Lawn Grubs in Central PA — How to Spot & Treat Them

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What Lawn Grubs Are

"White grub" is the catch-all term for the larval form of several beetles — Japanese beetle, masked chafer, June beetle, and Oriental beetle are the most common in Central PA. The adults lay eggs in lawns in late June through July. By mid-to-late July the larvae are actively feeding on grass roots. By August you see the damage above ground.

All of them look basically the same to a homeowner: a fat, C-shaped, off-white grub with a brown head and tiny legs, about ½ to 1 inch long.

How to Confirm It's Grubs (Not Drought)

This matters because the wrong diagnosis means the wrong treatment. There are two tests:

The Tug Test

Walk to the edge of a brown spot. Grab a handful of grass and pull straight up. If the grass resists — roots intact — it's not grubs. It's drought, fungus, or chemical burn. If the grass pulls up like a piece of carpet with little or no root attached, the roots have been chewed off, and grubs are the most likely cause.

The Square-Foot Dig

If the tug test suggests grubs, confirm it. Cut a 1-foot square with a shovel at the edge of a damaged area, 2–3 inches deep, and flip it over. Count the grubs in the soil and the underside of the sod.

• 0–4 grubs per square foot: normal background level. No treatment needed.
• 5–9 grubs per square foot: marginal. Healthy, well-watered lawns can tolerate this. Stressed lawns may not.
• 10+ grubs per square foot: active infestation. Treatment makes sense.

Curative vs Preventive Treatment

This is the part most homeowners get wrong. There are two completely different treatments:

Preventive — a systemic in May or June

A systemic preventive goes down before the eggs hatch, moves into the root zone, and is waiting when the grubs begin feeding. This is the reliable one — the most protection for the least material, and bee-safe when applied correctly. If you had grubs last year, this is what you book for spring.

Curative — September or October, when damage is showing

If grubs are actively destroying turf in the fall, a curative product like Dylox (trichlorfon) stops the damage and controls the grubs already in the soil. It works fast and has to be watered in immediately. This is the rescue treatment — the call we get when a lawn is peeling back in October — and it's what keeps the damage from getting worse while the repair gets planned.

What Doesn't Work

• Curative treatments applied in early spring. The grubs you'd be targeting in March or April are about to pupate into beetles — they're done eating, so killing them changes nothing about this year's lawn. That's different from the systemic preventive in May or June, which isn't aimed at those grubs at all — it's placed ahead of the eggs that haven't hatched yet.
• Treating without confirming. If you don't have 10+ grubs per square foot, you don't have an infestation worth treating.
• Milky spore alone. Milky spore only targets Japanese beetle grubs (not masked chafer or June beetle) and takes 2–3 years to establish. It can be part of a long-term plan but won't help this year.

If the Damage Is Already Done

If it's late August and you have dead patches, the grubs have already done what they're going to do. The right move is:

1. Confirm the count. If grubs are still in the soil at high numbers, a curative treatment now reduces next year's beetle pressure.
2. Plan to overseed in early September. Mid-August through mid-September is the right window for cool-season grass seed in Central PA. The damaged areas will repair quickly once watered and seeded.
3. Schedule preventive treatment for late June next year. If you had grubs once, the adults will be back to lay eggs.

When to Call Us

If you're not sure whether brown patches are drought, fungus, or grubs — send a photo or call 717-379-3248. We'll walk the lawn, do the count, and tell you whether treatment is actually worth it. Some lawns don't need it.