You need to get a lawn fertilizer type product that contains grub giller. Grubs are these gross white worm looking bugs that live in the roots of the grass & attract the moles as the moles eat the grubs. Follow the package directions. It is usually best to do the application before a good rain and this is also a good time of year to do this. Be sure to by enough product to get the job done right the first time! If you don't get the problem under control it can become quite costly. Friends of mine actually had to remove their whole lawn and replant it. Good luck!