**Kentucky Bluegrass Billbugs** (*Sphenophorus parvulus*) are weevils whose white, legless larvae (grubs) are one of the most destructive pests of **turfgrass**, particularly Kentucky bluegrass and perennial ryegrass. The adult weevil feeds on the stems, but the primary damage is caused by the grub, which bores into the stem and then feeds internally on the crown and roots. This feeding severs the grass blades from the roots, causing distinctive dead, brown patches that are easily lifted from the soil.
Taxonomy and Classification
Kentucky Bluegrass Billbugs belong to the order Coleoptera (beetles), family Curculionidae (weevils). They undergo complete metamorphosis. The life cycle involves the adult female laying eggs near the base of the grass blade. The grub feeds inside the stem before moving down to the roots and crown. They typically have one generation per year, with damage peaking in mid-summer when the grubs are largest.
Physical Description
Adult Billbugs are black or dark reddish-brown weevils, about 1/4 to 3/8 inch long.
- **Adult Appearance (Key ID):** The body is hard and cylindrical, with a prominent, slender snout (rostrum) characteristic of weevils. They walk slowly and clumsily.
- **Larvae (Grubs):** Creamy white, legless, fat, C-shaped grubs with a brown head capsule. They are often found bent in a C or stretched out straight when inside the stem. *This key difference (no legs) distinguishes them from White Grubs (May Beetle larvae).*
- **Damage Sign:** Patches of grass turn yellow, then brown, and are easily pulled up, revealing that the stems are hollow and have been severed at or below the crown. A common diagnostic test is the **”tug test,”** which shows the stems breaking off easily, leaving sawdust-like residue (frass).
Distribution and Habitat
Kentucky Bluegrass Billbugs are native to North America and are widespread, particularly in the northern U.S. and southern Canada. Their habitat is restricted to turfgrass and lawn settings. The larvae feed exclusively on the base of grass stems and roots, while adults live on the grass or soil surface.
Behavior and Conflict
The conflict is the total destruction of turf areas.
- **Internal Stem Feeding:** The earliest damage is caused by the small grubs boring inside the stem, causing the grass blade to yellow.
- **Crown and Root Feeding:** As the grubs grow, they move to the crown, severing the plant. This damage is often mistaken for drought stress until it is too late.
- **Weevil Sign:** Adult weevils are often seen walking on driveways, sidewalks, and golf course greens in the spring and early summer as they move to lay eggs.
Management and Prevention
Control requires precise timing to target the migrating adults or the newly hatched larvae.
- Use **pitfall traps** (cups sunk into the soil) or monitor adults on driveways in the spring (April/May).
- The timing of insecticide application should occur when the adults are most active or when the larvae are first hatching (late May/early June).
- Plant **resistant turfgrass varieties**, such as perennial ryegrass and tall fescue containing endophytic fungi, which repel billbugs.
- Maintain a deep, healthy root system with proper irrigation and fertilization.
- Apply a **preventative insecticide** in late spring, timed to kill the young, newly hatched larvae as they begin feeding internally.
- **Curative treatments** in mid-summer are less effective, as the large grubs are harder to kill, but can be done if damage is severe.
Conservation and Research
Kentucky Bluegrass Billbugs are managed as a severe turfgrass pest. Research focuses on developing and expanding the use of endophytic grasses, optimizing the timing of chemical treatments based on local adult activity, and identifying effective biological controls.