Unfortunately, most common lawn issues appear the same, at least when they first present themselves. The best course of action is first to troubleshoot as best you can to determine what is causing the issue. This Earth-Wise Guide to Common Lawn Problems flowchart will instruct you on how to make this determination. Otherwise, you might consider having a lawn care professional come out to perform some tests and make recommendations on how to eradicate the problem.
That said, grub worms are only considered a problem when you find more than five white grubs per square foot or more. Texas A&M has some good literature on the most effective time of year to treat for grub worms, instructions on how to check your yard effectively, and the types of treatments you can use. It is also imperative to make sure your lawn is treated in a timely manner if you have found that you have more than five white grubs per square foot, as they can do some irreversible damage to your lawn in these larger quantities.