About several tree diseases that can stunt or injure a tree over time. From University of Illinois Extension. Forestry Images - Quality photographs of forest insects and disease organisms. Contains image search or browse by categories. Gypsy Moth - The gypsy moth is a serious threat to trees including maples, oaks and elms.
Caterpillars feed on leaves, weakening the tree.
Oak Wilt - Oak wilt is a devastating fungal disease that attacks red oaks, white oaks and live oaks of North America. Learn how you can identify and control this oak tree disease. Powdery Mildew - Powdery mildew is a fungus that attacks the leaves of various plants including poplar and willow trees and roses. Sudden Oak Death - Created by the University of California's Sudden Oak Death Research Team, this site addresses the increasing number of oak trees in California that are dying from the fungal disease Phytophthora, and the effects the infestation is having on forest ecology. Tent Caterpillars - The Eastern tent caterpillar affects black cherry trees and other fruit and shade trees.