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Pests in Gardens and Landscapes: Quick Tips

California fivespined ips, also called pine engraver. Actual size: 1/8 to 1/4 inch.

Monterey pine killed by engraver beetles.

Egg gallery and larval mines of European elm bark beetle.

Bark beetles are common pests of many trees including conifers and broadleaf trees. Native bark beetles typically attack trees already stressed by drought, disease, or mechanical damage. Newer invasive species can attack and kill healthy trees. Insecticides won’t save heavily infested trees. Instead, promptly remove infested trees and protect healthy ones with proper care.

Identify bark beetles and their damage.

• Adults are small, dark, cylindrical insects about the size of a grain of rice; they can fly from tree to tree.
• Larvae are tiny grubs that feed beneath bark on trunks and branches.
• Infested trunks and branches have many tiny holes where beetles have bored in or emerged. Signs include dust from boring, small holes exuding sap, and tree crown decline.
• If you peel back bark on infested trees, you may see galleries (tunnels) from adult and/or larval mining.
• Bark beetles in California include western pine beetles on ponderosa pine; mountain pine beetles on lodgepole and sugar pines; and engraver beetles on Monterey, pinyon, and other pines.
• Shothole borers and elm bark beetles attack some broadleaf trees.

Bark beetles injure trees by disrupting the flow of nutrients.

• Adults and larvae feed on the inner bark that transports water and nutrients through the tree.
• Needles or leaves turn yellow and drop off from infested trees.
• Infested trees can die in one season, causing limb drop and increased fire hazards.

Keep trees healthy to reduce attacks.

• With low to moderate numbers of beetles, healthy trees defend themselves by releasing sap into holes before female adult beetles can lay eggs.
• Drought, disease, and injuries reduce a tree’s ability to combat invasions.
• Properly irrigate trees to avoid drought stress.
• Thin groups of trees or stands to keep remaining trees vigorous. Dense stands favor beetle attack.
• Avoid compacting soil and injuring roots and trunks during activities such as construction.

Remove severely infested trees.

• Regularly inspect your trees for signs of bark beetle invasions.
• Prune infested branches and dispose of them to reduce beetle populations.
• If the trunk is infested, promptly remove the tree. Destroy infested plant material by immediately chipping or solarizing to prevent emerging beetles from attacking nearby trees.
• Solarize infested wood by tightly wrapping small piles in thick (10 mil) clear plastic and leaving them in the sun for several months.

Bark beetles can be moved to new areas in infested wood. Don’t move firewood.

What about pesticides?

• Insecticides won’t save heavily infested trees because they have limited impact on bark beetles inside the tree.
• Protect healthy trees by applying a systemic insecticide before adult beetles attempt to bore into the bark to lay eggs, and use nonchemical methods to improve tree defense.
• Effective insecticides for bark beetles are available only to licensed applicators.

Minimize the use of pesticides that pollute our waterways. Use nonchemical alternatives or less toxic pesticide products whenever possible. Read product labels carefully and follow instructions on proper use, storage, and disposal.