The best way to prevent disease and insect outbreaks is to keep your trees healthy. Just like people, trees can be stressed, which can make them more vulnerable to insects and disease. For example, when trees are attacked, sometimes they can push out pests by moving large volumes of sap through their branches — but not if they’re too crowded or aren’t getting enough water. Like people, if they aren’t healthy, they can’t fight off minor infections.

Maintain a diverse woods. Once a tree is attacked, insects and pathogens can spread to neighbors. Many pests only attack a single species, so it’s useful to have a mix of trees in your woods. Also, keeping trees farther apart helps them stay healthy by getting the light, water, and soil nutrients they need — although it can also help weeds grow on the forest floor.