Prevention is key to organic pest control. Start by “creating a healthy growing environment,” says Jack Algiere of Stone Barns Center in Pocantico Hills, New York. Also, be on the lookout for pests “before you see damage to your plants,” advises Peter Jacobsen of Jacobsen Orchards in Yountville, California. But what if pesky insects—like aphids, mites, or beetles—or powdery mildew won’t go away? Try these expert-recommended, eco-friendly solutions.