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Lawn grub damage

Lawn grubs and the damage they cause

Lawn grubs are beetle larvae that feed on grass roots and that can cause serious damage. If your lawn is infested by grubs, there are both natural and chemical ways to fix the problem.

Do you have lawn grubs

How can you tell if your specific lawn problem is due to lawn grubs? Here are a few clues.

  • Are there areas on your lawn where the turf is wilting and turning brown? Note that this may be due to thatch, another problem altogether, but still one that requires your attention (see our page on thatch).
  • Does the affected area seem kind of spongy?
  • Are there spots on your lawn where patches of turf seem to have been upturned? This can be due to raccoons or skunks digging to get to their favorite food: juicy beetle larvae.
  • Can you grab patches of lawn and roll them back, as if they were pieces of carpet?

If you can roll back the lawn just by pulling on it, then do so and look for C-shaped whitish or yellowish larvae. You may also use a spade to cut a one square foot patch of turf that you will then dig out about 2 to 3 inches deep. If you can see ten or more larvae in a one square foot area, then you must act to control lawn grubs. You can repeat this in every location where infestation is suspected. Once the patches have been put back in place, be sure to keep them from drying out and dying. Using an endomycorrhizal inoculant may help the patches grow new roots faster.

A few words on lawn grubs

Lawn grubs are beetle larvae that develop in the ground. Freshly hatched eggs become grubs that start feeding immediately. Just as there are many types of beetles, there are many kinds of grubs. More frequent lawn grubs include June beetle grubs, European chafer grubs and the Japanese beetle grubs. These three kinds of lawn grubs have different life cycles, and may be active at different times in the year. Some will be most active in the spring, others in mid summer, others still in the fall. You may therefore have to be on the lookout at any time in the growing season. Note that when temperatures start to dip, lawn grubs tend to go deeper in the ground, and are therefore less likely to be causing problems.

Preventive measures

A preventive measure that may ensure beetles will pass your lawn is to keep your turf as healthy and dense as possible, as this makes it harder for the beetles to lay their eggs. Beetles will also tend to choose lawns where the grass is shorter, so you should keep your grass longer.

Healthy turf has a denser root system, which means the turf is more likely to resist a grub infestation. For information on how to have a healthy lawn, see our page on lawn care. But it may be an almost impossible task to have a perfectly healthy lawn in a shady location. If this is your case, see our page on grass replacement.

Natural ways to control lawn grubs

There are a few natural ways to control lawn grubs. Here are a few:

  • Enroll nematodes in your fight against lawn grubs. Heterorhabditis bacteriophora (sometimes referred to as ‘Hb nematodes’) are a type of insect parasite that have shown their effectiveness against lawn grubs. Bear in mind that these are living organisms. You must buy them fresh, use them as soon as possible, and follow the directions to the letter. Note that pesticides are lethal to nematodes.
  • Rake your lawn vigorously and overseed it (see overseeding) using grasses that contain endophytic fungi, like fescues and ryegrasses. These fungi not only make the turf more drought resistant, but they also offer protection from lawn grubs.
  • The bacterium Paenibacillus popilliae (also known as milky spore) can be used to fight Japanese beetle grubs specifically. Note that it may take a few years to establish the bacterium in your lawn, and thus control the infestation. In this case also, pesticides may not be used.
  •  Lawn grubs develop well in moist soils, so depriving them of water, especially when they start developing, may also be a way to control them. So if let your lawn become dry for a while, especially when lawn grubs are starting their development, you may kill most of them without using any chemicals.

Chemical methods

Pesticides can be used as a preventive as well as a curative measure, with the former method being much more effective than the latter. There are various products on the market that can be used to control lawn grubs, but these are only effective if used correctly and during the correct period.

Preventive products include chemicals that contain imidacloprid, thiamethoxam, clothianidin, halfenozide or chlorantraniloprole. Note these will not be effective in the spring.

Products containing carbaryl and trichlorfon may be used as curative treatments. They are the only options if high numbers of grubs are present in the fall and early spring. Their effectiveness may greatly vary depending on the period in which they are applied.

Conclusion

For most natural and chemical control methods to be efficient, they need to be undertaken at specific times in the growing season. So to be most successful in your efforts, you need to get detailed information from a specialists who know about the conditions in your area. You may contact your local botanical garden or regional agricultural service for more information on this.

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