As with disease, the first thing in dealing with an insect problem is to identify the insect which is causing the problem. You may need to go out to the lawn or garden in the early evening, at night, or in the early morning to catch the insect in the act of eating your plant. Once you do, take a photo of it if you don't know what it is, and get help identifying it. Your county extension agent (find yours here) or local Master Gardener (find yours in WA state here) can help you.