Make sure you have a grub problem.
Reasons to apply a grub control include - a past history of grubs, if you have a sprinkler system that keeps the soil moist for egg laying, and if we have weather conditions like wet summers and lush lawns while the adult beetles are active in June.
In general, adult egg laying begins in July and root feeding begins in August. If the grub count exceeds 6-8 per square foot, you may want to consider treating for grubs. Grub controls are applied as a preventative (time frame is mid June through August). Look for a season long grub control that contains the active ingredient Chlorantraniliprole. This product is more environmentally friendly. See our publication on japanese beetles for more information