The names of these tree-destroying bugs are menacing enough — Goldspotted Oak Borer and Invasive Shothole Borer — but the real nightmare is what they’re doing to our urban trees.
“They have killed hundreds of thousands of trees” since these invasive beetles were discovered in Southern California nearly 20 years ago, said Beatriz Nobua-Behrmann, urban forestry and natural resources consultant for the UC Cooperative Extension for Los Angeles and Orange counties. “They basically eradicated all native willows [San Diego County’s] Tijuana River Valley in just one year. We need people who are vigilant.”
The Goldspotted Oak Borer (aka GSOB) has been found in three species of oak trees in Southern California: Canyon Live Oak – the most widespread oak tree in California – Coast Live Oak and California Black Oak. The beetle was discovered in San Diego County in 2004 and likely came to California with firewood from Arizona or Mexico, researchers say. The GSOB larvae feed on the cambium layer under the bark, which is vital to the tree’s health and growth. A large enough infestation will eventually kill the tree.
Researchers believe the invasive shothole burr arrived in wooden pallets or products from Vietnam and/or Taiwan. It was discovered in the Whittier Narrows in 2003 and has been sighted as far south as San Diego County and as far north as Santa Barbara County. He is far less picky than G-SOB bugs. Invasive shothole borers have sickened at least 65 species of SoCal urban trees — such as box elder, maple, willow, sycamore, oak and cottonwood — by infesting them with their main food source, the fusarium fungus. Beetles “farm” the fungus and eventually block the tree’s vascular system, cutting off the flow of water and nutrients, causing dead branches and then the entire tree.
The UC Agriculture and Natural Resources Program includes an introduction to how people can identify infestations with GSOB and invasive blasthole borers and lists the trees most susceptible to the blasthole borers, including native and non-native cultivars. Here are some tips from Nobua-Behrmann:
– Look for trees with diebacks – dead or dying upper branches – as well as tiny holes in the trunk or larger branches and rust-colored patches on the trunk. GSOB bugs make a D-shaped exit hole.
—Trees with light infestations can be pruned or treated with insecticides to kill the beetles, but if they have dead branches and more than 150 exit holes, it’s a good indication that the infestation may be too severe to treat. In this case, it is best to fell the tree or at least remove the dead branches.
—Immediately chop or burn infected wood to kill the bugs. Do not save infected wood for your fireplace.
— Do not spray your tree with insecticides to prevent infestation. Effective insecticides require a permit for use, and “we don’t want to spray insecticides into the environment unless you have an active infestation.”
— Call your county cooperative office, master gardener program, or agriculture commissioner’s office, or consult this list of certified arborists provided by the International Society of Arboriculture at treesaregood.org.
https://www.latimes.com/lifestyle/story/2022-02-23/how-to-protect-your-trees-from-invasive-beetles How to protect your trees from invasive bugs that kill urban forests