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. Brown patches in late summer can also be drought stress—see drought lawn care for the Treasure Valley. For ongoing prevention plus weekly care, start a subscription.