The answer to 'when to treat for stink bug' is that the best time to treat for stink bugs is in the fall, before they try to enter your home for the winter. Stink bugs typically become active and start looking for places to overwinter in September and October, so this is the ideal time to apply pest control treatments to the exterior of your home.
Treating in the fall helps prevent stink bugs from getting inside and becoming a nuisance during the colder months. However, you may also need to treat again in the spring if you see stink bugs starting to emerge from their hiding spots. It's important to target the bugs before they become established indoors.