Look for tea shot hole borer exit holes in the trunks of avocado trees.
Look for tea shot hole borer exit holes in the trunks of avocado trees.

A minute beetle and the fungus it carries have been linked to branch dieback in residential avocado and landscape trees in Southern California, causing concern for the state's avocado industry.

How widespread the pest complex is is the subject of a survey currently being conducted in Southern California, says Akif Eskalen, an Extension plant pathologist at the University of California, Riverside.

The Irvine-based California Avocado Commission is providing emergency funding for the survey, he says.

So far, surveyors have identified the disease in eight areas of Los Angeles County, including Downey, Whittier, Long Beach, Hacienda Heights and Pico Rivera.

They have yet to find it in a commercial avocado grove, Eskalen says.

Beetle, fungus cause concerns for California avocado growersThe tea shot hole borer is an exotic ambrosia beetle smaller than a sesame seed.

It resembles the redbay ambrosia beetle that is causing problems in Florida avocados but is a different species, Eskalen says.

"They're really not even cousins," he says.

The fungus associated with the tea shot hole borer is a new species of Fusarium that has yet to be named.

The disease it causes is dubbed "Fusarium dieback."

The beetle transmits the fungus as it burrows into trees.

The pathogen reproduces in the tree's xylem—the tissue that carries water and nutrients from plant roots through the trunk to branches.

Eventually, pathogen colonies plug the xylem, causing branches to die.

These symtoms are different from laurel wilt, where the entire tree dies in a short period, Eskalen says.

The tea shot hole borer was first detected in Los Angeles County in 2003. At the time, the establishment history of the beetle-disease complex in the state was not fully known.

In fact, this particular Fusarium species wasn't even known until 2009, when it was first identified infecting Israeli avocados, Eskalen says.

Israeli researchers also identified the tea shot hole borer as the disease vector.

In February, Eskalen said he found the beetle and fungus on a residential avocado tree with branch dieback symptoms in South Gate, Los Angeles County.

The tea shot hole borer has been reported on 18 different plant species worldwide, including avocado, tea, citrus, guava, lychee, mango, persimmon and pomegranate.

It also can fly up to 500 yards, he says.

In Southern California, surveyors have found it on residential avocados and boxelders.

They've also found it on castor beans, "which is good for castor bean control but it also can be a source of inocolum," Eskalen says.

He urges growers to avoid moving firewood or infested plant material to help control the spread of the beetle-fungus complex.

To report sightings of the borer or signs of Fusarium dieback, contact Eskalen at (951) 827-3499 or aeskalen@ucr.edu.