Spruce Beetles in Alaska: What You Need to Know to Protect Your Trees

Understanding Spruce Beetles and Their Impact on Alaska’s Forests

Beetle Kill Spruce in Eagle River, Alaska October 2024

Spruce beetles are a persistent threat to Alaska’s forests, causing significant tree mortality across the state. While they exist naturally in the environment, their presence often goes unnoticed until large-scale outbreaks occur. Southcentral Alaska has experienced the most severe damage, though these beetles pose risks statewide. Beyond forests, they can also infest ornamental spruce trees in residential and community areas, impacting both natural and urban landscapes.

How Spruce Beetles Attack Trees

Each year, between mid-May and July, adult spruce beetles emerge from infested trees and seek new hosts. They typically target the lower portions of tree trunks, burrowing beneath the bark to reach the phloem—a crucial layer that transports nutrients. Female beetles lay eggs in tunnels within the phloem, and as larvae hatch and feed outward, they disrupt the tree’s ability to transport essential nutrients. If the damage is extensive, the tree eventually dies.

Tree Vulnerability to Spruce Beetles

Spruce beetles primarily attack white, Sitka, and Lutz spruce, while black spruce is rarely affected. They can also infest ornamental varieties, such as Norway, Engelmann, and Colorado blue spruce. Generally, trees over 12 inches in diameter are preferred targets, although smaller trees may also be affected under certain conditions. Older and larger trees are particularly at risk, especially if weakened by drought, injury, or competition.

Recognizing Spruce Beetle Infestation

Beetle Kill Spruce in the Palmer Hay Flats February 2025

Signs of spruce beetle infestation include:

• Boring dust: Fine, reddish-brown sawdust accumulating in bark crevices or at the tree’s base.

• Pitch tubes: Small, resinous formations where beetles have entered the bark, varying in color from creamy white to reddish-brown.

• Needle discoloration: Trees may shift from green to yellow, then to reddish-brown, before shedding needles within a year of infestation.

Strategies for Managing and Preventing Infestation

Healthy trees are more resilient against beetle attacks. Strategies for prevention include regular watering, fertilization, and strategic pruning of lower branches—outside the beetles’ active period (May to July). Removing and processing weakened or infested trees through debarking, chipping, or splitting helps prevent further spread. Firewood storage is also crucial; infested logs should not be kept near healthy spruce trees, as beetles can emerge and infest new hosts.

For high-value trees, insecticides containing carbaryl or permethrin can be applied in early May. Injection treatments with emamectin benzoate or abamectin require precise timing for effectiveness.

Beetle Kill Spruce. Note the horizontal crack caused by wind loading. This tree reached imminent failure within one year.

Ensuring Long-Term Forest Health

Sustaining a healthy and resilient forest requires proactive management. Promoting a diverse mix of tree species and age classes can help reduce future outbreaks. Thinning overcrowded stands enhances tree vigor, while removing dead or infested trees before May can curb beetle spread. Additionally, homeowners should ensure that any spruce firewood they bring onto their property is debarked or stored properly to avoid accidental infestations.

For further assistance, local forestry experts and tree care professionals can provide valuable guidance in managing and mitigating spruce beetle threats effectively.

Protect Your Trees with Polar Tree and Engine Care

If you’re concerned about spruce beetles threatening your property, Polar Tree and Engine Care is here to help! Our team of tree care professionals specializes in beetle prevention, tree health maintenance, and infestation management. We offer expert pruning, tree removal, and insecticide treatments to safeguard your valuable trees. Don’t wait until it’s too late—contact us today to schedule an inspection and take proactive steps to protect your spruce trees!