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| Welcome to our tree column, “Ask your local arborist.” Each month, arborists from the Davey Tree Expert Company in Menlo Park discuss a tree-related topic from general care and planting tips to how trees can impact your property. If you have a tree-related question or an idea for a topic to discuss, email lifestyle@embarcaderopublishing.com or post in the comments section at the end of this column. |
Small, but destructive, bark beetles are quietly putting stress on Peninsula oaks and pines. Early detection of this group of insects that tunnel and reproduce under the bark of trees can mean the difference between saving an iconic tree or losing it.
Beetles to watch
Invasive Shot Hole Borer
Barely bigger than a sesame seed, this non-native beetle was first detected in Santa Clara and San Mateo counties last fall and poses an imminent threat to the region’s urban landscapes and natural forests. Unlike others, the Shot Hole Borer attacks healthy native trees. By boring into trunks and introducing a fungus, it causes a slow decline that can eventually kill whole trees. Known hosts include box elder, California sycamore, valley oak, coast live oak, California buckeye, Japanese maple, avocado, acacia and many more.
Oak Ambrosia & Western Oak Bark beetles
These beetles target stressed or weakened oaks such as valley oak and coast live oak. Look for tiny holes and frass: whitish dust for ambrosia, reddish for Western Oak bark beetles. Their tunneling disrupts water flow, leading to dead limbs or tree decline.
Red Turpentine Beetle
The largest North American bark beetle attacks pines, leaving pinkish-brown pitch tubes at the trunk base. It’s less aggressive but signals underlying tree stress.
Tips to keep your trees safe
Look for warning signs: Look for early warning signs: Watch for fine sawdust or frass, resin oozing, yellowing foliage and tiny round holes.
Keep trees healthy: Water deeply during dry spells, mulch to protect roots and limit injuries to trunks and soil that can invite infestation.
Prune strategically: Remove damaged or dead limbs during cooler months to reduce beetle breeding habitat and reduce beetle pressure. For ambrosia beetles, focus pruning in fall or winter when the beetles overwinter in sapwood.
Act quickly: If infestations are advanced, removal may be necessary to protect neighboring trees. Early detection is the best defense.
George Reno is a local arborist at The Davey Tree Expert Company in Menlo Park, which serves communities on the Peninsula, including Menlo Park, Atherton, Palo Alto and Redwood City. Reno can be reached at 866-923-5658.
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