Science, Tech, Math › Animals & Nature Most Common U.S. Tree Pests A Guide to Insect and Disease Pests of the Forest Share Flipboard Email Print Juvenile and adult aphids, aphid eggs, and moulting individual on Helleborus niger. Michel Vuijlsteke/Wikimedia Commons/CC BY-SA 3.0 Animals & Nature Forestry Pests, Diseases, and Wildfires Tree Identification Basics Arboriculture Tree Structure & Physiology The Science Of Growing Trees Conifer Species Individual Hardwood Species Tree Planting and Reforestation Amphibians Birds Habitat Profiles Mammals Reptiles Wildlife Conservation Insects Marine Life Dinosaurs Evolution View More By Steve Nix Forestry Expert B.S., Forest Resource Management, University of Georgia Steve Nix is a natural resources consultant and a former forest resources analyst for the state of Alabama. He is a member of the Society of American Foresters. our editorial process Steve Nix Updated August 08, 2018 Trees in a forest or landscape are under constant attack by insects and pathogenic diseases. A tree in good health can withstand most of these pests for a while but can be overwhelmed as site conditions and pests relentlessly rob the tree of its vigor. The best way to prevent tree mortality is to improve conditions that support tree health. Take time to observe your trees for signs of stress — dying limbs, bleeding cankers, visible fungi, yellowing and drying of foliage. Remember that the best way to protect a tree from pests including disease and insects is to have a healthy tree. A healthy tree starts with its first year of life. Forest Disease Pests The vast majority of forest and landscape diseases attack trees in the form of bacterial pathogens and fungal infections. Many will not kill a tree but can have a cumulative effect on a tree's vigor and health over time. A few will rapidly kill trees and demand that you keep a watch for symptoms. Identification of Common Tree Disease Pests: A guide to common diseases including root rots, blights, cankers, wilts, and decline. Start your review with the most often seen tree diseases in North America: The Common Hardwood DiseasesThe Common Conifer Diseases Also, review "worst of the worst" tree disease pests in North America in conifer killer diseases and hardwood killer diseases. Forest Insect Pests Insects that attack trees come in many sizes and shapes. The beetles consume leaf parts and inner bark; the aphids, leafminers, and moths defoliate; the borers consume wood; the gall-making wasps deform limbs and leaves. Not all insects will kill a tree, but the "killers" listed can be certain death when insect populations explode. Identification of Common Tree Insect Pests: A guide to common insects including beetles, borers, caterpillars, weevils and adelgids. Also, review "worst of the worst" tree insect pests in North American include conifer insect killers and hardwood insect killers.