What Are Grubs and Why Should You Care?
Grubs are the C-shaped larvae of beetles — most commonly Japanese beetles, June beetles, and European chafers. They live underground and feed on the roots of your grass. You can't see them working. Your lawn looks fine on the surface while the root system is being destroyed below.
By the time you notice the damage — patches of brown turf that pull up like a loose carpet — it's already too late to reverse it cheaply. You're looking at reseeding, resodding, or a very long recovery.
The Grub Life Cycle
Adult beetles emerge in early summer, mate, and lay eggs in your lawn soil. Eggs hatch in late July. The larvae (grubs) immediately begin feeding on roots through fall, then go dormant deep in the soil over winter.
Signs of Grub Damage
Irregular patches of brown turf that don't respond to watering. Turf that lifts up easily like a rug — roots have been severed. Increased bird, skunk, or raccoon activity digging up your lawn looking for grubs.
When Damage Appears
Most visible in late August through October. But the feeding started in late July — you just couldn't see it yet. Spring damage (March–May) can also occur as dormant grubs wake up and feed before pupating.
Prevention vs. Cure
Prevention is far more effective than cure. Curative products work on large grubs but only at higher concentrations and with luck. Preventive products applied at the right time work 75–100% of the time.
When to Apply — The Timing Everyone Gets Wrong
Here's where most homeowners go wrong: they treat grub preventer like crabgrass preventer and apply it in early spring. That's too early for imidacloprid-based products like GrubOut Plus.
Unlike pre-emergent herbicides — which are soil-temperature-driven — grub preventer timing is based on the beetle life cycle. The goal is to have the active ingredient in the root zone exactly when the newly-hatched grubs start feeding in late July. Apply too early and it degrades. Apply too late and the grubs are already too big to kill.
Early Spring (March – May)
Imidacloprid applied this early will move through the soil or partially degrade before grubs hatch in late July. You'll get little to no control when it matters most. Wait.
June 1 – June 14
Early June applications can work but you're at the edge of the window. The product needs time to water into the soil — if you apply in early June and get it watered in well, you'll be fine.
Mid-June through Early July
This is the sweet spot according to Michigan State University extension research. Imidacloprid applied now and watered in consistently reduces grub populations by 75–100%. This is the window.
July 15 – August 1
You can still apply but efficacy drops. Grubs may have already hatched and are growing. The product works best on small, newly-hatched grubs — the bigger they get, the harder they are to kill.
After August 1
Preventive products won't work effectively. If you're seeing damage now, you'll need a curative product with trichlorfon or carbaryl — and results are less predictable. Better to treat damage and prevent next year.
"The bag often says 'apply anytime May to Aug. 15' — but university research is more specific. For imidacloprid, June through early July is when you want it in the ground." — Based on Michigan State University Extension guidance
Active Ingredients: What Actually Works
Not all grub products are equal. The active ingredient determines both timing and effectiveness. Here's how the main options compare:
| Active Ingredient | Best Apply Window | Efficacy | Notes |
|---|---|---|---|
| Imidacloprid (Merit, GrubOut Plus) | June – early July | ✓✓ 75–100% | Gold standard for prevention. Must water in. Degrades if applied too early. |
| Chlorantraniliprole (GrubEx 1) | April – mid-July | ✓✓ 75–100% | Wider apply window. Less water-soluble so needs more time to reach root zone. |
| Thiamethoxam / Clothianidin | June – early July | ✓✓ 75–100% | Similar timing to imidacloprid. Often combined with other active ingredients. |
| Trichlorfon (curative) | Late July – September | ✓ Variable | Curative only. Works on existing grubs. Less predictable than preventives. |
| Lambda-cyhalothrin alone | N/A | ✗ Does not work | Binds to organic material, never reaches root zone where grubs feed. Common mistake. |
Products containing only lambda-cyhalothrin, bifenthrin, deltamethrin, or permethrin will not control grubs. These active ingredients bind to organic material in thatch and never reach the root zone. They work well for surface insects but not underground grubs.
How to Apply: Step by Step
Mow first
Mow your lawn before applying so granules fall through the canopy and make contact with the soil. Don't apply to tall grass.
Apply granules with a broadcast spreader
Use a quality broadcast spreader for even coverage. Follow the product's recommended spreader settings. Even application is critical — don't skip spots or double-apply.
Water in immediately — this step is mandatory
Apply at least 0.5 inches of irrigation right after spreading. Imidacloprid is water-soluble and needs to move into the root zone to work. Without watering, it just sits on the surface and degrades. If rain is coming in the next 24 hours, that counts.
Keep the lawn moist for a week
Continue watering normally for the following week to ensure the product reaches the root zone and stays active. Hot, dry conditions after application can reduce effectiveness.
Don't retreat unless you see confirmed grub damage
One properly-timed application per year is enough. Reapplying doesn't increase protection and adds unnecessary chemical load to your soil.
Not sure if your lawn has grubs? In mid-summer, cut a 1-square-foot section of turf, peel it back, and count the C-shaped larvae. More than 5 per square foot warrants treatment. Fewer than 5 in healthy turf usually causes no visible damage.
Use the AI ID Tool →Do You Need to Treat Every Year?
Not necessarily. If you've treated for several years and haven't seen grub damage — or evidence of grubs in your lawn or your neighbor's lawn — you may be able to skip a year. There's a common misconception that because Japanese beetles and chafers exist in your area, your lawn will automatically get damaged every year. That's not true.
Healthy, well-irrigated turf can tolerate a small grub population without visible damage. Treatment makes the most sense if you've had grub damage in previous years, your neighbors have had issues, or you're seeing a lot of adult Japanese beetles on your property in June and July.