Insect attacks or various diseases can occur with little warning. An open wound on a tree that causes rot, also called a canker, on the trunk of any hardwood tree signals a serious disease. Holes bored by insects with a residue of sawdust at the base of the trunk is a sign of infestation by bark beetles. Evergreen trees will show they are ill by what is know as blister rust. If the branches take on a wilted appearance this can indicate an infestation of weevils.
Pine beetles attack the evergreen by extracting pitch from the trunk.
Thin haired evergreens will take on this appearance when being attacked by insects or when poorly trimmed. You can check for insects in an evergreen by holding a plain white piece of paper under a branch and shaking it. If there are insects on the paper the tree is sick. Trees that take up large amounts of space and appear twisted are known as wolf trees. These gnarled and older trees rob newer trees of much need nutrients and sunlight.