Citrus Infestation: Look Out for Invasive Tiny Beetles

Tiny beetles that have killed tens of thousands of trees in Southern California, recently were found and identified in Santa Barbara County. Known as invasive shothole borers, the beetles tunnel into trees and introduce a fungus that serves as the food source for adult beetles and their larva. As the fungus spreads in the tree, it disrupts the flow of water and nutrients, leading to tree decline, branch dieback, and tree death.

While they seem to prefer box elder, sycamore and willow, invasive shothole borers attack a wide variety of trees and can live and reproduce in more than 65 tree species found in California. They could be infesting trees in your neighborhood without you even knowing it.

What to look for? The main sign of infestation is the presence of small, perfectly round entry holes (about the size of the tip of a medium ballpoint pen), often associated with staining; gumming; sugar-like buildup; and/or boring dust. Dead branches with wilting leaves may be a sign of severe infestation. Look for these signs on trees in your yard and neighborhood. Light to moderately infested trees can usually be managed with branch removals and ongoing monitoring, while heavier infestations may require treatments. Unfortunately, severely infested trees rarely survive, can quickly become hazardous, and are a big source of beetles, so they need to be removed. Proper disposal of green waste including chipping infested wood is a critical step in effective management to prevent the spread of this pest.

With the help of a grant from Cal-Fire, the County Agricultural Commissioner’s Office has identified invasive shothole borers in Montecito and the Santa Ynez Valley, and it has begun removing the most seriously infested trees on county lands. The department is assisting other jurisdictions and the public with ISHB identification, trapping, visual surveys and resources to manage the ISHB. 

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Top right photo: Beetle infestation in castor bean by Akif Eskalen of UC, Davis

Entry hole in a sycamore, photo by Monica Dimson of UC Cooperative Extension

Tree removal in Santa Barbara County, photo by Randall Oliver, UC Statewide IPM Program