Bark Beetle Outbreak—Frequently Asked Questions

Much of the Southwestern Region has periodically experienced severe drought conditions for the past two decades, causing our forests to experience elevated water stress. As a result, several native bark beetles species attacked these drought-stressed trees, leading to elevated widespread tree mortality. For the most current information on bark beetle activity see our conditions report on the Publications page.

Yes, but this may take some time, because trees depend on moisture to fight off beetle attacks. Because beetle populations are so high and geographically widespread, bark beetles have, in essence, a huge head start. In order for beetle populations to dwindle to normal levels across millions of acres, sufficient moisture over an extended period of time will be required.

Applying an insecticide to the bark prior to beetle attack can protect individual trees. This type of treatment will protect trees for about a year. However, it is important to know once a tree is infested it is too late to consider the use of insecticides. The use of systemic insecticides (those injected into the tree) is not recommended for protection of individual trees. Large-scale application of insecticides is not feasible from either an economic, environmental, or practical standpoint. Aerial spraying is not viable as an alternative because the insecticide would not adequately cover the bark surface. In all cases, certified pesticide applicators should be consulted prior to any spraying.

Within 3 to 6 months after a tree dies, its needles will drop to the ground. The snag (a standing dead tree) will stand for a while, usually between 2 and 6 years before falling to the ground. How long a snag remains standing depends on a number of factors, but especially on the rate of decay of the tree's root system. Dead trees could pose a hazard if the path of their fall threatens structures or areas frequented by people.

These native bark beetles are always present in our southwestern forest ecosystems, but usually at low population levels.

Bark beetles chew their way through the outer bark of a tree and feed on the nutritious soft inner bark. After attack, they emit a chemical scent (called a pheromone) that attracts other beetles. The beetles then mate and lay eggs in galleries or chambers they construct between the bark and the wood. A “blue stain” fungus carried by the beetles contributes to the death of tree by clogging water-conducting tissues. Healthy or trees not stressed due to drought conditions can usually ‘fight’ off these beetles by excreting pitch to push the beetles out of the bark.

Because the current bark beetle activity is largely driven by severe drought, there is little that the USDA Forest Service or anyone can do to stop mortality from occurring across the landscape. However, assessments of the situation are being conducted on affected lands and trends in tree mortality are being monitored.

If we look at the bark beetle epidemic at the “Big Picture” scale, the recipe for future success requires thinning of unhealthy forests to restore their ability to naturally withstand these events, even in extreme drought years.

That depends on a handful of factors. For example, if a landowner can afford to, they could treat individual trees with insecticides to prevent future bark beetle attacks. Or, another strategy is to water trees to bolster their natural defenses. (Watering is no guarantee of protection, because a mass attack of bark beetles can overwhelm even a healthy, thriving tree and kill it.)

Another way to protect small groups of trees is to thin the smaller and less healthy trees in the group to give the remaining trees a better chance to regain enough vigor to fight off beetle attacks. Do not perform thinning unless slash can be removed, burned or chipped and dried (see following question). Thinning is the best long-term strategy for preventing bark beetle attacks and will also help to reduce fire danger on private property.

Do not do anything that will introduce further stress to your trees. For instance, anytime a tree is damaged and must produce sap to cope with an injury, it has to expend precious moisture (in the form of sap). That weakens the tree and makes it that much more susceptible to bark beetle attack.

Removing small or poorly competing trees can improve the vigor of the remaining trees. It is a mistake, however, to fail to deal with residual slash from cutting trees (any parts of the tree that have a 3 inch or larger diameter, such as the trunks and limbs). Untreated slash left on the site is actually an attractant to additional beetles. If beetles breed in the slash, they represent yet another source of new beetles to attack the remaining trees. Stacking or piling firewood near uninfested healthy trees can expose these trees to beetles emerging from firewood and should be avoided.

Because feeding on conifer trees by the non-lethal bark moth or pitch nodule moth can resemble bark beetle attack, do not cut down trees before confirming bark beetle presence.  For more information on signs of bark beetle attack see the bark beetle section of our online field guide.

It is difficult to measure the social, environmental and economic impacts related to tree losses due to the bark beetle outbreaks. The duration and extent of an outbreak cannot be predicted, and not all impacts will be negative. Potentially positive results will be the natural thinning of some forests, improved watershed health, improved wildlife habitat, and enhanced biological diversity. Trees reproduce and die throughout the life of the forest; in this event, though, the process of trees dying is far more apparent. Even under the worst circumstances that can be envisioned, there will still be a forest; it just may not resemble the forest with which we are now familiar.

While we know that bark beetles have been a part of the natural ecology of the forests in the Southwestern Region for as long as our forests have existed, early reports often don't provide many details. We know outbreaks have occurred somewhere within the Region in almost every decade since 1950s, but historic records often do not detail specific locations or severity. We cannot predict the duration of outbreaks or how many trees will ultimately die. However, forest tree densities are believed to be well beyond the natural range of historic variability, so tree losses could potentially be greater than previously experienced.

It is generally accepted by the scientific community that many forest management policies and practices contributed to the unnatural tree densities that now exist in our forests. Fire prevention and suppression activities appear to be the primary factors interrupting the natural fire return cycle. Fire suppression during the first three-quarters of the 20th century was intended to protect forests from a perceived "enemy" but it only succeeded in making our forests more susceptible to severe wildfires in the final quarter-century to today. In addition, the increased tree density leads to greater inter-tree competition for limited resources, such as water, resulting in decreased tree defenses against bark beetles. Again, it is important to point out that the current outbreak is largely driven by the severe drought occurring throughout the area.

No federal funds are directly available to private landowners for bark beetle prevention thinning. However some communities are participating with Arizona and New Mexico State Forestry Divisions in fuels reduction programs that could have a secondary benefit in reducing bark beetle susceptibility where thinning achieves improved vigor in the remaining trees. Community assistance grants of this type are generally announced in the local media and are posted on state websites.

Salvage options are considered on a case-by-case basis, but due to economic and administrative limitations, very little of the affected timber would likely be salvaged within the short time-period it remains solid (before rot sets in). Removal of dead trees vacated by beetles will have no impact on bark beetle populations. The situation on affected lands and trends in tree mortality are being monitored, and the National Forests are paying special attention to forest conditions in and adjacent to recreation and highly used area.

Many people are concerned that numerous standing dead trees will contribute to the fire situation. However, the situation isn't as bad as it seems. Typically, beetle-killed trees shed their needles within a few months of dying, so they won't create as big a threat to massive fire spread as one might imagine. The new snags do present a threat of spotting when a forest fire is burning around them, and that threat will have to be considered every time a fire is burning near beetle-killed trees. However, fires burning in this type of forest (snags and dead trees on the ground) do not usually pose a danger to adjacent lands. A fire burning in larger trees lying on the ground would burn longer and hotter, possibly damaging soils and adversely affecting the site in the long-term.

In Arizona, private landowners should contact the local county extension agent or the local AZ State District Forester and AZ State Fire Management Officer.

In New Mexico, private landowners should contact the NM State Forest Health Specialist: