The answer to 'when to treat for carpenter ant' is to treat for carpenter ants as soon as you suspect an infestation. Carpenter ants are a common household pest that can cause significant damage to the structural integrity of your home if left untreated. They typically become active in the spring and early summer months, so it's important to be vigilant and take action at the first signs of an infestation.
The best time to treat for carpenter ants is when you first notice signs of their presence, such as piles of wood shavings or sawdust, or if you spot the ants themselves. Carpenter ants prefer to nest in moist, decaying wood, so it's also a good idea to inspect your home for any areas that may be susceptible to water damage or rot, as these can provide ideal nesting sites for the ants.