to all the ads for grub control in spring. It's just about the least effective time to try to control grubs, insects then so close to maturity that they're next to impossible to reach and kill. Baby grubs, that's what we should go after. Babies are easy to kill, and they have not yet done much damage, if any. Do that in August and start with beneficial (predatory) nematodes before any of the broad spectrum insecticides.
So why do all the lawn care companies push it? Same reason jewelry companies run lots of ads around Christmas -- because we're thinking about our lawn and willing to spend money.
Do make sure before you apply grub control at any time, that grubs are actually your lawn's problem. Dig some test patches and see how many grubs are there. Far more lawns are dying of compacted soil, too little water or fertilizer. Unnecessary insecticide is such a waste of money and time to do nothing but start a bad ripple in your local ecology.