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Bark beetles are common pests of many trees. Some of the most damaging attacks occur to pines and other conifers. Trees already stressed by drought, disease, or mechanical damage are most likely to suffer. Insecticide sprays can’t save infested trees. Instead, promptly remove infested trees and protect healthy ones with proper cultural care.
Identifying 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 branches and trunks.
- Infested trunks and branches have many tiny holes where beetles have bored in or emerged.
- Tree sap or dust from boring can exude from holes.
- If you peel back bark on infested trees, you will see galleries, or tunnels, from adult 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, other pines. Shothole borer is common on broadleaf trees.
Bark beetles injure trees by disrupting the flow of nutrients. |
- Adults and larvae feed in the area of the inner bark that transports food through the tree.
- Needles turn yellow and drop off infested trees.
- Infested trees can die in one season, causing limb drop and fire hazards.
Keep trees vigorous to reduce attacks. |
- Healthy trees defend themselves by releasing sap into holes before adult beetles can lay eggs.
- Drought, disease, and injuries reduce a tree’s ability to combat invasions.
- When possible, properly irrigate drought-stressed trees.
- 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.
- Diversify your landscape. Avoid single-species stands.
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Remove severely infested trees. |
- Regularly inspect your trees for signs of bark beetle invasions including dust from boring, small holes exuding sap, and tree decline.
- Promptly remove infested trees and destroy infested material by chipping or solarizing to prevent emerging beetles from attacking healthy trees.
- Solarize infested wood by tightly wrapping small piles in thick (10 mil), clear plastic and leaving them in the sun for several months.
- Protect healthy trees through good cultural care.
Insecticides generally aren’t recommended |
- Chemicals can’t save infested trees.
- Insecticides, including systemics, won’t control insects already inside the tree.
- Chemicals aren’t effective unless applied before adults land on the tree.
- Confine chemical use to protecting healthy, specimen trees and integrate with other methods to improve defense.
- Effective insecticides are available only to licensed applicators.
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| Adult western pine beetle | Galleries of the western pine beetle (left) and engraver beetle (right) |
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. |
