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Look for signs of grubs. Check for grubs. Decide if you need to treat. Use beneficial nematodes to get rid of any type of grub. Use spores for Japanese beetle grubs. Seed and fertilize your lawn in the fall. Let your lawn grow long. Don’t overwater.
One of the major signs of a grub infestation is irregularly shaped brown patches of dead grass, but that can be caused by a number of different factors as well. If you think you may have grubs, look for other signs as well, including:  Holes in your lawn caused by birds and mammals digging in the grass to get to the grubs Grass with no roots A spongy feeling when you touch or walk on the lawn When you do find evidence of grubs, the next step is to search your lawn to inspect for the larvae. To do this, find a small spade or shovel and go to one or two of the dead patches of grass.  Dig up square-foot (30 cm by 30 cm) portions of lawn where the dead grass meets the green grass Dig to a depth of about two inches (five cm) Look for C-shaped bugs with legs on the inside of the body near the head If you find these larvae, it means you have grubs Even if you find grubs in your lawn, it’s possible that you may not have to get rid of them, depending on how many there are. A few grubs aren't actually going to hurt your lawn or cause too much cosmetic damage, especially if your lawn is healthy.  There is no need to take action to get rid of the grubs if you find fewer than five per square foot. If you find more than five but fewer than 10 grubs per square foot, you'll only need to treat your lawn if your grass isn't healthy. Regardless of the state of your lawn, you'll need to get rid of the grubs if you find more than 10 per square foot. The scientific name for these is Heterorhabditis bacteriophora, and they are microscopic, parasitic worms that invade grubs and release bacteria that kill them. It’s important to note, however, that this is a long-term method, and it can take the worms up to three years to fully control your grub problem.  For the best results, apply the beneficial nematodes in the late afternoon, and water the lawn immediately after applying them.  Because beneficial nematodes need to invade the bodies of grubs in order to propagate, you must choose between using this method or using a chemical pesticide. These worms may be sold under the name Hb nematodes, and you can buy them through gardening stores, catalogues, and online. Bacillus popilliae is a bacterium that can be used to kill the larvae of Japanese beetles. Because it’s a spore, it comes in the form of a powder that you can sprinkle on your lawn to get rid of grubs. Like the worms, using Bacillus popilliae to get rid of grubs is a long-term solution, rather than a quick fix.  To use Bacillus popilliae, you can spray it onto your lawn with water, or sprinkle the dry powder onto your grass. Like the beneficial nematodes, you'll have to choose between using Bacillus popilliae or chemical pesticides, because the spores won’t work without a grub population.  A Japanese beetle grub can be distinguished from other grubs by the end of its body. Whereas most grub bodies end in a rounded stump, the Japanese beetle grub has a pointed end. Beetles don’t tend to lay eggs in grass that’s long and thick. By seeding and fertilizing your lawn, you can repair any damage the grubs have done and deter new beetles from laying more eggs.  In spring and fall, rake away dead grass from any brown patches. Water your lawn, then sprinkle new grass seed over any thin or dead areas.  After reseeding, fertilize the lawn to help the dead patches regenerate and the new seeds to thrive. Because beetles don’t like long grass either for egg-laying, let your grass grow longer than you might otherwise once it starts to grow back. Keep your grass about two inches long. Raise the blades on your lawnmower to increase the length that it will cut the grass. An easy way to prevent your lawn from becoming a breeding ground for grubs is by letting it dry out or watering it as little as possible. Beetle eggs will die without water, so starving them of it will kill the eggs before they even hatch into grubs.  Many grubs lay eggs in July, so it’s especially important to keep your lawn dry in July and August.  Beetles will also avoid laying eggs in a dry lawn, so you should consider not watering your lawn in the last week of June as well.