A polyphagous shot hole borer
A polyphagous shot hole borer

An avocado-killing fungus and the beetle that carries it continue to spread in Southern California, having most recently been found in Riverside and San Diego counties.

The polyphagous shot hole borer and Fusarium dieback were first confirmed in residential avocado trees in Los Angeles County in 2012. They then spread to neighboring San Bernardino County.

In Israel where the pest complex also has been found, it has caused severe damage to avocado and related landscape trees since 2009, according to a news release.

Akif Eskalen, a University of California, Riverside, Extension plant pathologist, continues to monitor the situation in Southern California.

The beetle burrows into the tree, carrying the Fusarium fungus in its mouth parts.

As it feeds, it inoculates the tree.

The fungus attacks the vascular tissues within the tree, blocking the transport of water and nutrients from the roots to the canopy.

Eventually, the tree experiences Fusarium dieback and dies.

Beetle larvae live in galleries, or tunnels, within the trees and feed on the fugus.

In addition to avocados, Fusarium dieback has been observed in more than 117 other plant species, including persimmon, olive, boxelder, coast live oak, valley oak, California sycamore, big leaf maple and weeping wildow.

For more information, including what signs to look for, visit Eskalen's website.