Billbugs vs. Grubs: How to Tell What’s Killing Your Lawn

You’ve noticed brown patches appearing in your once-green lawn. Before you can fix the problem, you need to know what’s causing it. In the Treasure Valley, the two most common lawn-destroying pests are billbugs and grubs—and the treatment for each is very different.

The Tug Test

The quickest way to identify your pest problem is the “tug test”:

Grab a handful of brown grass in the affected area
Pull firmly upward

If the grass pulls up easily (like carpet):

You likely have grubs. Grubs eat grass roots from below, severing the connection between the grass and soil.

If the grass breaks at the crown but roots stay attached:

You likely have billbugs. Billbugs feed on grass stems at soil level, causing the plant to die from above.

Identifying Billbugs

Billbugs are a significant problem in Idaho lawns, particularly in bluegrass.

Signs of Billbug Damage:

Brown patches that appear in late spring to mid-summer
Grass stems break easily at the base
Sawdust-like frass (excrement) at the crown of the plant
Hollow grass stems when pulled apart
Damage often starts in sunny, stressed areas

Finding Billbugs:

Look at the base of damaged grass. You may find:

Small white larvae with brown heads
Adult billbugs: small black or brown beetles with distinctive snouts

Identifying Grubs

Grubs are the larvae of various beetles, including Japanese beetles and June bugs.

Signs of Grub Damage:

Brown patches that appear in late summer to fall
Grass rolls up like a carpet when pulled
Increased animal activity—skunks, raccoons, and birds digging for grubs
Spongy feeling when walking on affected areas

Finding Grubs:

Cut a 1-foot square of damaged turf and roll it back:

Healthy lawns: 0-5 grubs per square foot
Damaging levels: 10+ grubs per square foot

Treatment Options

For Billbugs:

Preventive treatment in late spring is most effective
Curative treatment once damage is visible is more difficult
Professional timing is critical—treatments must target larvae before damage occurs

For Grubs:

Preventive treatment in early summer before eggs hatch
Curative treatment can work in early fall when grubs are young
Milky spore is a natural option but takes years to establish

Prevention is Key

Both billbugs and grubs thrive in stressed lawns. Keeping your lawn healthy is your best defense:

Proper watering (deep and infrequent)
Regular fertilization for strong root systems
Correct mowing height (3-3.5 inches)
Annual aeration to reduce thatch

When to Call a Professional

If you’re seeing significant brown patches, it’s best to get a professional diagnosis. Misidentifying the problem—and applying the wrong treatment—wastes time and money while your lawn continues to suffer.

Our team can:

Accurately identify your pest problem
Apply professional-grade treatments at the optimal time
Help your lawn recover with proper care recommendations

Concerned about pests in your lawn? Our Billbug Control service can help protect your investment.