Bluegrass billbug

What is bluegrass billbug?

The bluegrass billbug is a small weevil, or snout beetle, and the most common billbug on home lawns in Pennsylvania and New England. Penn State says it causes the most billbug injury to Pennsylvania lawns, where Kentucky bluegrass is its main host. It also feeds on perennial ryegrass and fescues.

The adults do little harm. The larvae do the damage. Females chew a hole in a grass stem and lay an egg inside. The young larva tunnels down the inside of the stem, then drops into the thatch and feeds on the crown and roots. Turf goes from green to spotty straw-colored patches in late June through August. Because the stems are cut at the crown, they pull up easily and break off, leaving roots behind in the soil, along with fine sawdust-like droppings.

Billbug damage is often mistaken for drought, salt damage along walks, or grub damage. Two quick checks help: tug on stems at the edge of a patch, and look for that sawdust-like frass. Billbug larvae have no legs, which sets them apart from white grubs.

Signs and damage

• Spotty, straw-colored patches scattered through the lawn from late June through August.
• Damage that often starts along driveways and sidewalks and can look like salt damage, but shows up in July.
• Wilting that does not respond to watering, with patches browning out within days.
• Grass stems that snap off at the crown when tugged, leaving the roots in the soil.
• Fine, sawdust-like droppings (frass) at the base of stems and in the thatch.
• Small snouted beetles walking across driveways and sidewalks on sunny spring days.

Bluegrass billbug identification: what to look for

• Adult: About 1/4 to 3/8 inch. Gray, brown or nearly black weevil with a long snout, a broad thorax about one-third of its length, and a pitted back. Dried soil can change its color.
• Larva: Legless, plump, white to cream with a hard brown head. About 1/16 inch when young and 1/4 to 3/8 inch when full grown.
• Eggs: White and kidney-shaped, laid inside a hollowed chamber in a grass stem. They hatch in about 7 to 14 days.
• Damage: Straw-colored patches; stems hollowed and cut at the crown; sawdust-like frass; turf pulls loose easily.
• Timing: Adults active on warm spring days (late April to mid-May in Pennsylvania). Larval damage from late June through August, peaking in July and August.

Life cycle

One generation a year. Adults spend the winter in leaf litter, thatch, hedgerows and along building foundations. They become active when temperatures pass about 65 degrees F, from late April to mid-May in Pennsylvania (UMass watches for them on pavement in late May or early June in New England), and walk to the lawn across pavement. Females lay eggs in grass stems from late April through June. Larvae go through three stages over 5 to 8 weeks: the first two feed inside the stem, then they drop to the thatch and feed on crowns and roots. When feeding ends in mid to late July, they move 1 to 2 inches into the soil to pupate. New adults emerge in late August and September and feed a little before moving to winter shelter (Penn State, UMN, UMass).

When to look: Watch pavement next to bluegrass lawns for walking adults on sunny days from late April into early June. Check for larval damage from late June through August.

Bluegrass billbug look-alikes

A few things get mixed up with it:

• Hunting billbug (Sphenophorus venatus vestitus): A related billbug that Penn State lists among the billbugs that attack turf. Adults have a smooth Y-shaped area behind the head and curved marks like parentheses on the sides of the thorax (NC State).
• Annual bluegrass weevil (Listronotus maculicollis): About half the size, with antennae near the tip of the snout. It attacks only short-mown golf turf, not home lawns.
• White grubs (Scarab beetle larvae (several species)): Grubs are C-shaped with six legs and eat roots, so turf peels back like a carpet. Billbug larvae are legless and leave sawdust-like frass in hollow stems.

How to control bluegrass billbug

Cultural control

• When overseeding, use endophyte-enhanced perennial ryegrass or fescue, which can repel billbugs. UMass notes endophytes are not found in Kentucky bluegrass, but some bluegrass varieties resist billbugs on their own.
• Keep the lawn watered and moderately fed; UMN says healthy turf may not need treatment at all.
• Count adults on pavement on sunny days in late May or early June: UMass says two or more per minute suggests damage to the nearby turf in about six weeks.
• Inspect a square foot of turf at the edge where damaged grass meets healthy grass, digging into the thatch with a trowel to find larvae.
• Cornell notes endophytic tall fescue and perennial ryegrass reduce billbug survival, and suggests avoiding pure Kentucky bluegrass where billbugs are a repeat problem.

Biological control

• Insect-parasitic nematodes, especially Steinernema carpocapsae, can be applied when small larvae are present, usually late June or early July. Water right after and avoid hot, dry, breezy midday applications (UMass, Penn State).
• A natural fungus, Beauveria bassiana, sometimes covers billbugs in white fuzz but rarely keeps them below damaging levels (Penn State).

Chemical control

Timing is everything. Penn State says spring treatments aimed at adults before they lay eggs work best, timed with trap counts or degree days; University of Minnesota says about 10 days after adults are first seen, with May as the key month. Cornell targets adults between mid-May and late June, before egg laying, with light watering afterward. UMass finds the adult window narrow and prefers June, aimed at small larvae. Summer rescue treatments work poorly, and University of Minnesota says not to treat after mid-July, when larvae have moved into the soil to pupate. University of Minnesota names imidacloprid (slow-acting, water it in), trichlorfon (faster) and halofenozide (a growth regulator). Use only products labeled for this use; the label is the law.

Use only products labeled for this pest and this site; the label is the law. For trees, work with an ISA Certified Arborist. If you hire someone to apply pesticides, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Prevention

• Use billbug-resistant Kentucky bluegrass varieties or endophyte-enhanced ryegrass and fescue in new seedings.
• Watch the pavement edges every spring for walking adults.
• Check lawns at the edge of pavement in July before damage spreads.

When to call a pro

Call a licensed pesticide applicator (see our pesticide applicator license guide) if a lawn has a history of billbug damage and spring monitoring shows lots of adults, or if larval counts reach about 6 to 12 per square foot.

Related guides: Weed identification guide · All pests and diseases

Questions about bluegrass billbug

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