Pine beetles, such as the mountain pine beetle and southern pine beetle, are small insects that threaten pine forests and individual trees across North America. These bark beetles bore into the tree’s phloem layer, where they feed and reproduce. This process effectively girdles the tree, disrupting the flow of water and nutrients. Infestations quickly overwhelm a tree’s natural defenses, leading to widespread mortality and creating economic and wildfire hazards. Because beetles coordinate mass attacks using pheromones, rapid intervention is necessary to prevent outbreaks.
Identifying an Active Infestation
Detecting an active infestation early is the most time-sensitive step in protecting surrounding trees. The clearest sign is the presence of pitch tubes, which are small masses of resin the tree extrudes to push the invading beetle out. These tubes can be white, pink, or reddish-brown and are typically found on the lower 15 feet of the trunk.
Another indication is boring dust, known as frass, which the beetles expel from their entry holes. This reddish-brown material collects in bark crevices or accumulates at the base of the trunk. Removing bark may reveal the intricate, winding tunnels or galleries carved by the adult beetles and developing larvae beneath the surface.
The most visible symptom is needle fade, where the crown discolors. Needles transition from green to yellow, and finally to a rust-red color as the tree dies. Blue stain fungus, carried by the beetles, can sometimes be seen as grayish-blue streaks in the sapwood. By the time the needles turn red, the tree is functionally dead, requiring immediate removal for containment.
Proactive Measures for Healthy Trees
The most effective approach to managing pine beetles is prevention, focusing on maintaining tree health and applying protective treatments to high-value trees. Healthy trees possess sufficient sap pressure to “pitch out” the initial attacking beetles, making them naturally more resistant to mass attack. Proper health management includes ensuring adequate watering during drought and avoiding physical damage to the trunk.
In forested areas, thinning crowded pine stands reduces competition for resources like water and sunlight, which increases tree vigor. The goal is to create spacing between crowns, making it harder for beetles to coordinate attacks using pheromone signals. Removing older, less vigorous pines also reduces the pool of susceptible host trees that could start an outbreak.
For individual, high-value trees, a prophylactic chemical application is the most reliable protective measure. These preventative, non-systemic insecticides, such as permethrin or bifenthrin, are sprayed directly onto the trunk bark. The chemical acts as a barrier, killing adult beetles as they attempt to bore into the tree.
Timing is paramount for these bark sprays, which must be applied before the adult beetles begin their annual flight, typically in late spring or early summer. A certified applicator must drench the trunk completely, from the base up to where the diameter tapers. These treatments are not remedial and generally need to be reapplied annually.
Treating and Removing Infested Trees
Once a pine tree is confirmed to be actively infested, the goal shifts from saving the tree to preventing the spread of the infestation. Because the insects reside beneath the bark, protected from topical sprays, the infested tree cannot typically be saved. The established protocol is the immediate felling and destruction of the infested tree before the new generation of adult beetles emerge, usually in mid-summer.
The most common reactive measure is mechanical control, often involving felling the infested tree and a buffer strip of surrounding pines. The “cut-and-remove” method involves taking the felled trees to a mill for immediate processing or destruction. The buffer strip is cut to disrupt the beetle’s pheromone communication system and stop the spot’s growth.
A related tactic is “cut-and-leave,” where the infested and buffer trees are felled but left on site. This method can cause mortality in the beetle brood due to microclimate changes and is used when removal is impossible. The infested material must be destroyed or treated on-site to kill the developing brood before they emerge.
Limited remedial options exist for high-value ornamental trees. Systemic insecticides, such as emamectin benzoate, can be administered via trunk injection to protect the tree for two or more years. Pheromone pouches containing anti-aggregating chemicals like Verbenone can also be deployed to repel incoming beetles, but their effectiveness is variable during a large-scale epidemic.
Safe Disposal and Site Cleanup
After felling an infested tree, the material must be managed immediately to ensure the developing beetle brood is eliminated before adult beetles emerge. Disposal timing is critical, as insects can complete their life cycle under the bark in as little as six weeks. Any material with evidence of infestation must be handled with care.
Methods of Brood Destruction
Several methods exist to eliminate the developing beetle brood:
- Solarization: This involves cutting logs into manageable lengths, stacking them in direct sunlight, and covering the stack with a clear, six-mil thick plastic tarp. The edges must be sealed with soil to trap heat, raising the internal temperature to lethal levels (typically over 120 degrees Fahrenheit). Logs should be left covered for at least three months during the summer.
- Chipping: The infested wood can be chipped into pieces no larger than one inch, a process that mechanically destroys the larvae and pupae.
- Burning: Burning the infested material is an option where local regulations permit, with high-heat methods ensuring the complete destruction of the insects.
- Debarking: For logs intended for use as firewood, complete debarking is viable, as the beetles live and feed only in the phloem layer beneath the bark. Once the bark is removed, the wood is no longer a threat.
After all infested material is removed or treated, the surrounding area should be monitored closely for new signs of attack on adjacent trees following the removal.