Worms

How to Get Rid of Grubs

If your lawn is brown and wilting even if you water it every day, you may just have a grub infestation. Grubs are white, worm-like organisms curled up underneath the soil. These creatures are voracious eaters of roots, which means your lawn is virtually a buffet for them. If you don’t do anything about it, your lawn will soon resemble a desert. The following tips can help you get rid of grubs for good.

What are Grubs?

The best way to get rid of grubs is do it systematically. This requires an understanding of what grubs are and what they do. Although they look like worms, grubs are actually larvae of scarab beetles, like Japanese beetles, Oriental beetles, and European beetles. They are found underneath the top soil of your lawn because they feed on the roots of your plants.

It’s a Grub’s Life: The Grub’s Life Cycle

Japanese beetles best represent the life cycle of a typical grub. In the United States, adult Japanese beetles emerge from the ground and mate in late June and early July. In July, female beetles spend two to three weeks laying up to 60 eggs in the surrounding soil, including your lawn. Eggs hatch about two weeks later, depending on soil temperature and moisture.(Learn how to get rid of japanese beetles)

The grubs that hatch from the eggs spend most of August feeding on grass roots underneath the soil. They feed close to the surface, so they are very vulnerable to chemical and biological insecticides at this period. By October, damage to the lawn should already be apparent as the grubs become larger and consume more roots. Trying to eradicate them in fall is usually futile because they have developed the ability to dig deep into the ground. Spraying insecticides in spring also generally doesn’t work because they are already large and the span of time for treatment is short.

How to Sample Your Lawn for Grubs

The first step to eradicate grubs is to determine if you indeed have a grub problem. Grubs are pretty common in lawns in some states, and as long as there are not too many of them, your lawn is safe from significant damage. To find out whether you need to take action, you have to sample your lawn for grubs.

  • Step 1: Begin sampling in August so you’ll catch the grubs while they are still small and close to the soil’s surface. Look for areas on your lawn that are likely carriers of grubs. The most likely feeding grounds of grubs are the following:
    • Areas where green grass meets brown grass
    • Areas that are not shaded by trees or shrubs
    • Sites where you’ve seen lots of adult beetles in July or August
    • Irrigated lawns surrounded by dry turf
    • Green lawns with good soil moisture and temperature
    • Damaged areas where raccoons and skunks dig up grubs to eat
  • Step 2: Draw a simple map, and mark the highly suspicious sites with Xs. Ideally, sampling sites should be 10 feet apart. You can also mark more Xs for low-priority areas that are 20 to 30 feet apart.
  • Step 3: Get a watering can, a shovel, a piece of cardboard, a pen, and take your map with you to the sampling sites. Use the shovel to remove some of the soil, then examine the contents of the soil on the cardboard.
  • Step 4: The area should be approximately 1/10 of a square foot of turf. Count the number of grubs you see, and jot it down on your map. Multiply the number by 10 to get the number of grubs per square foot.
  • Step 5: Replace the soil, and water the area thoroughly with the watering can. Move on to the next site until you finish all the Xs.

Do You Have a Grub Problem?

After sampling your lawn, it’s time to know whether you have a grub problem or not. Researchers in upstate New York have found out that only 20 percent of home lawns require treatment. Here’s the recommended thresholds for grub population, and what they mean for your lawn. These numbers are based on grubs per square foot.

  • 0 to 5 grubs: You don’t need to treat your lawn.
  • 6 to 9 grubs: If your lawn is healthy and the grass has strong roots, then it can still withstand the grubs without much damage. On the other hand, if there are some damaged sites caused by digging skunks and raccoons, it’s probably a good idea to treat highly populated areas. (Tips on how to get rid of skunks)
  • 10 or more: Definitely treat your lawn because grubs will do significant damage. Sample again in a few areas after treatment to see whether your insecticide was effective.

Getting Rid of Grubs in Your Lawn

Once you’ve determined where the grubs hide, it’s easy to drastically reduce their numbers. The following are tried and tested methods of grub control:

  • Pesticides in August: Most soil insecticides in the market today only last for three weeks or less, which means you have to apply them when grubs are actively feeding. Take note that no insecticide is 100% effective, but you should be able to kill 75% to 90% of grubs on your lawn if you do it correctly. Apply the pesticides in August when the larvae are most vulnerable. You may apply the pesticides repeatedly to increase their effectivity.
  • Bomb them with bacteria: Bacillus popilliae, also known as milky spore, are very effective against Japanese beetles. The bodies of grubs turn milky white when they feed on these bacteria, and they die. Milky spores are available commercially and you must use them for three to five years to provide lasting controls.
  • Control them with nematodes: Nematodes are parasitic worms that can effectively kill white grubs. Studies show that nematodes in the genera Heterorhabtitis and Steinernema can control 50% to 80% of grub population. Like milky spores, these organic pesticides are also commercially available.
  • Modify your lawn or garden: Certain species of beetles prefer specific host plants, so you can get rid of these plants to get rid of the grubs; for instance, if Japanese beetles are common in your area, do not plant grapes, lindens, and roses on your garden or lawn. May and June beetles like oaks, while green June beetles prefer ripening fruits such as peaches. Also, beetles don’t seem to like tall fescues as much as they like perennial ryegrass and Kentucky bluegrass.
  • Deny them water: Grubs love moist soil, so if your lawn can handle it, do not water in July and August when grubs are actively feeding. Don’t do this, though, if your lawn is already too dried up.
  • Preventive pesticides: Using pesticides before August is usually not effective, but it may work for areas where the population of adult beetles is quite large. Recommended pesticides include: imidacloprid, isofenphos, and isazophos.
  • Fall pesticides: Like preventive pesticides, fall pesticides don’t work as well as August pesticides. By this time, the grubs are already 70 to 80 times the body weight of a newly hatched grub. They are voracious eaters, and they dig deep down to avoid the cold weather. If you still want to use pesticides however, apply diazinon, trichlorfon, and isazophos for best results.
  • Spring pesticides: Spring pesticides are as ineffective as fall and preventive pesticides, but they may still help reduce the numbers of grubs. They usually don’t work because grubs are already quite large during spring, and they only feed for a short period of time. Experts also recommend diazinon, trichlorfon, and isazophos for spring pesticide application.
  • Let nature do its job: Even if you don’t do anything about the grubs, rest assured that nature has its own controls against them. Tiphia wasps, birds such as meadowlark and cardinal, and raccoons and skunks all feed on grubs. There isn’t sufficient evidence, though, that moles also eat grubs.

Sample your lawn regularly to prevent the proliferation of grubs. Tell your neighbors to take care of their lawns too, because scarab beetles distribute their eggs more evenly if there are more healthy lawns around. In fact, some people get grub infestations because their lawns are the only healthy turfs around the area. If all people maintained their lawns and gardens properly, grub infestations would surely be reduced. If you’re interested in reading this article, might as well read how to get rid of beetles.

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About the author

Nicole Harding

2 Comments

  • The article reads: “Spraying insecticides in spring also generally doesn’t work because [grubs] are already large and the span of time for treatment is short.”

    But then farther down, the article reads: “Step 1: Begin sampling in August so you’ll catch the grubs while they are still small and close to the soil’s surface.”

    So which is it? Are grubs still small in August, or are they already large by spring?

  • I have tried to grow roses. Every year the beetles eat them up. How can I stop this. I have grubs in this area. Hoping you can tell me what to do. Thank You.

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