The best way to prevent and treat houseplant pests and diseases is to keep your plants healthy and clean. You should inspect your plants regularly for any signs of infestation or infection, such as yellowing, wilting, curling, or spotting of the leaves, or the presence of insects, webs, or sticky substances. You should also isolate any affected plants from the rest of your collection, and use natural or chemical remedies to get rid of the problem. Some common houseplant pests and diseases include aphids, spider mites, mealybugs, scale, fungus gnats, whiteflies, powdery mildew, and root rot.