White grubs are the larvae of several beetle species, and they destroy lawns by feeding on grass roots just below the soil surface. The good news: most healthy lawns can tolerate 5 to 7 grubs per square foot without visible damage. If your count is higher than that, or you’re already seeing brown patches and spongy turf, you have effective options ranging from preventive treatments in spring to curative products and biological controls.
How to Confirm You Have a Grub Problem
Grub damage often looks like drought stress at first. The grass thins out, wilts quickly, and turns yellow in irregular patches. As the infestation worsens, the turf feels spongy underfoot because the root system has been chewed away. In severe cases, you can grab a section of grass and peel it back from the soil like a loose carpet.
Another telltale sign comes not from the grubs themselves but from the animals that eat them. Skunks, raccoons, and armadillos will tear up sections of lawn overnight to get at the grubs underneath. If you’re waking up to divots and overturned sod, grubs are likely the reason.
To get a count, cut a one-foot-square section of turf about 3 inches deep and flip it over. Count the white, C-shaped larvae you see in the soil and at the root level. Check several spots across the affected area. Most healthy, well-maintained grass handles up to 7 grubs per square foot just fine. Stressed or poorly maintained turf can show damage at lower numbers. The threshold varies by species: Japanese beetle grubs don’t typically cause problems until you hit 6 to 8 per square foot, while May and June beetle larvae warrant treatment at just 4 to 5.
What Grubs Are and When They Feed
White grubs are the larval stage of scarab beetles. The most common culprits are Japanese beetles, masked chafers, European chafers, May and June beetles, and green June beetles. Most of these species produce one generation per year. Adults emerge in early summer, mate, and lay eggs in the soil. Those eggs hatch into tiny grubs that feed on roots through late summer and fall, then burrow deeper into the soil to overwinter. They resume feeding briefly in spring before pupating into adult beetles, and the cycle starts again.
May and June beetles are the exception. They take 2 to 3 years to complete their life cycle, which means their grubs are larger and feed over a longer period. Green June beetles cause a different kind of damage: their tunneling pushes up small piles of soil at tunnel entrances, creating an uneven, unsightly surface even before root damage becomes severe.
Preventive Treatments: The Most Effective Approach
If you’ve had grub problems in previous years or want to stop an infestation before it starts, preventive products are your best option. These work by killing newly hatched grubs while they’re still tiny and vulnerable in mid to late summer. They do not work on large, established grubs, so timing matters.
The most common preventive active ingredient in granular products (found in brands like BioAdvanced Season-Long Grub Control) is imidacloprid. Apply it between June 1 and July 15, and water the lawn with about half an inch of irrigation immediately afterward. That watering step is critical. Without it, the product sits on the surface and never reaches the root zone where grubs feed.
A newer option, chlorantraniliprole (the active ingredient in Scotts GrubEx), gives you a wider application window. Because it’s less water-soluble and moves through soil more slowly, you can apply it as early as April. Research from Michigan State University has shown that applications made before June actually work better than later ones, since the product needs more time to migrate down to the feeding zone. The ideal window is April through May, with July 15 as the latest effective date.
Curative Treatments for Active Infestations
If it’s already late summer or early fall and you’re finding large grubs actively destroying your lawn, preventive products won’t help. They’re designed for newly hatched, small grubs and lose effectiveness against mature larvae found from September through May. For active infestations, you need a curative insecticide containing trichlorfon or carbaryl. These are contact poisons that kill larger grubs on a shorter timeline, but they’re also less consistent in their results compared to well-timed preventive applications.
Curative products also require thorough watering after application to push the active ingredient into the soil. Apply them as soon as you confirm the infestation. The longer you wait into fall, the deeper grubs burrow and the harder they are to reach.
Biological and Organic Options
For a chemical-free approach, two biological controls stand out: milky spore disease and beneficial nematodes.
Milky spore is a naturally occurring bacterium that specifically targets Japanese beetle grubs. Once you apply the powder to your lawn, grubs ingest the spores while feeding. Infected grubs die within about three weeks, and as they decompose, they release billions of new spores back into the soil. The major advantage of milky spore is longevity: a single application can keep the soil inoculated for 10 to 20 years. The downside is that it only works on Japanese beetle larvae, so if your problem involves masked chafers or May beetles, milky spore won’t help.
Beneficial nematodes are microscopic worms that actively hunt grubs in the soil. The species commonly sold for grub control (Heterorhabditis bacteriophora) works against a broader range of white grub species than milky spore does. Nematodes are living organisms, so they need to be applied to moist soil and watered in immediately. They’re also sensitive to UV light, so apply them in the early morning, late evening, or on a cloudy day. You can even combine nematodes with milky spore for a complementary effect: the nematodes help spread the spores through the soil as they move.
Both biological options work more slowly than chemical treatments. They’re better suited for long-term population management than for rescuing a lawn that’s already severely damaged.
Lawn Care Habits That Reduce Grub Problems
How you manage your lawn in summer directly affects how attractive it is to egg-laying beetles. Female beetles prefer moist soil for laying eggs, and frequent irrigation during June and July can draw them to your yard, especially if surrounding areas are dry. High soil moisture also improves egg survival rates. If possible, reduce watering during peak beetle flight season (roughly mid-June through July) to make your lawn a less appealing egg-laying site.
Heavy fertilization in spring and summer is another risk factor. It pushes lush top growth at the expense of root development, which makes the turf more vulnerable to grub feeding later in fall. A better strategy is moderate nitrogen fertilization from October through December. Fall feeding builds a stronger, deeper root system that can tolerate some grub activity without showing damage. Keeping your mowing height on the taller side also encourages deeper roots and a more resilient lawn overall.
A thick, healthy lawn won’t prevent grubs entirely, but it raises the threshold at which they cause visible problems. A well-managed turf can handle grub populations that would devastate a thin, stressed one. Southern masked chafer grubs, for example, cause damage at 8 per square foot in stressed turf but can be tolerated at densities up to 20 per square foot in healthy grass.
Choosing the Right Strategy by Season
Your best move depends on when you discover the problem:
- April through May: Apply chlorantraniliprole as a preventive. This is the ideal early window for season-long protection.
- June through mid-July: Apply imidacloprid-based preventives or chlorantraniliprole if you haven’t already. Water in with half an inch of irrigation right after.
- August through September: If you find large grubs and see active damage, use a curative product with trichlorfon. Preventive products applied now will not be effective.
- October through spring: Grubs are deep in the soil and largely unreachable by any treatment. Focus on repairing damaged turf with overseeding and fall fertilization, and plan a preventive application for the following spring or early summer.
The single most important thing to remember is that timing and watering determine success more than which product you choose. A well-timed preventive applied in June and watered in immediately will outperform a curative product applied too late in the season every time.