Pest of the Month: Billbugs

By Nate Royalty, Ph.D.,

What does it look like?

Billbugs are weevils or “snout beetles.” Adults are typically 1/4 to 1/2 inch long and are gray or bluish-black in color. The adults may be brownish-red if coated with soil. They have a long, beaklike snout with prominent antennae near the tip. Billbug larvae are legless and white with brown heads.

Host material and range

Billbug species can be divided into two general groups — species that overwinter as adults and/or larvae and usually attack warm-season or transition turf, and species that overwinter as adults and attack cool-season turf.

Most published information on billbug biology is based on the bluegrass billbug (Sphenophorus parvulus). This species, the most common cool-season billbug pest in North America, infests Kentucky bluegrass, perennial ryegrass and fine or tall fescues. Adult females chew a hole in the stems of turf plants and deposit their eggs inside. The young larvae feed by tunneling inside of the host plant’s stem. Large larvae emerge from the stem and feed on the crown and roots of the plant. The bluegrass billbug is most commonly a pest in the northern United States, but it can also be found in cool-season turf in the southern states.

Less is known about the billbug complexes that attack warm-season turf. The most commonly occurring of these billbugs is the hunting billbug (S. venatus vestitus). Hunting billbug problems are becoming increasingly prevalent in the southeast, but the pest has been detected as far north as New Jersey. Research to date on hunting billbug suggests that there are two generations per year in the mid-Atlantic states, and up to six generations per year in Florida. Adults are most prevalent in the spring and fall, where their feeding near the soil surface damages zoysia and bermudagrass. Current research at North Carolina State University (supported by Bayer Environmental Science) and at the University of Florida will eventually enable lawn care operators to understand and manage this increasingly important pest.

Current threat

Billbug damage can be difficult to identify, since symptoms are similar to those of dollar spot and summer drought. Turf damaged by bluegrass billbug wilts, and billbug damage often forms small, circular whitish spots on heavily infested turf. Severe injury is most common in new lawns, especially those established with sod. Individual plants damaged by bluegrass billbug can easily be pulled out of the soil.

Hunting billbug damage is usually characterized by delayed greenup of warm-season grasses in the spring, or by dry patches in summer that do not recover when watered. Unlike white grub or mole cricket damage, infested soil usually remains firm even when plant roots are destroyed.

Prevention tips

Good cultural control practices, including aeration, irrigation and proper fertilization, will help prevent billbug infestation. It is important to remove thatch build-up regularly, as the insects often live and burrow in areas of thick thatch.

If a lawn must be renovated due to bluegrass billbug damage, a resistant, endophyte-containing ryegrass or fescue is recommended.

Treatment tips

Adult billbugs have a hard, armorlike exterior that does not easily absorb insecticides. Larvae are also difficult to kill because they spend the majority of their lives inside of the plant stems. As a result, effective billbug control requires a precise understanding of the insect’s biology and proper application technique.

Early applications of surface or thatch-targeted insecticides are effective in controlling bluegrass billbug adults before they oviposit. Studies at Ohio State University have found that products such as Merit insecticide are effective in controlling young larvae in the plants when applied in late April to late-May.

Less is known about the best application timing for control of hunting billbug, or for situations where multispecies billbug complexes attack turf. Additional research is necessary to determine the most cost-effective methods of managing these difficult billbug problems.


What can you do?

Diagnosing a bluegrass billbug infestation is very simple. Use the “tug test” — by pulling on several affected stems and tug them from the soil. Turf damaged by billbugs will easily break off, revealing piles of sawdust-like material, which is produced during billbug feeding. On warm-season turf, delayed greenup in the spring (as the turf comes out of dormancy) and patches of dry or dead turf in summer currently are the best indicators of a hunting billbug problem.

Bluegrass billbug adults often appear on sidewalks or turf, particularly in the afternoon. If several adults are sighted, check the turf for damage.

Nate Royalty, Ph.D., is product development manager <dash> insecticides for Bayer Environmental Science.

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