The answer to 'when to treat for pest' is that the best time to treat for pests depends on the specific pest problem you are dealing with. In general, it's best to treat for pests as soon as you notice signs of an infestation, rather than waiting until the problem becomes severe. Early treatment can help prevent the pest population from growing and spreading throughout your home.
For many common household pests like ants, roaches, or mice, spring and summer are the most active seasons, so treating in the early spring or late fall is often recommended to get ahead of the problem. However, some pests like termites or bed bugs can be active year-round, so you may need to monitor for signs and treat as needed throughout the year.