FOR people who live near forests, poison ivy (毒藤) can be a real pain. In case you’re not familiar (熟悉) with it, poison ivy is a green weed that can cause an itchy rash (疹子) if you touch it with your skin. Farmers and gardeners have various ways of dealing with it, such as using chemical sprays (喷雾剂), but these are often harmful to the environment.