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New Pest Killing California Oak Trees

The Mediterranean oak borer (Xyleborus monographus), or MOB, is an invasive ambrosia beetle that was first collected from declining oak trees near Calistoga in 2019. MOB attacks declining or stressed trees.
There is no effective treatment or cure. Infested trees need to be removed, chipped or solarized.

Pruning the infested limbs may save the tree but typically, once decline is observed, the beetle has moved throughout the tree.  No chemical treatment has found to be effective yet.

MOB moves in firewood. Infested firewood has moved the pest to Lake, Sonoma and Sacramento counties. MOBs host trees are Valley oak (Quercus lobata), which is MOB’s favorite, then to a lesser extent Blue oak (Q. douglasii), and Oregon oak (Q. garryana).

MOB is native to the Mediterranean regions of Europe, the Middle East and North Africa. There, MOB only attacks dead or dying oak trees. Live oak trees in Europe are not attacked by MOB, which was likely introduced to North America in infested wood material. Click here for more information on MOB.