Grubs in Your Northeast Lawn: How to Tell, and When to Actually Treat

In this guide

1. What grubs actually are
2. Step 1: the tug test
3. Step 2: the animal clue
4. Step 3: count them
5. If it's not grubs, what is it?
6. When to actually treat
7. Common mistakes to avoid
8. After the damage is done
9. The bottom line

Every fall, a lot of Northeast homeowners look at brown, spongy patches and assume grubs, when the real cause is often drought stress or disease. Others treat for grubs every single year "just in case" on a lawn that never had a problem. Both are expensive mistakes. Here's how to tell what's really going on, and what to do about it either way.

What grubs actually are

Lawn grubs are the C-shaped, cream-colored larvae of several beetles. In the Northeast the usual suspects are Japanese beetle, oriental beetle, European chafer, Asiatic garden beetle and a few native May/June beetles. They live in the soil and eat grass roots.

Most of them follow a similar yearly cycle:

That cycle is why timing matters so much. A product that works in June can be useless in October, and the reverse.

Step 1: the tug test

Grab a section of the brown patch and pull. If it lifts up like a loose carpet with almost no roots holding it down, that's a strong sign of grub damage. They've eaten the root system out from underneath. Drought-stressed or dormant grass, by contrast, stays firmly rooted even when brown.

Step 2: the animal clue

Skunks, raccoons, crows and other birds dig up lawns hunting for grubs. If you wake up to torn-up turf, especially in patches, grubs are a likely reason those animals are interested in your yard. It's not proof, though. Skunks also dig for earthworms.

Step 3: count them

This is the step most people skip, and it's the one that saves money.

1. Pick a spot at the edge of a damaged area, where green meets brown.
2. Use a flat shovel to cut three sides of a square about 1 foot by 1 foot, 2 to 3 inches deep.
3. Fold the sod back like a page and look through the soil and roots.
4. Count the grubs. Check two or three spots around the lawn.

As a rough guide used by many extension services, a healthy lawn can usually tolerate fewer than about 5 to 10 grubs per square foot without visible damage. Higher counts, along with root damage you can see, are when treatment makes sense. If you find only one or two, grubs aren't your problem. Look at watering, mowing height or disease instead.

If it's not grubs, what is it?

When to actually treat

There are two very different approaches, and they work at different times of year.

Preventive (best if you've had grubs before)

Preventive products are applied before eggs hatch, so the active ingredient is already in the soil when young grubs start feeding.

• Chlorantraniliprole is a low-toxicity option that can go down as early as April through June. It has a long window, which makes timing easy.
• Imidacloprid and similar products are typically applied June into mid-July. Water them in after applying, and avoid putting them down where clover or dandelions are blooming, since these products can harm bees visiting the flowers.

Preventive treatment is cheap insurance if you've had grub damage in the past few years. If you've never had a problem, you don't need it every year.

Curative (if damage is happening now)

If you find high grub counts in late August through early October, a fast-acting curative product (trichlorfon is the common one) can knock back the current generation. Water it in right away so it reaches the root zone. Expect it to limit further damage, not undo what's already dead.

Biological options

• Beneficial nematodes (look for Heterorhabditis bacteriophora) are microscopic worms that hunt grubs. They work best applied in late August to September to moist soil, in the evening, and watered in. Results vary, but they're a reasonable option if you'd rather avoid chemical products.
• Milky spore only targets Japanese beetle grubs, takes years to build up, and tends to perform poorly in cooler Northeast soils. It's usually not worth the money here.

Common mistakes to avoid

• Treating without digging. Ten minutes with a shovel can save you the cost of a product you don't need.
• Treating every year automatically. It's unnecessary cost and unnecessary pesticide use on a lawn that isn't at risk.
• Missing the timing. Preventive products in October or curative products in May don't do much.
• Forgetting to water in. Most grub products need about half an inch of water to move them down to where grubs feed.
• Ignoring lawn health. A thick, deep-rooted lawn tolerates a modest grub population without showing damage.

After the damage is done

1. Rake out the dead, loose turf. It usually comes up easily.
2. Loosen the top inch of soil and add a thin layer of topsoil or compost if the area is low.
3. Reseed. In late summer and early fall, follow the fall seeding guide. Later in the season, use dormant or frost seeding.
4. Make a note of where the damage happened. Next June, that's where you'll want to watch first, or apply a preventive product if the problem keeps coming back.

The bottom line

Dig before you buy. If the count is high, match the product to the time of year. If it's low, your lawn has a different problem, and a grub product won't fix it.

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