Bark Beetles


(Courtesy of Sabine Shurter)

We have just had a tree expert coming to our place in La Cueva to assess some trees that we thought have been infested/killed by bark beetles. Turns out they have been infested with borers. He explained that bark beetles will mostly affect pinons/junipers. Most damages to ponderosa pines are caused by borers.

How to Tell the Difference!

A bark beetle infested tree will die within a few weeks (as little as 2 weeks). Bark beetles travel with the wind and go on to the next victim.

Borers will kill a tree very slowly over weeks, maybe months, or not at all. A branch or few branches may turn brown at first and more and more branches go brown. A borer infested tree can be treated with inoculations. Some trees infested with borers will also show some bulging at the bottom of the trunk (which will sag when depressed). But that may be the case or not.

Another interesting piece of information: Individual stands of trees should not be necessarily thinned too much (if they do not present an immediate fire danger). Borers like to go to weaker trees (as strong healthy trees may be able to fend them off by drowning them in their sap ... of course also a function of water supply available to the tree). So if you have nice trees to protect, leaving a few weaker trees may draw the borers to the weaker trees and thus save the trees you would like to keep from being infested.

Bark Beetles

(Facts about Bark Beetles - Before and After Thinning)

Important Warning! Bark Beetles are dangerous and persistent pests even if you cut down all infected trees, and thin your lot. The slash and "firewood" that is left must be treated with great care!

Time of thinning is related to new or continuing beetle attack:

Freshly cut ponderosa pine slash and firewood are subject to attack by bark beetles that emerge in April and May. The success of beetle attacks and production of young beetles are greatly influenced by when trees are cut. Trees cut during the late summer and fall are seldom successfully attacked, because the inner bark dries during the fall and winter. The inner bark of green trees cut from January to July remains moist and suitable for beetle habitat. An exception to this is the roundheaded pine beetle, which flies during the fall, and attacks trees at that time. Roundheaded pine beetle activity is found near trees that have been thinned and chipped in October.

What can you do to limit new or continued beetle attack:

The slash and limbs of green pine trees cut in winter or early spring should be buried, burned, or chipped by mid May, or within 30 days if cut later (beetles, eggs, or larvae cannot live in chips, although some adult beetles might escape a chip pile). The bole of the tree should receive the same treatment, unless it is needed for firewood or poles. Then the material should be piled away from living pine trees and covered securely to the ground with heavy, clear plastic. The plastic covering should be left on the pile at least 60 days if the trees are cut during the April though October period. Heat builds up under the plastic and kills or traps the beetles. This treatment also dries the inner bark limiting the food for the beetles. Trees cut in winter should be used in a fireplace or disposed of before April. If not used, the firewood that is left at the end of March should be covered for 60 days. If logs are to be used as poles they should be pealed as soon as possible.

Use of insecticides is generally not recommended:

There are no practical and effective sprays or injections to stop an attack on green trees. Insecticides are not recommended once bark beetles have successfully attacked. Un-infested trees can be protected from beetle attacks by spraying with insecticides. When spraying, the entire trunk of the tree up to 4" diameter must be covered. This is a protective measure only. Insecticide will not kill beetles once they enter the tree. The available chemicals for this purpose can vary from year to year. You must use a product that is especially formulated for bark beetles. Typical home and garden insecticides will be ineffective. Check with our local county Extension office for current recommendations on the proper insecticides to use as a preventive measure.

Watering increases trees resistance to attack, but.......

Healthy trees offer some resistance to attack. Watering during dry periods (when less than 2 in. of moisture per month occurs) can help keep trees healthy. Thinning out dense stands of trees will make more water available for the remaining trees. Insecticides can be sprayed on the bole of the tree to prevent initial attack by beetles. This must be done prior to beetle emergence in the spring to be effective. A fading crown and boring dust are the surest signs that a live tree has been attacked. When the entire crown begins to fade, there is no hope of saving the tree, and it should be removed as quickly as possible to prevent emerging beetles from attacking other trees. Once the entire crown has turned yellowish brown, it is generally too late to stop the spread because the beetles have already flown to attack nearby trees.