Pests · Grubs
Beneficial nematodes work on grubs, but only on small grubs in warm, wet soil
For white grubs, buy Heterorhabditis bacteriophora (Hb) nematodes. Apply them in mid to late August, while the grubs are still young and close to the surface. Spray at dusk onto moist soil, water them in right away, and keep the soil damp for two weeks. They work best on Japanese beetle grubs. Results are less predictable than with chemical grub killers.
SPECIES TO BUY
Hb (Heterorhabditis bacteriophora)
NEW ENGLAND WINDOW
Early August to early September
SOIL
Above 68°F and kept moist
BEST ON
Japanese beetle grubs
Beneficial nematodes are microscopic roundworms that hunt insect larvae in the soil. They enter a grub, release bacteria that kill it within days, and then breed inside the body. Applied at the wrong time, though, they die on the grass blades and you have wasted your money. This guide covers which species to buy, the narrow late-summer window when they work in the Northeast, how to apply them, and what results to expect next to the chemical options. If you are still deciding how to treat grubs at all, start with our complete guide to getting rid of grubs.
Which nematodes kill white grubs
Several kinds of nematode are sold, and most are aimed at fleas, fungus gnats or caterpillars. For lawn grubs, the regional extension services agree on one species, with one hard-to-get alternative.
| Species | How it hunts | Use for grubs? |
|---|---|---|
| Heterorhabditis bacteriophora (Hb) | Cruises through the soil looking for hosts | Yes. UConn reports acceptable control of Japanese beetle, oriental beetle and European chafer grubs. UMass finds it much stronger on Japanese beetle grubs than on other species. |
| Steinernema scarabaei | Specialist in scarab grubs | Yes, and it is the strongest option on tough species like oriental beetle and European chafer (Koppenhöfer & Sousa, 2024). It has not been mass-produced yet, so you will rarely find it for sale. |
| Steinernema carpocapsae | Waits near the surface for passing insects | Second choice. Cornell lists it among the species that can attack scarab grubs, but UMass and UConn point homeowners to Hb. |
| Steinernema feltiae | Mobile; usually sold for fungus gnats | Sometimes sold in grub mixes. Cornell’s biocontrol team lists it alongside Hb, but Hb should be the main ingredient. |
Before you buy, figure out which grub you have. In 2023 our customers’ breakthroughs were mostly oriental beetle, and that is the species Hb struggles with most. If the beetles you see all summer are Japanese beetles, nematodes have their best chance.
When to apply nematodes for grubs
Nematodes are a curative treatment. They have to find live grubs, and they do that best when the grubs are young and feeding near the surface. In New England that is a short late-summer window.
| Source | Recommended window |
|---|---|
| UConn (Connecticut) | First or second week of August, while grubs are in their early stages |
| UMass (Massachusetts) | Mid August to early September, when grubs are present but still small |
| Maine DEP | Mid to late August in most summers |
| Cornell / NYS IPM | Mid to late August into October, after scouting confirms grubs |
Soil temperature is the other half of the timing. Cornell says Hb does best in soil above 68°F. In most New England summers that holds through August and starts to slip in September, which is one more reason to apply early in the window rather than late.
Check that grubs are there before you order. Cut three sides of a 6-inch square of sod, peel it back and count the grubs. That square is a quarter of a square foot, so multiply your count by four. UMass treats Japanese beetle and oriental beetle grubs at 8–15 per square foot, masked chafer at 6–15 and European chafer at 3–8 (UMass turf BMPs). Below those numbers, a healthy lawn usually outgrows the damage.
How to apply beneficial nematodes
Nematodes are alive when they arrive, and sunlight, heat and dry soil kill them fast. Every step below is about getting them into moist soil while they are still alive.
- Store them cold and use them soon. Keep the package in the refrigerator, not the freezer. Maine’s sheet gives you 2–3 weeks of fridge storage. UMass warns that shelf life drops with heat and that products should not be used after their first year.
- Water the lawn first. If the soil is dry, put down about 0.5 inch of water the day before, per Maine DEP.
- Apply at dusk or on an overcast or rainy day. UMass says to avoid 10 a.m. to 2 p.m. Maine prefers dusk or light rain.
- Mix and spray right away. Use water that is cooler than 86°F and spray the mix immediately. Any hose-end, pump or backpack sprayer works if you keep pressure under 30 psi (Cornell). Pull out fine filter screens, which UConn says can trap nematodes, and agitate the tank so they don’t settle.
- Water them in within minutes. UMass says within 15 to 20 minutes. Apply about 0.25–0.5 inch to wash them off the blades and into the root zone (UConn, Maine DEP).
- Keep the soil moist for two weeks. Cornell and Maine both give two weeks as the minimum. In a dry August, that means light irrigation every day or two.
Check the count on the package. Recommended rates vary a lot between sources. Maine’s homeowner sheet uses 1 million nematodes per 2,000 sq ft. The research rate in Cornell’s Hb fact sheet is about 24,000 per square foot, or roughly 24 million per 1,000 sq ft. Measure your lawn with the lawn size calculator and divide the package count by your square footage before you buy. Packages labeled for large areas often work out to very low densities.
Nematodes vs chemical grub control
UMass describes nematode results against turf grubs as erratic. In good conditions they can do very well: Cornell cites field trials in which most target pests were reduced by at least 70%, and Maine reports up to 96% against Japanese beetle grubs. A single preventive application is more predictable. Here is how the options compare in New England.
| Option | Type | When (New England) | What to expect |
|---|---|---|---|
| Hb nematodes | Biological, curative | Early Aug – early Sept | Variable. Strongest on Japanese beetle grubs. Needs warm, moist soil and live product. UConn notes they may persist for several years. |
| Milky spore | Biological, long-term | Per label; slow to establish | Japanese beetle grubs only. Can take months to build up, and results in the Northeast are inconsistent (UMass). |
| Chlorantraniliprole (Acelepryn, GrubEx) | Preventive | Mid-April – early June | Very effective on all New England white grub species (UMass). It is what we use for customers. |
| Imidacloprid (Merit) | Preventive | Mid-June – early August | Weaker than it used to be, and it does not control Asiatic garden beetle. We had a breakthrough on it in 2020. |
| Trichlorfon (Dylox) | Chemical, curative | When a sample is over threshold | Kills what it will in 1–3 days. It can’t be used on Massachusetts school grounds. |
Timing hurts every curative product, not just nematodes. UMass says that once grubs reach full size, often by mid-September, curative treatments seldom cut the population by more than 50%. For product picks and rates, see our grub control products roundup. For the calendar, see when to apply grub control.
Are beneficial nematodes worth the cost?
You are paying for a living product that can die in shipping, in a hot garage or on a sunny afternoon. To see what you are actually getting, divide the package count by your lawn size. You will also need water for two weeks of moist soil afterward. Nematodes are the better value when:
- your sample is over threshold and the grubs are mostly Japanese beetle;
- it is August, the grubs are small, and you can irrigate;
- you want to avoid insecticides near a well, pond, vegetable garden or pollinator plantings;
- you are running an organic lawn care program.
They are poor value on a lawn you can’t water, against oriental beetle or European chafer, or after mid-September. For a lawn that gets grubs every year, one spring application of a preventive is more reliable. Our spring prevention guide covers it.
When nematodes are the wrong tool: large grubs, skunks already digging, or a dry lawn.
If it is late September, the turf peels up like carpet, and skunks or raccoons are tearing it apart every night, the grubs are near full size. That is when nematodes, and curative products in general, do their worst. UMass notes that turf being dug by skunks can be lost at just 4–5 grubs per square foot. Nematodes will also die in an unirrigated lawn during an August drought.
In those cases, a fast curative like trichlorfon (Dylox) is the realistic rescue. Follow the label, including its watering-in and re-entry directions. Then plan a preventive for next May so you aren’t chasing grubs again. If the holes are small and the turf doesn’t lift, it may not be grubs at all; check small holes in the lawn overnight first.
Beneficial nematodes for grubs: FAQs
What is the best nematode for grubs?
Heterorhabditis bacteriophora (Hb). UConn, UMass, Cornell and Maine all name it for white grubs. Steinernema scarabaei works better on tough species, but you will rarely find it for sale.
Can I apply nematodes for grubs in spring?
It is a poor fit in New England. Spring grubs are large and close to pupating, and the soil is usually below the 68°F that Hb prefers. The extension windows are all in August and early September.
How long do beneficial nematodes take to work?
Infected grubs die within days, but the population drops over the following weeks. Keep the soil moist for at least two weeks, then take another sod sample. If damage continues, Maine suggests a second application.
Do I still need to water if it rains?
Applying during light rain is ideal. You still need moist soil for two weeks, so irrigate if the rain stops and the surface starts drying out.
Can I use nematodes with milky spore or a chemical grub control?
Milky spore only affects Japanese beetle grubs and works slowly, so it doesn’t replace an August nematode treatment. If you already applied a preventive in spring and your sample is under threshold, you don’t need nematodes that year.
Related guides
PREVENTION
Don’t Skip Grub Prevention This Spring
The May application that saves you the August scramble.
Sources: UConn Home & Garden: Grub Problems in Turf · UMass Turf IPM Guide: Insect Management · UMass: Beneficial Nematodes · UMass: Current Insecticide Approaches for White Grub Control · UMass Turf BMPs: Insect Management · Cornell NYS IPM: Hb Nematode · Cornell Biocontrol Bytes: Scout First · Maine: Using Beneficial Nematodes for Grub Control · UConn IPM: Beneficial Nematodes · Koppenhöfer & Sousa (2024), Insects
