Tree Tips - How to Prevent Insect Pests

Posted: 3/13/2019 8:52:26 AM

Due to the past hot, dry summers, the area is experiencing an increase in pest activity such as native bark beetles. Bark beetles are about the size of a grain of rice, and kill trees relatively quickly by feeding in the conductive tissue just beneath the bark. Stressed trees are more likely to be targeted by these insects. Below are tips from local entomologist, Erika Eidson with the Idaho Department of Lands, to prevent bark beetle attacks.

1.  Keep trees healthy and vigorous. Maintain appropriate tree spacing to reduce competition for water and sunlight. If possible, apply supplemental water during periods of low rainfall. Avoid soil compaction within the drip line of the tree canopy. Avoid damage to the trunk. Take care not to over-fertilize, especially in dry years, because fertilizers can burn the tree roots. Remember that pesticides should always be used according to the label instructions, and the use of some pesticides may kill off important insect predators that help keep pest populations in check.

2.  Keep your site clean. Logs and slash from live trees that were recently cut or damaged can attract bark beetles to your property. Remove or destroy winter storm damage before April. If you plan to cut live pine trees but do not plan to remove or destroy the material right away, do the work in fall, but before winter. This is generally after beetle flight period, but still allows enough time for the logs and slash to dry out before the next season. Trees that have already died and dried out are no longer host material for damaging bark beetles and can be cut at any time. Remember that many pesticides are not labeled to treat firewood, and should not be sprayed on wood you plan to burn.

3.  If you have bark beetle-infested trees, remove or destroy the infested wood materials. For a period of time, bark beetles can still emerge from the logs of an infested tree even after it has been cut. They can then attack additional trees in the area. Be sure to check the green trees around the infested area for signs of bark beetle attack, such as pitching or reddish dust where beetles have bored in. Often people notice and cut the dead trees with red needles, but by this stage the beetles may have already emerged from the dead trees and attacked the nearby green trees. Remember it can take months for the needles of an attacked tree to fade from green to red. A professional forester or entomologist can help you identify attacked trees that currently contain live bark beetles.

4.  Generally, pesticides only work preventatively against bark beetles. Trees that have already been successfully attacked cannot be saved and should be removed. Full-coverage bark spray insecticides are available and can provide short-term protection for high value trees that have not yet been attacked. Due to the cost and sometimes difficult application, this treatment typically isn’t recommended unless there is a viable insect threat nearby. Deterrent pheromone pouches are available to protect some trees from a few species of bark beetles, but must be applied appropriately in order to be effective. Homeowners should seek professional advice from an entomologist when using pheromones.

5.  The large beetles often seen in firewood piles and on dead trees are wood borers, not bark beetles. They help to recycle dead wood material and are not cause for alarm. Bark beetles are actually rarely seen, because they are so small and spend almost their entire life beneath the bark.


Attached is a fact sheet with more information. Since there are many different species of bark beetles, and each one has a different lifecycle and treatment, it is important to identify which species may be present in your trees if you are experiencing problems. As mentioned, keeping trees healthy to begin with is the best option for pest prevention.

Fact Sheet - Bark Beetle