Grubs are from the Japanese beetle. Japanese beetle will emerge from the ground around Memorial Weekend. Their favorite food are linden trees, roses, grapes and soybean fields which we are surrounded by. They return to your turf to lay larve. The larve become grubs around the 4th of July weekend. The grubs will continue to eat from this point until the beetle emerges the following spring Memorial weekend. The best control is a preventative treatment at the end of June to July application. If left untreated there is a more expensive late summer/fall application as well. If you wait you will have the damage to contend with.
This photo shows you just how much damage grubs can do to a lawn.
This type of damage to your plants and trees are a result of Japanese Beetle Infestation.