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The shothole borer is a small beetle that can kill an entire tree by boring round holes the size of the tip of a ballpoint pen into a tree’s bark. A beetle is shown in an entry hole above. Photo by Monica Dimson, courtesy UC Cooperative Extension.
UPDATE: The shothole borer has been confirmed for the first time in San Mateo County. The invasive beetle was found in the Redwood Shores community, the San Mateo County Department of Agriculture/Weights and Measures said Friday, Nov. 8, on its website.
Do you have a gardening question? The UC Master Gardeners of Santa Clara County can help. Our volunteers are part of the University of California’s Cooperative Extension program and we are trained to use research-based information to educate our fellow residents on sustainable gardening and landscaping practices specifically for our area.
Our monthly “Ask a Master Gardener” column will answer your questions and offer tips. Have a question? Email lifestyle@embarcaderopublishing.com.
After years of destroying trees in Southern California, the highly destructive shothole borer has arrived in Santa Clara County, posing an imminent threat to trees commonly found in urban landscapes and natural forests. No bigger than a sesame seed, the beetles tunnel into trees and introduce a fungus that they use as their food source. As the fungus grows, it causes a disease that kills branches or entire trees.
Researchers have confirmed that the non-native pest is capable of killing several species of trees, including the box elder, California sycamore, valley oak, Japanese maple and American sweet gum. Dozens of other tree and shrub species are known to host the invasive beetle, such as the California buckeye, coast live oak, avocado and acacia.
Although it’s too late to probably get rid of the invasive shothole borer at this point, it is possible to contain the infestation and protect as many trees as possible, the County of Santa Clara said in a press release.
The County’s Division of Agriculture is asking residents and property owners to be on the lookout for signs of invasive shothole borer infestations.
According to the County, the easiest way to identify an infested tree is an entry or exit hole that is perfectly round and roughly the size of the tip of a ballpoint pen. Other signs include wet staining, gumming (thick resin or sap produced by the tree), frass (insect waste), boring dust and sugary buildup around entry and exit holes.
If you see any of these signs on trees on your property, contact the Division of Agriculture at scc.agriculture@cep.sccgov.org or 408-918-4610. Division biologists can help confirm whether the invasive insect is present.
The County warns not to move or throw away infested branches or logs unless you have taken proper steps to sanitize the wood in consultation with an arborist.
This video describes the problem and how to mitigate the threat.
November gardening tips
Prepare for first-frost date
We’re lucky to live in the Peninsula’s mild winters but we still get frost when it’s really cold. The approximate first and last frost dates for the region, depending on your location, are Nov.15 and March 15. These are important dates for gardeners to remember.
First frost date — This is the earliest date you should expect frost to occur. If you have plants that need to be brought in for the winter, or crops you need to pick before frost, this date will be important to you. When there’s a threat of frost, make sure your frost-tender plants are well-watered. Soil that is damp can hold more heat than soil that is dry. According to the UC publication on the Principles of Frost Protection, ”When the soil is wet … more heat is stored during daylight for release during the night.”
Last frost date — After this date, you shouldn’t expect any more frosts. It’s generally used as a milestone when pruning frost-sensitive plants (such as citrus, where you don’t want to stimulate delicate new growth until the danger of frost is past).
For our climate, the last frost date is not a reliable metric for when to transplant summer vegetables. Daytime temperatures and soil temperatures are more important. See entries for individual vegetables for specific recommendations.
Also see: Frost — Avoidance and Dealing with Damage
November gardening events
There are several UC Master Gardener gardening events taking place all over the county this month. Here are some of them, with more listed on our events page.
- Nov. 9, Mountain View: Roses – Choosing, Planting, Winter Care and Pruning
- Nov. 10, Santa Clara: Save the Seeds!
- Nov. 16, San Jose: Succulent Holiday Open House and Sale at Martial Cottle Park
- Nov. 16, Sunnyvale: Top Habits of Happy and Successful Gardeners
- Nov. 17, Palo Alto: Climate Change and Your Garden
- Nov. 21, Online: Rat Management
Plant onions
This is a good time to plant onions for nice big bulbs. Onions are biennial plants, which means that they are programmed to go to seed in their second year. If they are planted too early in the year and grow too large before cold weather hits, they can be tricked in the spring into acting as if they are in their second year. This means that they will go to seed soon and put their energy into reproducing themselves rather than into growing large bulbs.
Ideally, onion stems should be no bigger than the thickness of a pencil when the cold weather causes them to go dormant. Plant onions from seeds if earlier in the fall or transplants if later. They do best in moist, well-drained soil. Harvest bulbs in the summer when the tops die back.
You can plant green onions at any time and harvest them whenever they are about a quarter to half inch in diameter. Learn more about growing onions including which varieties do well in Santa Clara County here.
Plant wildflowers now for spring bloom
Native California wildflowers herald the beginning of spring – and the time to plant them is now. Besides their showy display, they’re a habitat for local pollinators and a great way to cover up bare spots. If that’s not enough, they also require little care. Just select a well-drained and sunny site, remove weeds and lightly rake the surface of the soil. Hand-disperse seeds and lightly cover with soil, no more than about ¼ inch. Gently tamp them down with the back of a rake and water. After that, let Mother Nature take its course.
Do you want to ask a UC Master Gardener about a plant problem? Submit questions to our Help Desk online.
You can also subscribe to our monthly Tips and Events newsletter. San Mateo residents can also find gardening advice on the UC Master Gardeners of San Mateo and San Francisco website.
