Lawn grubs are more than a nuisance. They damage your lawn, eating the roots of the grass and eventually killing it. If you suspect they are the problem, you can look beneath the grass and into the soil below to see the number of grubs located there. A few grubs per square foot won't do much damage, but if you have five or more and start to see brown grass patches, you need to consider treatment. If you prefer not to use chemicals, you can remove the grubs organically.
Purchase beneficial nematodes from a garden center. These are micro-organisms that do not harm plants, but attack certain insects instead. There are other nematodes that are not beneficial, and harm plants; however these are not typically for sale. Look on the package to make sure it lists grubs as something the nematodes will affect.
Pour the nematode package into a garden sprayer. Read the package to determine how much space you need to cover with one package. You can mix more later if your yard is larger. Fill the sprayer with water and put the lid on. Shake the sprayer to mix it up. The amount of water is not important as long as you cover the entire space evenly.
Spray the recommended amount of space with the garden sprayer. Mix up additional packages if needed to finish covering the lawn.
Soak the lawn down with a garden hose to water the nematodes into the soil. Soak it down to at least a 2-inch depth. Wait for the organisms to do their work. Dig just under the grass after a couple weeks and count the number of grubs. Ideally you only want to see two or less in a square foot. Check back every few weeks on the progress.