MCH Douglas-Fir & Spruce Beetle Repellent helps protect your Fir & Spruce trees.

Normally, Douglas-fir beetles only breed in felled, injured or diseased trees, In hot and dry summers, they can multiply quickly, breeding in slash, stumps, windthrow, and trees weakened by fire, drought, defoliation or disease. Populations expand rapidly in such material and in subsequent generations beetles attack and kill surrounding green trees.

Outbreaks typically start in the damaged areas and often follow devastation caused by Mountain PIne Beetles after the pine beetles have left. Use MCH in these areas to prevent a population build. If not prevented, the Douglas-Fir Beetle population can "explode", attacking and subsequently killing healthy standing Firs.

In the winter, infested trees are often easily identified by the abundance of bark flakes on the snow, which is evidence of feeding activity by woodpeckers.

In Spring, the newly hatched adults leave the tree of their metamorphosis, seeking out larger trees (usually over 8" diameter if possible) in the surrounding area. (In areas with heavy infestation, beetle hatchlings may take even smaller trees as pressure to get ANY tree increases). When the adults arrive, they begin tunnelling under the bark, lay eggs, which turn to larvae and live through the winter to produce more egg-laying adults to attack more trees. The larvae feed under the bark in the phloem layer, introducing fungi, yeasts, and other organisms that lead to tree death.

Trees attacked early in the Spring may actually produce new adults that will make a 2nd attack in late summer, but the "second flight" usually accounts for less than 10% of the infested trees.

It is estimated that one infested tree will kill at least two and possibly more trees. Thus the exponential devastation occurs.

This is the most important bark beetle on Douglas-fir throughout its range, and it is not easily confused with other beetle attacks on Douglas-Fir trees.

As always, the best defence against Douglas-Fir Beetle is a healthy stand of trees that are able to defend against attack. Proper spacing, basal area, water and removal of brood trees and unhealthy trees are all important.

MCH is widely used by the USFS for preventing attacks on valuable Douglas-Fir stands. Dense stands of large Douglas-Fir trees are at highest risk of attack. If direct control is deemed necessary, trees can be protected using the anti-aggregation pheromone methylcyclohexanone (MCH), which disrupts beetle aggregation. Combining MCH with salvage of infested trees has been successful at reducing subsequent tree mortality.

The patterns of spruce bark beetle infestation over the landscape correlate most strongly with patterns of windfall episodes, and less so with patterns of temperature and precipitation, which makes sense as they prefer downed trees.

USDA notes that "Spruce beetles prefer down spruce to standing trees. On down (windthrown and cut) trees, spruce beetles commonly colonize the lower, well-shaded surfaces and may colonize the entire length of the trunk, typically up to an 8-inch (20-cm) top. In standing trees, beetle activity is most common in the lower 30 ft or so of the trunk... Spruce forest stands most susceptible to attack are located along drainage bottoms. They usually have a canopy comprised of more than 65% spruce."

Higher temperatures will favor beetles reproduction and induce a transition from one to two generations per year in some areas.

Spruce bark beetles are capable of killing trees only when they reach a certain number. Long-term drought and other factors that weaken the trees' resistance are important, because they determine how many beetles are needed to conquer living trees. The number of weakened trees builds up during the interval between outbreaks, and such trees are quickly consumed during an outbreak. Weakened trees thus function as a kind of fuel for the outbreaks.

Spruce beetles may complete their life cycle in 1 year on warm sites at lower elevations or take up to 3 years in cool, well-shaded locations on north slopes. However, throughout most of its range and in most seasons, two years are generally required for the spruce beetle to complete its life cycle.

Like the Mountain Pine Beetle and the Fir Beetle, females bore into the tree, lay their eggs, and let nature take its course. After the eggs hatch, the spruce beetle larvae spend the winter developing under the bark of their host trees. During the second winter of the 2-year life cycle in standing trees, some beetles overwinter in their pupal sites but the majority, often as high as 95 percent, of the new adults emerge, move to the base of the tree, and bore into the bark near the litter line to overwinter. Overwintering at the base of the infested tree reduces predation by woodpeckers and reduces winter mortality due to extreme cold temperatures. There they lye in wait for Spring to emerge as adults.

Although adults may emerge any time from May to October, depending on temperature, most attacks occur in early summer. Dense stands of large Spruce trees are at highest risk of attack. Look for signs from Mid-May thru July and use MCH to repel the beetles starting in early May in most elevations.

Scientists have found that drought negatively affects Engelmann spruce trees, which then have weaker defences against Spruce beetle (Dendroctonus rufipennis), triggering an outbreak in hundreds of thousands of acres in Colorado's forests.

As of 2012, fewer acres of Colorado trees have been affected by spruce beetles than mountain pine beetles, but there are more spruce forests in Colorado than Lodgepole pine, so there's "no reason to expect the percentage mortality to be less or acreage affected to be any less" than it was for the mountain pine beetle epidemic, said Tom Veblen, coauthor of one of the studies and a geography professor at CU.

More than 311,000 acres were killed by spruce beetles in Colorado in 2012, compared to nearly 2 million acres cumulatively by 2018. Infestations seem to be dropping SLIGHTLY in 2019, but are still strong, especially in southern parts of the state like the San Juan and Rio Grande National Forests.

An article published by the Denver Post in October 2017 headline reads "Southwest Colorado forests under attack by pine beetle". Gretchen Fitzgerald, a forester for the U.S. Forest Service’s Columbine District, which manages nearly 700,000 acres of the San Juan National Forest in La Plata and San Juan counties says, "Over the past two decades, more than 120,000 acres of the Weminuche Wilderness — Colorado’s largest designated wilderness area at 488,210 acres — have fallen prey to the destructive spruce beetle."

Spruce beetle continues to spread southward from Colorado, where it has caused extensive spruce mortality - a 55% increase from last year - in New Mexico. Given the heavy spruce beetle activity in southern Colorado, the threat for further massive spruce mortality in New Mexico is high - particularly in the northern half of the state.

As always, the best defence against Spruce Beetle is a healthy stand of trees that are able to defend against attack. Proper spacing, basal area, water and removal of brood trees and unhealthy trees are all important.