Little can be done to control bark beetles once a tree has been attacked. If beetles are only in the branches or limbs, try pruning and disposing of infested limbs immediately (see below for proper disposal options). If done in the warmer months, the cuttings should be promptly and properly removed and/or treated to reduce risk of bark beetles spreading to additional trees. If the main trunk is attacked by bark beetles, the entire tree must be removed. Unless the infested tree is removed, the bark beetles can spread to other trees and kill them. They can also carry other diseases, such as dutch elm disease from the elm bark beetles. If the tree’s foliage has already changed color to straw-yellow or red-brown, then it is likely the tree has died and the beetles have already exited the tree.
Healthy trees are less likely to be successfully attacked by bark beetles. Here are some long-term ways to keep your trees and shrubs healthy and more resilient against insect attacks.
Plant species adapted to your area. Native plants from that region are the best able to thrive in local conditions.
Learn care requirements for trees and shrubs on your property. If planting, learn tree requirements regarding hole depth and width, etc., and learn correct tree care.
Determine how often to water trees based on its location, size and current weather. Pay particular attention to trees in these categories: older, slow growing, in crowded stands trees and slow-growing trees, crowded groups of trees or newly planted.
Remove any bark beetle-infested trees to prevent further infestation of other trees and shrubs. Infested trees which are removed should be taken to mills, grinding sites or covered with clear 6 mil plastic for not less than six months to prevent the spread of the beetle.
When possible, thinning and pruning is best done in late fall or winter. If you must thin your trees in spring, to maintain defensible space or for other reasons, be extra cautious not to nick nearby trees as fresh cut wood attracts bark beetles. At all times following thinning and pruning, cuttings should be promptly and properly removed and/or treated. This is even more important during warmer months of the year.
Still have questions? The Forest Stewardship Helpline is a resource provided by Northern California Society of American Foresters that can answer your questions about forest management, forest ecology and tree mortality. Call 1-800-738-TREE or e-mail firstname.lastname@example.org.