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White grubs can do a number on turf grasses and damage the roots of new plants when there are high numbers of them. Grubs are actually the c-shaped larvae of beetles that typically will emerge in the northeast in May and June. The most common is the Japanese beetle or June bug, but there are also other chafers and garden beetles as well.
Sometimes it is hard to tell if you have grubs. They will naturally be in your soil and are a food source for skunks, moles, raccoons, and opossums, so it's not usually necessary to get rid of them unless they are doing significant damage to plants or grasses. If you start seeing patches of dead grass or see a lot of dig marks from animals, you may need to start controlling your grub population.
To determine if you need to start controlling grubs, you may want to lift the sod of a 12" x 12" area that appears to have been damaged by grubs. If you see more than two grubs per area, taking measures to control them may be in order. If you don't see any grubs, either they have emerged from the ground as beetles already or there is another reason why your turf grass and plants are dying or getting damaged.
I would suggest avoiding chemical grub killers because they can damage the structure of the soil as well as killing off beneficial critters like worms and nematodes. Usually people who rely on chemical controls the most, have the most problems with grubs when they stop using the chemical control, so be patient if you are switching from organic to chemical controls as it may take a couple of years to get everything back in balance.
The best course of action, in my opinion, is to apply beneficial nematodes in the spring to control all grubs. This type of control would need to be applied on a yearly basis until populations get under control as the nematodes generally do not live through the winter months in cold climates.
If you have a lot of Japanese Beetles in your yard in June and July, you may want to apply Milky Spore in August. Milky Spore is actually a bacteria that only affects the grubs of this type of beetle and can last for many years with just one application. You can read more about Japanese Beetles and controlling them by checking out my other article here.
Once you have gotten your grub problem under control, you will want to avoid over-watering and over fertilizing your lawn and gardens as grubs are attracted to moist conditions. Switch to organic fertilizers and native plants that don't require lots of water to survive. With the change in our climate happening right before our eyes, you may find that you have to re-evaluate the plants in your garden every five or ten years to see if it costs too much time, energy and water to maintain them.