The timeframe to prevent grubworms starts right now! We have from now until about the middle of July to effectively prevent grub damage.
Grub prevention does not completely keep grubs out of your lawn, but it kills young grubs before they have a chance to feed on your lawn. Once they reach a certain size, the preventative no longer works and you will have to use a different product (which by that time they will have begun eating your turfs root system).
It is very important to get this done, ESPECIALLY if you have had grubs in the past, or if you have seen a lot of June bugs on your property.
There is no real way to predict whether you will have a grub infestation or not without the preventative, so don't delay!