The answer to 'when to treat for termite' is that it's best to treat for termites as soon as you suspect an infestation. Termites can cause significant damage to a home's structure if left untreated, so it's important to address the problem quickly. Signs of a termite infestation include mud tubes on the exterior of the home, wood that sounds hollow when tapped, and wings or swarms of termites.
Typically, the best time to treat for termites is in the spring or early summer when the insects are most active. This is when they're more likely to be foraging for food and more vulnerable to treatment. However, you should inspect your home for signs of termites year-round and be prepared to treat at any time if an infestation is discovered.