Practice garden sanitation. Destroy infested plants to prevent pests and diseases from spreading. In fall, uproot annuals, cut down all but evergreen and semiwoody perennials, and rake up leaves to remove cover for overwintering insects and diseases. Learn to identify pests and diseases. Before deciding whether to attempt to control a pest or disease, you must identify it.
Different measures are effective against different pests.
Use the least toxic control. Many biological controls have proven very effective in our gardens. Of course, the least toxic approach of all is to banish a long-suffering plant from the garden and grow something else instead.