By: Jean Ferdinandsen, Certified Arborist WI-0149A
If you see BB-sized holes in the trunk or limbs of your pine of spruce, it would be easy to think that someone took aim at your tree with a shotgun, but these holes may be the work of the Ips sp. beetles. These insects are commonly called engraver or bark beetles. They attack by colonizing a tree, tunneling through the inner bark to lay eggs. In the process, they interfere with sap flow and destroy the cambium, killing the tree. They can spread quickly if left unchecked. Ips beetles attack all species of pine and spruce. This insect problem has increased and has become more widespread in recent years. Drought conditions have made trees more susceptible.
People often become aware of the beetles after closely examining a tree in rapid decline or one that has recently died. In addition to the BB-sized holes, other signs of attack are etchings or engravings on the back of bark and the wood underneath. Galleries in the wood are in a “Y” or “H” shape. There may be sawdust or pitch at the exit holes. Needles of infested trees are often light-colored or chlorotic. Ips beetles will kill small- to medium-sized trees or the tops of larger ones.
Keeping a tree healthy and vigorous is the best preventive medicine to avoiding borers. Healthy, vigorous trees often have a degree of natural resistance to attacks. Start with proper planting and placement of evergreens. Recently planted trees, especially into unfavorable sites (e.g., heavy, wet or compacted soils and shade), are more likely to be attacked. Mulch after planting and maintain a 2-3" mulch layer underneath the drip line. Avoid overcrowding of trees which can lead to stress and drought conditions.
Once you have your trees off to a good start, or for existing trees, several steps can be taken to maintain tree vigor. Follow your Wachtel arborist’s recommendations for watering, fertilization and root treatments such as mycorrhizae or root stimulants. Avoid stresses on the trees such as drought conditions, injury from mowers or weed whips, soil compaction, grade changes, and flooding.
Dead and dying wood which might attract beetles should be pruned out. Severely infested or “brood” trees should be removed as they only produce more pests that can even attack neighboring healthy trees.
Borers live inside trees, making them more difficult to treat. There are 2-3 generations per year, so large numbers can build up quickly. Trunk sprays will kill adults and larvae tunneling through the treated bark layer. They will not kill larvae that have already penetrated the sapwood. Correct timing and complete coverage are necessary for effective control.
When trying to decide what steps to take with an evergreen infested with Ips beetles, your Wachtel arborist will assess the tree, evaluate the extent of damage in the landscape, and determine the need for cultural or chemical controls.
© Copyright 2005 – Wachtel Tree Science & Service, Inc.