by Andrea Sarchet
Madison-Jefferson County Agent
MSU Extension

Many counties in the western region of Montana have been experiencing an outbreak of mountain pine beetle in their forested lands over the last several years. The Mountain Pine Beetle has co-evolved with forested areas of Western North America from central British Columbia to Mexico.  Montana has a long recorded history of MPB outbreaks, including a series of outbreaks from 1925 to 1935 in Idaho and Montana that killed an estimated 1.4 billion lodgepole pines and a vast number of whitebark pines.  The current outbreak in Southwestern Montana began in 2003 and has grown exponentially since.  Not much larger than a grain of rice, this native beetle can devastate large areas of pine forest.  In the forests, this infestation will run its course, but in residential areas and areas in the Wildland-urban interface, steps can be taken to protect high value trees. We do know that the mountain pine beetle infestation will continue for several more years in the surrounding pine forests. If you or your neighbor's shelter belt was attacked in 2009, it is reasonable to think that the surrounding trees are at risk during the summer of 2010.  Prior to taking hasty action in attempts to save trees or prevent the further spread of mountain pine beetle damage, it is essential to be well informed of its biology and management.  Fortunately, we have time to prepare. Following are some important points that will help you in deciding whether or not you should protect your pine trees.

Step 1. Recognize the Signs and Symptoms of MPB Attack.

It is important that you first learn to identify your evergreen trees. This is very simple and can be done by taking a close look at the needles on your evergreen tree. Select one needle and follow the needle down to the base where it is attached to the stem.  If there is more than one needle attached at the same place -it's a pine.  While all species of pine can be attacked, native lodgepole and ponderosa pines are preferred. In some cases, when beetle populations are high, non host trees such as spruces and firs can also be attacked.

Beetles fly in the summer, typically from early July through to the end of August, seeking suitable trees to attack. The first beetles attacking a pine tree emit a chemical odor, (termed an "aggregation pheromone"), that attracts hundreds of more beetles to mass attack and overcome the tree's defenses. During summer and fall watch for pitch tubes that appear on tree trunks. As these tiny beetles chew holes through the bark, the tree exudes pitch that may repel the beetle. Each pitch tube represents a single entrance hole produced by the beetle. From a distance, the stems of mass attacked trees look like they are covered in "popcorn". Also watch for a "ring of sawdust" around the base of pine trees, produced by boring dust pushed out by the beetles as they chew through the bark and construct their galleries.  Galleries can be seen by peeling off a superficial layer of bark with a hatchet. Mountain pine beetles also transport a blue stain fungus that invades the wood, producing the blue streaking that is sometimes seen on pine wood products.  The combined damage caused by the feeding larvae and the blue stain fungus girdles the tree, preventing the flow of water and nutrients, and the tree eventually turns red.

If you see any of these signs of attack on your trees you should assume that your tree is too far gone to save.  If surrounding trees have any of these signs but your trees do not, you should use one of the preventative methods discussed in Step 3.

Step 2. Remove and Destroy Infested Trees.

Infested trees should be destroyed prior to June 15^th, before the beetles emerge as adults.  These trees are a risk to other nearby trees if adult beetles develop successfully and emerge the following year.  Simply cutting the tree down is not enough; the beetles underneath the bark need to be destroyed. Exposing the larvae by debarking the tree, or chipping it, is one method. Other options include burning the wood or burying it under at least 6 inches of soil. Placing tarp over the infested trees or spraying them with insecticide has not been proven to effectively kill the beetles in Montana.

Step 3. Develop a Plan for 2010.

Two preventative options are available to protect pine trees. An insecticide sprayed onto the tree trunk and a repellent chemical odor called Verbenone. In both cases these are preventative, applications need to be made before the beetles fly and attack. The insecticide treatment is very reliable. The repellent works and it is a non toxic alternative, but its effectiveness is more variable.

Based on studies that have been published, Carbaryl is the most effective insecticide.  Carbaryl should be applied once a year prior to the end of June, before beetles begin flying and attacking trees.  Carbaryl is highly toxic to bees that are exposed to direct treatment or residues on blooming crops or weeds.  To reduce the hazard to honey bees apply sprays on days when bees are not foraging.  Always read the product label for more information regarding product restrictions. Applications should be conducted by a licensed pesticide applicator.

Verbenone, a repellent chemical odor, can also be used to protect pine trees.  Verbenone acts as a sort of "no vacancy" signal, mimicking the anti-aggregating pheromone that beetles produce naturally.  Beetles in the area get the message that the tree is full and they should look elsewhere.  Verbenone will soon be available at many local retail locations including hardware stores and Agricultural Supply stores.  Entomologists recommend applying two pouches to each tree prior to July 1.  For areas larger than one acre, pouches should be placed in a grid pattern at 30-45 foot centers, a strategy developed for forest stands.

For more information, please contact Andrea at the Extension Office, 287-3282 or asarchet@montana.edu