The brown spots, loose turf, and spongy soil grubs cause can be disheartening, but it’s possible to get rid of grubs and restore your grass just by working with nature. If you’ve confirmed a grub infestation, using beneficial bacteria, the right lawn care practices, and biological insecticides can solve the problem without harming the insects you want.
For severe infestations, chemical insecticides will get the problem under control faster.
Nematodes: Front-Line Defense Against Grubs
Nematodes are microscopic worms that kill grubs by infecting them and releasing a lethal bacteria. Apply them to your lawn, and they’ll start reducing the grub population within three days, although it takes around two weeks to see the effects.
Thousands of nematode species exist, but Heterorhabditis bacteriophora (Hb) is the one most often used to get rid of grubs. They’re living organisms that must be handled with care, so buy yours from a reputable nursery. Most can be applied with a watering can or adjustable sprayer that can release controlled doses.
Apply the nematodes in spring when soil temperatures are between 42 and 95 degrees. Choose a time in the early morning or evening after watering the lawn to protect the nematodes from light and heat. Water after application, then every three or four days if it doesn’t rain. Another application after two weeks will improve your results.
Apply them again in the fall before the soil temperature falls below 42 degrees. In a cold-winter climate, most nematodes won’t survive the winter, so you’ll need to reapply them the next year if you expect the grubs to be back.
Milky Spore: Grub-Targeting Bacteria
Milky spore bacteria (Paenibacillus papillae) cause a fatal condition known as milky spore disease in Japanese beetle grubs, but won’t harm other insects. While the bacteria won’t completely eliminate grubs from your lawn, they help keep the population below a harmful level. Because the bacteria reproduce only in infected grubs, they spread slowly and can take one to five years to become fully effective. Once established, they protect your lawn for up to 20 years.
You can find dormant milky spore bacteria in powder form at garden centers, but they become active only after warm Japanese beetle grubs ingest them. Because grubs are cold-blooded, the ground temperature must be warm enough to warm the grubs, ideally between 60 and 70 degrees. Early fall, when the grubs are actively feeding, is the best time to apply.
Spread the bacteria in a grid pattern, applying a teaspoon of bacteria powder every four feet in rows four feet apart. Then water the lawn with at least 1/2 inch water. One application is all you need. Some products can be used with a sprayer or spreader, but these are less common and usually require multiple applications.
Robins, wrens, grosbeaks, starlings, and magpies are just a few of the beetle- and grub-hungry bird species that can help protect your lawn. To attract them, set up birdhouses and create more nesting space by planting a row of dense, twiggy shrubs or small trees and allowing some overgrowth. Nesting birds are particularly helpful because they need plenty of grubs to feed their young. A well stocked bird feeder and a birdbath with a bubbler or a fountain also help draw birds.
In a lawn with minor grub damage, birds hunting for grubs can leave small holes, but these aerate the lawn, and they’re nothing compared to the damage grubs do. In a heavily damaged lawn, birds can easily tear up patches of dead, loose turf and leave a mess, but these are patches you would have had to re-seed or re-sod anyway.
Strategic Lawn Care
Grubs thrive in moist soil, so a well irrigated lawn attracts more egg-laying beetles than a dry one. That means drought can work in your favor if your lawn is healthy and your grass is a species that can go dormant, such as a tall fescue or bluegrass.
At the height of summer, stop watering your lawn for three or four weeks, but no longer than six weeks. The dry soil will discourage adult beetles and kill existing eggs to reduce next year’s crop of grubs. The grass will go dormant and turn brown, but should revive after two weeks of normal watering. If you’re not sure if your lawn can handle this treatment, consult a landscaper first.
For grass that isn’t drought tolerant or is too weak to tolerate stress, take steps to strengthen the roots against grub damage. Water thoroughly and infrequently to encourage deeper root growth. Beetles seek out short grass for egg laying, so raise your mower blade to at least 2.5 inches.
In early spring or fall, top dress with composted manure or a mix appropriate for your soil. If your lawn has more than 1/2 inch of thatch, dethatch and aerate before topdressing. Aerating in fall has the added benefit of cutting up grubs that are close to the soil surface for feeding at that time. Stick with natural fertilizers. Synthetic fertilizers can harm beneficial bacteria and nematodes.
Soap and Neem Oil: Natural Insecticides
For a homemade insecticide to control a mild grub infestation, mix 3 tablespoons liquid soap with 1 gallon water. Pure castile soap is ideal. Never use anti-bacterial soap, which kills beneficial microorganisms. Spraying this on infested areas smothers grubs while discouraging any newly arrived beetles from laying eggs.
If you need something a little stronger, but you’re not ready for chemicals yet, consider neem oil. Oil from the neem tree is renowned for its insecticidal properties, which include repelling egg-laying beetles and inhibiting feeding and growth in grubs.
Using a 70-percent neem oil concentrate product, mix 2 tablespoons neem oil and 1/2 teaspoon liquid soap in 1 gallon warm water. The water must be warm to let the oil blend properly. Spray the mixture on the lawn using a hose-end sprayer, applying a generous amount to dead patches where the grub infestation is most severe.
Chemical Grub Control
For a more severe infestation, chemical insecticides are the quickest solution, but they come with the downside of killing beneficial insects. If you go this route, choose a product specifically labeled for grub control. Many common insecticides don’t work on grubs because they sit on the soil’s surface and never reach the grubs below.
Carbaryl and trichlorfon are the two chemicals most commonly used to kill grubs. Both take between 10 to 14 days to start killing the grubs and are somewhat more effective when applied in late summer or early fall rather than in mid- to late fall. Water the lawn with around 1/2 inch of water before and after application, and keep the lawn well watered through the end of the warm season.
If you’ve had a grub problem in the past or you’ve noticed grub damage on neighboring lawns, consider applying a preventive such as imidacloprid or thiamethoxam. These work by killing newly hatched grubs before they can cause any damage.
Apply one of these chemicals in early summer and immediately water the product in. Because they aren’t effective outside the summer season, timing matters. Applying too early increases the risk the chemical will break down in the soil before summer. Too late, and grubs will be strong enough to withstand the chemical.
By using natural products such as nematodes, milky spore bacteria, and neem oil, you can get rid of grubs without harming the beneficial insects and microorganisms in your lawn. These aren’t quick fixes, though, so if your grub infestation is severe and causing extensive damage, consider applying a chemical insecticide.