The answer to 'when to treat for rat' is that the best time to treat for rats is as soon as you suspect an infestation. Rats can breed rapidly, so it's important to address the problem quickly before it gets out of control. Look for signs of rat activity like droppings, gnaw marks, or nests, and take action as soon as you notice them.
Treating for rats typically involves setting traps or using rodenticides to eliminate the existing population, as well as sealing up any entry points to prevent more rats from getting in. It's generally recommended to work with a professional pest control technician who can properly identify the problem, choose the most effective treatment methods, and ensure the safety of your home and family.