The Pine Beetle Epidemic



 We can’t help but worry when we look at our usually green, lush forest and see huge swatches of reddened, dead trees. At the nursery, we get hundreds of inquiries about what can be done to battle the Mountain Pine Beetle (dendroctonus ponderosae) and save existing trees. The answer to this question is complicated, so we’re offering this three part series to 1) help educate homeowners about the Mountain Pine Beetle (MPB), 2) show how to clean up infected/dead trees, and 3) offer advice about how to re-forest the land we love so much. In this article, we’ll look at the history of MPB outbreaks, the life cycle of the beetle, and identification of infected trees.   Historically, the MPB has been a part of the forest life cycle for many thousands of years. During most years, the MPB is hardly noticeable—it’s in its endemic stage where about ½ trees per acres are infected. They live in trees weakened by stress from overcrowding, age, or disease. When those few trees die, the tree stand is opened up to new growth and the dead trees decay and release nutrients into the soil. In fact, they play an important role in keeping forest stands healthy and vigorous. Every ten to twenty years, for unknown reasons and at unpredictable times, the endemic population turns into an outbreak. Without natural barriers, an outbreak can easily become an epidemic.   Residents today expect to see thick stands of trees covering nearly every acre of the mountains, but evidence shows that in pre-settlement times, this was not the case. In fact, spacing before our arrival was merely one tree every 20 feet. Fire prevention has dramatically increased the number of trees today. Foresters estimate that in the past there were 60-100 trees per acre of land. Now, we have 800-1000. This overcrowding weakens the trees as they all have to compete for the same nutrients, sun, and water.  In the past, loss of trees was sporadic, so trees of different ages grew naturally in the forest. Natural fires burned sections of the forest, and the burned trees released seed that grew between old stands. Trees of different ages created barriers to the MPB, keeping them locked in small areas. The beetles would attack only weak trees, killing them and giving rise to new trees. This cycle of death and growth in limited areas kept Colorado forests healthy and strong.  Because of clear-cut mining 120 years or so ago, the re-planted trees are all the same age, allowing the MPB to attack huge swaths of trees. For example, in Keystone in 2001, MPB killed 6 trees. By 2006, that number rose to an alarming 1,154, primarily killing lodgepole pines. In Summit County, it is estimated that infestation has increased 4 fold from 2002-2004. Forest Ranger Rick Newton says that foresters expect 70-80 percent of mature lodgepole pines will perish during this latest outbreak. No one can say for certain why the beetles go into outbreak, but we do know that some of our practices are making the outbreaks worse. Additionally, recent warm weather has allowed more beetles to survive the winter, and these extra beetles attack even more trees. The warmer weather has also allowed beetles to attack trees at higher elevations, where they were previously unsuccessful. Construction injury and road building also create weakened trees that are susceptible to MPB invitations.   


Years of fire suppression, the recent decades of drought, and unusually warm weather have made it possible for Mountain Pine Beetles (MPB) to attack at epidemic levels, even at higher elevations. While the beetle epidemic has marred the beauty of our forests, appearances aren’t the only reason to clean up diseased trees. One diseased tree will infect two or more trees when the beetles fly this summer. While this spread is of great concern, what’s more worrying is the danger of fire. Whether from human error or natural lightening strikes, wildfire will hungrily feed on the highly combustible materials in the forests—and near our homes and properties.  An aerial survey in 2006 showed that over 650,000 acres of Colorado lodgepole pine forests have been attacked by MPB. Keep in mind that an aerial survey doesn’t show infected, green trees—only those that have faded to red. It takes 8-10 months for an infected tree to turn red, so we can assume that many more trees will die and add to the wildfire danger.  Currently, no pesticide can save an infested, mature tree, one 8 inches in diameter or more. A preventative spray for high-value trees may provide some protection, but effectively spraying trees is difficult, very expensive, and must be done yearly. Once MPB infests a tree, it is for all intents and purposes dead. Removal is important so that nearby trees are safe. However, we can actually make MPB worse by removing trees at the wrong time and in the wrong way. Female MPB release a pheromone when they enter the tree that attracts both male and female beetles—it’s the equivalent of ringing a dinner bell at a bed and breakfast hotel. Cutting the tree during this flight time (mid to late summer) spreads the pheromone and attracts even more beetles to nearby trees. Cutting down infected trees must be done before July. Once they are cut, the following methods for disposal of the logs are recommended: §  Burning the logs is 100 percent effective in eliminating the larvae. The logs can be “recycled” as firewood before beetle flight. §  Debarking is also 100 percent effective before July. Removing all of the bark exposes the larvae to killing sun and dries out the phloem, robbing the larvae of their food source. Again, this must be done before flight.  §  Burying the logs at least 8 inches underground and leaving them there until after beetle flight is 100 percent effective. §  Hauling the logs to a “safe site” (at least one mile from any pine trees) is 90 percent effective. Hauling during beetle flight makes it possible for any pine in the travel path to be infected, so hauling must be done before July. §  Chipping the logs is effective if done before beetle flight. §  Finally, if you want to save logs for firewood next year, you can use solar drying, though it is only 50 to 75 percent effective if done correctly. Place the logs in a location that receives several hours of sunlight. Don’t stack the logs. Water them before covering them in clear plastic. Use soil or duct tape to seal the edges and tape any tears. The logs must be sealed in the sun for a minimum of 2 months. These measures will remove unsightly trees and decrease fuel for possible wildfires. In late September, after the beetle flight is over, it is okay to begin cutting again. The logs must be completely dried out (using the methods above) or the beetles will overwinter and emerge next year. Burning the logs as firewood is the best method of removal, as it kills all the beetles and provides an extra source of heat.  Scientists and foresters are not trying to eliminate the MPB. It has always been a natural part of the forest and is beneficial in its own way. It provides food for birds and other insects, it naturally thins stands of old trees, and this allows growth of new, healthier trees. Forests die, and new forests grow in their place—this is a natural cycle that we’ve been interfering with, and it’s possible that our actions have made recent, devastating epidemics possible.  The current epidemic won’t end until we have at least 2 winters of extreme, sustained cold (-40 for several successive days), which kills enough larvae to return the beetle population to its endemic stage. This is what ended the Grand County outbreak in 1984-85. The only other thing that will put the beetles into the endemic stage is their running out of food. In other words, when 80% of their host trees are killed, the epidemic will end. In the meantime, we must do all we can to not make the epidemic worse, and we must work together, or else the efforts of a few will be undone if neighboring properties aren’t also cleaned up. A healthier forest is the key to preventing future outbreaks of epidemic proportions. Sanitation, thinning trees to create healthy stands, selective preventive spraying, and replanting with diversity are the steps we need to take not only to recover from this epidemic but also to have forests in the future that are able to withstand outbreaks. We’ll discuss all of these measures in next week’s article. In the meantime, you can find more information at the Northern Colorado Bark Beetle Cooperative at


As we drive around Summit County, we can’t help but notice all of the orange-taped trees. Most of us have at least a few on our own property. These tagged trees are infested with Mountain Pine Beetle (MPB) and must be removed by July to prevent this year’s beetle flight. Just cutting down a tree won’t stop the beetles from flying. The logs must be burned, buried, debarked, or chipped to effectively kill beetle larvae and pupae. Once all of the infected trees are gone, we’ll see some eyesores where we’re used to seeing lush green forest. We need a responsible plan to replace trees. Diversification of trees, proper spacing, and staggered plantings will ensure that we don’t provide another feast for MPB 80 years down the line.  Forests change all the time. Whether through fire, disease, or pests, old forests die and new ones arise. This cycle occurs over centuries, not decades. MBP will always be part of our forests, so our focus should be on the trees, not the pests. The stronger the tree the better it can protect itself. Nearby trees compete for the same nutrients, sun, and water.This is why diversity and spaced plantings are so important. For example, if a newly cleared swath of infected lodgepole pines is replaced with overcrowded spruce, we’ll have a spruce beetle infestation on our hands in the decades to come. As we replant, we must keep an eye on the future so that we don’t create new problems. At the nursery, we get many calls about the effectiveness of insecticides to stop beetle infestation. Unfortunately, there is no labeled insecticide to battle MPB. Additionally, insecticides are cost prohibitive for large areas, and it is difficult for property owners to apply insecticides completely—from the trunk to the crown. Spraying high value trees with carbaryl (brand name Sevin) may offer some protection. Spray in the spring or early summer, as any application after beetle flight is ineffective. Trees 7 inches in diameter or less need no spraying. They are too small to have enough phloem (what MBP eats) to be likely targets for attack. Homeowners who wish to use a professional for preventative spraying may save money by contacting a company to have many properties in the neighborhood sprayed at the same time. This year, we are introducing a seedling tree program at the nursery. Because the weather has been unseasonably warm for the last few decades, we are introducing different varieties of trees that haven’t succeeded in the county in the past.

  • Bristlecone Pine (Pinus aristata) is a slow growing, shrubby tree with dark gray bark, irregular spreading branches, and dark greed needles. It reaches a height up to 50 feet. It grows just below tree line, likes sun to part shade, and has low water requirements.

  • Limber Pine/Colorado Blue Spruce (Pinus flevilis) has a pyramidical shape, reaches a height of 30 to 50 feet, and smooth gray bark that turns black at maturity. Plant in sun to filtered shade. Limber pine has low water requirements.

  • Douglas Fir (Psuedotsuga menziesii ‘Glauca’) can reach a height of 80 feet, requires medium water, and has downswept branches with bright green needles.

  • Engleman Spruce (Picea englemanni) has top branches what sweep up and bottom branches that sweep downward. Their life span is 300-350 years. They have very thin, gray or purplish-brown bark, and will reach a height of up to 150 feet.

  • Supalpine Fir (Abies lasiocarpa) has a lifespan of 200 years and reaches a height of up to 120 feet. Its branches have blue-green needles at brushed up angles, gray bark that crackles with age, and beautiful purplish cones.

  • Concolor Fir (Abies concolor) is also known as the White Fir. It is recommended by the National Christmas Tree Association for its pyramidical shape, soft, flat green needles, and branches that flow to the ground in a symmetrical outline. It reaches a height of 40 to 60 feet, is sun to shade tolerant, and has medium water requirements.

Seedling trees are very small and need special care for the first few years until they are established. They should be planted as soon as possible after purchase. Choose seedlings that match your planting site, considering height and spread of the mature tree. It may appear that the seedling has plenty of room, but remember that in the next decades it will ruin fences and building foundations if planted too closely. Consider the tree’s soil, water, and sun requirements. Your local nursery will have planting guides and tree descriptions to help you choose wisely. Plant a variety of trees, provide good spacing, and stagger plantings over several years to achieve a healthy, balanced forest of strong trees able to protect themselves from future epidemics. We can think of the pine beetle epidemic as a catastrophic event in the life of the surrounding forest, or we can look at this as an opportunity to create resilient, vigorous forests for our future. Tree growth occurs on a scale of hundreds of years, not just a few decades, and our continuous commitment will help restore the forests that we need and love so much. For more information, contact the Friends of the Dillon Ranger District at,or the Northern Colorado Bark Beetle Cooperative at

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