The Q&A Archives: Pine tree troubles

Question: I have six eight-year-old Monterey pine trees whose needles are turning brown, and I notice many small, round holes in the bark. What's causing this problem and how do I solve it? John Lyle Walnut Creek, CA

Answer: The California five-spined bark beetle (Ips papaconfusus) is the culprit, says David Wood, a forest entomologist who has studied the bark beetle for 35 years at the University of California, Berkeley. Walnut Creek is outside the native coastal range of Monterey pines, and the hot summers and cold winters there stress the trees. Once a bark beetle finds a stressed Monterey pine, the tree is usually dead within a year, notes Wood. Bark beetles are active year-round in California. The adult males drill 1-millimeter-diameter holes in pine tree trunks and emit a pheromone that attracts female beetles, which lay eggs under the bark of the tree. The larvae tunnel under the bark, forming characteristic galleries. Both adults and larvae are thought to carry a fungus that clogs the tree's conductive tissue, causing the tree to die. Once your tree is home to the bark beetles, there is little you can do to stop the infestation. If your pine needles are red, lime-green or yellow and you notice the holes, you might as well cut the tree down - it will die soon, says Wood. The best solution is to grow similar pines that are better adapted to the heat and cold of Walnut Creek and not so susceptible to bark beetle. Good choices are Canary Island pine, Allepo pine and Italian stone pine, he notes. If you have Monterey pines that are not yet infected, keep the trees well watered and only prune between November and February, when the beetles are less active. Tree pruning attracts the beetles, explains Wood.

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