Mountain Pine Beetle- Browning Needles

A bark beetle that destroys the cambium and introduces the blue stain fungus in Ponderosa, Lodgepole, Scotch and Limber pine trees. It is fatal to most trees when attacks are successful.

Identification

The beetle itself is small, about 1/8 to 1/3″ in length, and brown to black in color. They have wings as adults and fly from tree to tree. The noticeable symptom is the pine tree turns brown. Upon closer examination, the browning tree will have “popcorn-like” yellow mounds of sap jutting from the trees bark. These are also called “hits” or “pitch tubes.” The tree is literally pitching the beetles out using sap that flows out profusely when the cambium is damaged. It can be very effective in repelling successful attacks.

Life Cycle

MPB hatch inside of host trees as larvae that tunnel horizontally out from the mothers vertical chamber and feed in the phloem. They overwinter in the larval stage. As winter ends they continue to tunnel and feed before entering the pupal stage. Adult beetles emerge and fly to another host tree guided by pheromones released from other beetles and the trees themselves. When they find a suitable host they drill in through the bark and create a vertical chamber in the phloem. Individuals die shortly after laying eggs.

Damage

Trees that are “successfully” attacked will not survive. A successful attack implies that one or more beetles have penetrated into the phloem and laid eggs. When this happens they commonly vector the blue stain fungus which rapidly spreads through the trees cambium and chokes the vascular system inhibiting water and nutrient flow, which is fatal. The only exception is Scotch pines. Only since about 2005 have they become targets of MPB. Since then the number of Scotch pine attacked by MPB has been growing at an alarming rate. The good news is that they tend to withstand a number of hits over several years without absolute death. Many do die, but proper care will often keep mortality in check for some time.

Management

Conventional

A pesticide spray of either carbaryl or permethrin is the most tested and effective protection from MPB.

Pheromone (Non-Toxic)

This is an approach that can be effective under the right circumstances. The basic idea is that a scent (Verbenone) is released which signals the beetle that a tree (or an area) is tapped out and the beetle then turns its attention toward or a more favorable host.

The results are mixed. It seems that is fairly effective where beetle populations are low to moderate. It has no effect where populations are high to epidemic. Much of the Rocky Mountains are experiencing epidemics.

For high value trees (a tree you just can’t live without) we recommend spraying permethrin even if you are using the pheromone treatment on your property.

Cultural Practices:

The most important part of all tree care starts with cultural practices. As it relates to MPB, here is a list:

Water: Trees need water! Regardless of the season, trees need water. If it is dry out make sure the trees are getting supplemental water from a hose, irrigation system or hire a commercial company to come do it for you. Remember, just because it snows doesn’t mean there is enough water getting to the tree roots. Dig down a few inches and feel the soil. If it doesn’t stick together, then water is needed. If it is too squishy and dripping when you squeeze it then there might be too much water and it’s time to back off.

Fertilize: Many of our landscape trees do not get enough nutrients and minerals from the native soils. Consider getting on a fertilizer program, or do your homework and apply it yourself.

Remove fresh kills: MPB attacks trees in the summer (typically) which can be seen by the pitch tubes formed by the trees reaction to these attacks. Not all attacks are successful. The pitch tubes are an effective way for the tree to “pitch” the beetles out before they actually get in and harm the tree. When an attack is successful the tree will turn reddish sometime between mid fall and mid winter. These trees must be removed before April so that the overwintering larvae don’t have an opportunity to exit the tree and fly to a new tree and start the cycle again. Not only should the trees be removed but they should be disposed of properly. This means all trunk wood needs to be burned (before April!), chipped, buried (landfill), milled and the bark chipped (before April), or wrapped in plastic (tightly!). This is no joke. These beetles have been spread far and wide through firewood and logging projects.

Solar treatments can also be done. This involves heating the trees to a temperature of at least 111 degrees F under the bark. It is very labor intensive.

Thinning: Trees should be spaced properly so that they ample access to soil, water and light. When the forest is too thick, trees are competing for limited resources and many end up stressed. Have a professional make recommendations for your property.

Other Important Issues

Some other issues to consider as a tree owner are Ips Beetle, other engraver beetles, twig borers and Zimmerman Moth. For the purpose of protecting the majority of lodgepole and ponderosa pines along the lower foothills of Colorado, we are mainly concerned with Ips Beetle, which will kill trees in a hurry if attacked. The main difference when managing Ips is timing. While MPB has one generation per year the Ips can have as many as 7. They fly as early as late March and as late as November. This requires two trunk sprays timed early April and again in mid July to early August in order to appropriately protect trees.

What does this mean for you and your trees?

If you are concerned about Ips, we advise two trunk sprays timed in April and late July for your pines. If you have not seen and are not concerned about Ips in your area then once annually, mid April through mid June, will suffice.