To kill lawn moths and their destructive larva (known as sod webworms), your best course of action is to begin by dethatching your lawn. This removes the habitat where sod webworms hide when they are not feeding on your grass. Then, use beneficial nematodes, B.t. bacteria, or spinosad to naturally kill sod webworms. Traditional insecticides are a poor choice for controlling sod webworms because they typically only kill very young webworm larva, leaving most of the webworms alive, Plus, insecticides kill beneficial insects that naturally prey on sod webworms. So, using insecticides can actually make the infestation worse. However, Pyrethrin-based insecticides are effective at killing webworms without introducing harmful and long-lasting chemicals to your lawn.
How Do You Identify Sod Webworms?
In order to determine if patches of damaged grass in your yard are caused by sod webworms, all you need is dish soap and water. Because lawn moth caterpillars hide in the thatch of your grass, you must drive them out. To visually confirm that sod webworms are the problem, follow this process:
- Mix 2 tablespoons (30 ml) of dish soap in 2 gallons (7.5 liters) of water.
- Pour the mixture onto a damaged section of your lawn that is 12 inches square (30 cm by 30 cm).
- Allow the mixture to soak into your lawn for 5–10 minutes.
- Closely inspect the area that was soaked with the soap-and-water mixture.
- If you see 10 or more light-brown caterpillars under 1 inch (2 cm) long, your lawn is infested with sod webworms.
It’s important to perform this test before treating your lawn with pesticides. There are many causes of damaged grass, from grubs to overfertilizing. Sod webworms can be identified by their light brown color and dark brown head. They are small, only 0.5–0.75 inches long (1–2 cm). If you see these pests in your grass, it’s essential to take action immediately.
5 Best Methods to Kill Lawn Moth Larva
There are several methods for killing lawn moth larva, which are known as sod webworms. However, insecticides are rarely the best solution. This is because chemicals that kill sod webworms are mostly effective on very young larva. Not only that, but insecticides also kill pirate bugs and other insects that prey on webworms. So, our list includes methods that are sure to kill sod webworms with minimal damage to beneficial insects and pollinators.
Dethatch Your Lawn
Sod webworms live in the thatch layer between your green, growing grass and the soil surface. During the day, webworms burrow into the thatch to protect themselves from birds and other predators.
- Sod webworms hide in the thatch layer of your lawn during the day.
- Dethatching your lawn kills sod webworms and exposes them to birds and other natural predators.
- Use this lawn dethatcher to remove the thatch where sod webworms live.
- Regular dethatching prevents sod webworms from invading your lawn.
In order to eliminate sod webworms, it’s essential to dethatch your lawn. Rent a lawn dethatcher from a reputable tool dealer or home improvement store. You can destroy sod webworm habitat and save your lawn through dethatching. Plus, a dethatched lawn is far less likely to be invaded by lawn moths.
Add Nematodes to Your Lawn
In order to kill sod webworms in 48 hours, use beneficial nematodes. Nematodes are small worms that feed on the gut bacteria of sod webworms. This kills the webworms quickly, and the nematode infection will quickly spread through the webworm population, wiping out the pests.
- These beneficial nematodes kill sod webworms and are harmless to humans and other animals.
- Purchase nematodes, add them to water, then spray them on damaged areas of your yard.
- Spray nematodes on your lawn late in the day to prevent sunlight from killing the nematodes.
To use nematodes, rehydrate them by adding them to a watering can or sprayer according to directions on the product packaging. Then, water your lawn with the nematode-water mixture in the evening. Nematodes are quickly killed by sunlight, so adding them to your lawn just before nightfall allows them to enter the thatch layer, survive, and begin killing lawn moth larva.
Use Bacillus Thuringiensis
Helpful bacteria is far more effective at killing sod webworms than most pesticides. This Bacillus thuringiensis (B.t.) product contains a natural bacteria that infiltrates the digestive systems of pest worms and caterpillars, such as sod webworms. Once there, it kills the insect quickly and naturally. Even better, B.t. is harmless to humans and pets.
- B.t. bacteria infects and kills sod webworms within 48 hours—making it far more effective than most insecticides.
- Bees and other pollinators are not harmed by B.t.
- Mix B.t. with water to create a webworm-killing spray.
To apply B.t., simply mix the product with water according to product label instructions. Then, use a spray bottle or pump sprayer to spray the mixture on damaged portions of your lawn. The bacteria will quickly begin attacking the sod webworms and wipe out the infestation.
This spinosad product is another chemical-free way to kill sod webworms quickly. Spinosad is a natural byproduct of healthy soil bacteria. It kills insects by destroying the ability for the insect to control its muscles. It is extremely effective against sod webworms and similar lawn-destroying pests.
- Spinosad is a natural product that kills webworms, lawn moths, and other pests.
- Because spinosad is deadly to all insects, spray it on your lawn in the evening to avoid harming bees and butterflies.
The downside to spinosad is that it attacks all insects, including bees and other helpful pollinators. To prevent harm to bees and butterflies, apply spinosad spray to your lawn in the evening. Bees will be sleeping in their hives at night, while sod webworms crawl up from the thatch to feed on your grass at this time. This means the spinosad will kill adult moths and their larva with minimal harm to beneficial insects.
- Works quickly to control insects in your garden.
- Easy to apply application.
- Approved for organic gardening.
The best insecticide for sod webworms is Pyrethrin. We recommend this Pyrethrin pesticide for your lawn. It is powerful enough to kill webworms but is not dangerous to humans, pets, and other wildlife.
- Pyrethrin insecticides are effective at killing sod webworms quickly, with little residual damage.
- Pyrethrin has a half-life as short as 2 days, which means your lawn will be safe for people and animals shortly after treatment.
- Spray pyrethrin late in the day to target nocturnal webworms.
As with other webworm-killing products, it is best to spray the mixture onto brown patches in your lawn in the late afternoon and evening. Once night falls the webworms will crawl up from the thatch to feed on grass. Then, they will be exposed to the pesticide and killed.
Will Grass Grow Back After Sod Worms?
Once a sod webworm infestation is wiped out, your lawn will recover. The brown spots in your lawn are caused by the lawn moth caterpillars feeding on the grass. Once the pest worms are killed, your grass will gradually recover until you have a lush lawn once again.
- Your grass will grow back once sod webworms have been eradicated.
- Water your lawn twice weekly to promote grass regrowth.
- Fertilize your lawn to encourage grass to grow back quickly and prevent a weed invasion.
In order to encourage your lawn to bounce back after the worms have been killed, water your lawn deeply twice per week. Then, use our hybrid fertilizer approach to revitalize your grass.
What is the Best Insecticide for Sod Webworms?
Insecticide is a very poor choice for managing sod webworm infestation. Most insecticides are ineffective against juvenile webworms. As an added detriment, insecticide solutions kill the natural predator insects that kill sod webworms for you. Instead of traditional insecticides, try these methods of sod webworm control:
- Dethatch your lawn to remove the habitat where sod webworms hide during the day.
- Soak damaged patches of grass with water containing beneficial nematodes, which will attack and kill sod webworms.
- Apply B.t. bacteria to webworm-damaged grass to kill the pests.
- Spray spinosad insect killer on your lawn.
- Use a gentle, Pyrethrin-based insecticide to kill sod webworms without harming other insects and pollinators.
It is best to apply any spray method of webworm control to your lawn in the evening. Sod webworms come up to feed at night. So, spraying an insecticide or other product late in the day ensures the webworms will be killed.