These have proven very effective in reducing billbug damage.
The most reliable strategy for managing an established billbug infestation involves insecticide applications in late April through mid-May to reduce the number of overwintered adults before they can deposit their eggs. Experience has shown that an insecticide application is usually justified when visual observation or irritant flushes confirm the presences of one adult billbug per square foot of turf. If warranted, apply insecticides to newly mowed turfgrass (collect and remove clippings) and irrigate lightly after application to wash the insecticide off grass blades onto the soil surface where billbug adults are found.
Where pitfall traps are used two to five adult bluegrass billbugs captures per trap during the trapping period indicates the potential for light to moderate damage. If trap catches exceed seven to ten billbugs per trap, severe turfgrass injury is probably. Insecticidal control of billbug larvae is difficult. Insecticides will not enter stems and may not penetrate the thatch layer to reach larvae feeding in the plant crown and root zone. During this period, it may be better to water and fertilize damaged turf areas to stimulate new growth rather than to attempt control. However, if larvae exceed 25 to 30 per square foot of turf, control is probably warranted.
Before application, turf should be well-watered to moisten the soil and enhance insecticide penetration. Immediately after treatment, heavy watering (1/2 to 1 inch) is needed to facilitate movement of the insecticide into the feeding zone. Aerification with irrigation may enhance larval control.
F. P. Baxendale. (1997). Insects and Related Pests of Turfgrass. In F. Baxendale, Ph.D., & R. Gaussoin, Ph.D., Integrated Turfgrass Management for the Northern Great Plains (pp. 51-56). Location: Nebraska