Killing grubs will not reliably get rid of moles. This is one of the most common misconceptions in lawn care, and it leads homeowners to spend money on products that won’t solve their actual problem. Grubs are only a portion of what moles eat. Their primary food source is earthworms, and moles will keep tunneling through your yard as long as earthworms are present, which is always.
Why Grub Killers Don’t Stop Moles
Moles are carnivores, and living organisms make up about 85% of their diet. That diet includes earthworms, grubs, millipedes, centipedes, spiders, sow bugs, snails, and slugs. Earthworms are their main food source and also their primary source of water. Grubs are just one item on a long menu.
When you apply a grub killer, you may reduce the grub population, but the moles still have plenty of earthworms and other soil organisms to eat. They won’t leave. Worse, many grub insecticides actually reduce earthworm populations by up to 70%. If the earthworm population crashes enough, moles may temporarily leave the area, but this creates a different problem: you’ve now damaged the soil ecosystem your lawn depends on. Earthworms aerate soil, break down organic matter, and improve drainage. Once earthworm populations recover, the moles come back anyway.
University of Missouri extension researchers state it plainly: grub insecticides should not be used for mole control.
The Collateral Damage of Grub Killers
If you do have a genuine grub problem (brown, dead patches of grass that peel up like loose carpet), treating grubs makes sense for the lawn’s sake. But applying grub killers purely to deter moles causes unnecessary harm. Chemical grub control products containing clothianidin, thiamethoxam, or imidacloprid are toxic to bees and other pollinators. These active ingredients get absorbed by plant roots and move into pollen and nectar, poisoning bees that visit any flowering weeds in the treated area.
Carbamate insecticides are extremely toxic to earthworms. Organophosphate insecticides are similarly deadly to them. Even juvenile earthworms, which move slower and can’t burrow deep enough to escape, are more vulnerable than adults. So a grub treatment applied to chase moles can strip your soil of the organisms that keep it healthy, harm pollinators, and still leave you with moles.
How to Tell if You Have a Grub Problem
Before reaching for any grub product, make sure grubs are actually damaging your lawn. Mole tunnels and grub damage look very different.
- Mole damage: Raised ridges of soil running across the lawn, sometimes with small mounds of dirt pushed to the surface. The grass itself stays green along the tunnels, though it may feel spongy underfoot.
- Grub damage: Irregular patches of grass that wilt even with adequate water, then turn brown and die. The dead turf pulls up easily because grubs have chewed through the roots. Flip the sod back and you’ll see C-shaped white larvae with brown heads curled in the top few inches of soil.
If you only see tunnels and raised ridges with no dead patches, grubs likely aren’t your issue, and treating for them won’t help.
What Actually Works for Moles
The two most effective mole control methods are trapping and poison baits designed specifically for moles. Both target the animal directly rather than trying to starve it out.
Mole Traps
Trapping is the most reliable approach. Two types work well for different situations. Harpoon traps are easier to use when tunnels are near the surface. Scissor traps work better for deeper, subsurface runs.
Placement matters more than the trap you choose. Look for straight tunnels that follow a structural edge like a curb, sidewalk, or foundation wall. These are travel runs that moles use repeatedly, not the squiggly foraging tunnels that may only be used once. To confirm a tunnel is active, flatten a section with your foot and check the next day. If it’s been pushed back up, that’s where you want to set your trap.
Worm-Shaped Poison Baits
A worm-shaped bait containing bromethalin has been proven effective in university trials. The bait mimics the look and smell of a real earthworm, which makes moles more likely to eat it. You place it directly into an active tunnel, following the same identification method: flatten a section, wait a day, and bait runs that get repaired. Purdue University turf scientists specifically recommend this approach alongside trapping.
Castor Oil Repellents
Castor oil repellents offer a less lethal option, though results are more modest. Research from the University of Nebraska found that liquid castor oil products reduced mole activity in treated areas for over 30 days. The key is thorough watering: irrigate with half an inch of water before applying the repellent, then follow up with at least an inch of water afterward to push the product into the soil.
You can make your own repellent by mixing 6 ounces of unrefined castor oil with 2 tablespoons of liquid dish detergent in a gallon of water. Dilute that concentrate at 1 ounce per gallon and spray it over the lawn (one gallon of diluted solution covers about 300 square feet). Granular castor oil products have shown less effectiveness than liquid versions in preliminary studies, so the spray form is worth the extra effort.
If You Do Need to Treat Grubs
When grub damage is actually present, choosing the right product and timing matters. Preventive grub products are applied in early to mid-summer, before eggs hatch, and work by killing young larvae as they begin feeding on roots. Curative products are applied later, in late summer or early fall, when you can already see damage and confirm grubs are present.
Biological options like beneficial nematodes (microscopic worms that parasitize grubs) are generally less harmful to pollinators and other beneficial insects. If you use a chemical product, mow the lawn first to remove any flowering weeds. This reduces the risk of bees visiting treated flowers and picking up the insecticide through contaminated pollen or nectar.
Just know that even a successful grub treatment is a grub treatment, not a mole treatment. Your moles will still be there the next morning, happily eating earthworms.