How To Identify & Get Rid Of Bluegrass Billbugs

Preventing Billbug Damage To Your Lawn

One of the more stealthy but destructive pests that can impact turfgrass, particularly Kentucky bluegrass, is the bluegrass billbug. Also known as bluegrass weevils, these small beetles and their larvae may not be as widely known as white grubs or chinch bugs, but their damage can be just as severe if an invasion is not caught in time. 

Keep reading to learn all about how to identify billbugs and prevent the damage they cause to your lawn!

What Do Bluegrass Billbugs Look Like?

Adult bluegrass billbugs are small beetles, typically measuring about 1/3 inch in length. They belong to the weevil family, and their most distinguishing feature is their long, curved snout or "rostrum," which they use to chew into grass stems and deposit eggs. Their color ranges from grayish-brown to black, and they often have a pitted or rough texture on their hardened wing covers, giving them a somewhat dusty or dirty appearance.

Despite their relatively small size, they’re not difficult to spot if you know what to look for. They’re most commonly seen walking slowly across sidewalks or driveways in late spring to early summer. Unlike many insects, they’re not strong flyers, so they often travel by foot. When disturbed, they may drop and play dead, making them harder to detect in the turf.

What Do Their Larvae Look Like?

Billbug larvae are legless, white to cream-colored grubs with a brown head capsule. They closely resemble white grubs from beetles like scarab beetles, but the key difference is the lack of legs. Billbug larvae typically measure about 1/4 inch long when fully grown and have a distinctive C-shape when curled up.

Because larvae do most of their feeding underground or within the grass crown, they’re not often seen unless you’re digging into damaged turf. If you pull up a patch of declining grass and see hollowed-out stems and small, legless larvae near the crown, you’re likely dealing with billbugs.

Billbug Bluegrass Life Cycle

Understanding the life cycle of bluegrass billbugs is crucial to effective management. These insects undergo complete metamorphosis, from egg, larva, pupa, and adult. There is typically only one generation per year, although there may occasionally be more in warmer climates. Most damage is done during the larval stage, so recognizing the cues for egg-laying and early larval feeding can help time treatments effectively.

• Spring Activity: In late April to early May, as soil temperatures warm, adults emerge and begin feeding on grass stems. Females use their snouts to chew a small hole into a grass stem and deposit a single egg inside.
• Larval Stage: After hatching, larvae begin feeding from within the stem, eventually boring downward into the crowns and roots. This hidden feeding phase is when the most significant damage occurs.
• Pupation: After feeding for several weeks, larvae pupate in the soil. This stage can last a few days or over a month, but 3 weeks is the common length of pupation for bluegrass weevils.
• New Adults: Adults begin to emerge in late summer but do not reproduce again that season. Instead, they seek overwintering sites and restart the cycle the following spring.

Lawn Damage Caused By Billbugs

Both adult and larval bluegrass billbugs contribute to turf damage, but the severity and visibility of that damage differ greatly between the two stages. Adult billbugs begin feeding in the spring as they emerge from overwintering, chewing small notches and holes in grass stems and blades. This initial feeding is relatively superficial and often goes unnoticed, though it can weaken the grass and make it more susceptible to environmental stress. 

The more significant harm occurs once females lay their eggs inside the grass stems. When the larvae hatch, they feed from within, hollowing out the stems as they move downward into the crowns and roots of the plant. Because the larvae are legless and live out of sight, they can cause extensive internal damage before any symptoms appear above ground. 

As they feed, they sever the plant’s ability to absorb water and nutrients, resulting in wilted, discolored patches of turf that can easily be mistaken for drought stress or disease. In severe infestations, the lawn may develop large dead patches that fail to recover, particularly during the hot, dry months of summer. Spongy turf is a key indicator that billbug grubs have eaten away the roots and crowns of your lawn. 

Warning Signs Of Billbug Infestation:

• Turf that turns brown or yellow in irregular patches, especially in sunny areas.
• Grass blades that appear chewed, frayed, or ragged (indicative of adult feeding).
• Stems that are hollow and break easily at the crown when pulled.
• Turf that lifts easily from the soil with little resistance, revealing damaged roots and larvae.
• Presence of small, white, legless grubs with brown heads near the soil surface.
• Lawn decline that worsens during dry weather, even with regular irrigation.

What Attracts Them?

Bluegrass billbugs are especially drawn to Kentucky bluegrass, although they may also feed on perennial ryegrass, fine fescue, and even some warm-season grasses like Zoysiagrass. Several factors can make a lawn more susceptible to billbug infestation. Being mindful of these risk factors can help you assess your lawn’s vulnerability and take preventive steps before infestations become severe. 

• Monoculture Lawns: Lawns that consist of a single grass species, especially Kentucky bluegrass, are more attractive to billbugs.
• Thatch Buildup: Thick layers of thatch provide shelter for adults and emerging larvae.
• Excessive Nitrogen Fertilization: Over-fertilized lawns with lush growth are more appealing to feeding adults.
• Dry Conditions: Larval damage often goes unnoticed until a drought sets in, which can quickly accelerate turf decline.

How To Prevent & Control Billbugs

Once you know how to spot the warning signs of a billbug invasion in your lawn, you can take measures to prevent or mitigate the damage they cause. Controlling bluegrass billbugs requires a combination of proper lawn care practices and, in some cases, pesticide applications.

• Choose Resistant Grass Varieties: If you're establishing a new lawn or overseeding, consider using endophyte-enhanced varieties of perennial ryegrass or tall fescue. These naturally repel billbugs.
• Reduce Thatch: Aerating your lawn regularly and dethatching when needed helps reduce insect habitat and improves root health.
• Irrigate Properly: Water deeply but infrequently to encourage deep root systems. Avoid overwatering, which can create favorable conditions for pests and disease.
• Balanced Fertilization: Use a slow-release fertilizer and avoid heavy nitrogen applications in the spring, which can attract egg-laying adults.
• Preventive Applications: Systemic insecticides such as imidacloprid or clothianidin are most effective when applied in late spring, just before egg hatch. These products move into the plant tissue and kill larvae as they begin to feed.
• Curative Applications: Once larval damage is visible, treatment options are limited. Curative products like trichlorfon or carbaryl may provide some relief, but they’re less effective than preventive treatments and can harm beneficial insects if misused.

Though billbugs and weevils are not dangerous to humans, the damage they cause to your lawn can be a very costly inconvenience that warrants pest control services. It’s a good idea to consult with a local lawn care professional to time applications properly and limit damage to beneficial bugs and other critters. Contact Holmes Lawn & Pest today for more information on the best lawn pest control in Utah!