New avocado pest emerges, prompting further research

Avocado growers and urban landscape managers say they're concerned about a newly identified pest that attacks oak and avocado trees.

The California Avocado Commission and other groups are supporting research to determine the extent of infestation by an ambrosia beetle and find appropriate strategies for controlling the pest and the fungal disease it spreads.

Scientists from the United States and other countries who work on ambrosia beetles and the fusarium fungi were scheduled to present ideas for managing the situation at meetings this week at the University of California, Riverside.

The discussions covered what is known about infestations by the previously unknown beetle, now tentatively named "polyphagous shot-hole borer." UCR said the beetle bores into the trees and spreads a fungus that, in turn, attacks the vascular tissue of the tree and disrupts water and nutrient flow.

The species was discovered in Los Angeles County in February and March, and initially identified as tea shot-hole borer, which is native to South Asia, including Sri Lanka, Indonesia and India.

The ambrosia beetle has been detected in the county west of Highway 57 and in neighboring Orange County, as well. In the infested area, reports are coming in about impending tree losses at the Los Angeles Arboretum and the Huntington Botanical Gardens due to the beetle and related fungus infections.

While the infestation survey is not complete, UCR researcher Akif Eskalen said field crews are starting to find the borders of the pest's advance. The area east of Highway 57 appears to be clear of the pest. South of the highway, however, infestations have been found, particularly in parts of Fullerton, Anaheim and Laguna Beach.

So far the Irvine area, which has commercial avocado groves, appears to be free of the beetle. The northern and western boundaries of the infestation appear to be within Los Angeles County.

Although there is a suspected pest find in downtown San Diego, researchers said the county, the nation's top avocado producing area, appears clear of the pest. Ventura County, which also is a leading avocado producer, likewise has shown no sign of infestation.

Surveys continue and experts said once the infestation boundaries are confirmed, it will be easier to monitor the spread of the beetle and infected plants. In July, the avocado commission's executive committee voted unanimously to fund additional research into the pest/disease problem.

The commission said in a letter to members that proper identification and effective control methods of the beetle and dieback threat are of "extreme importance to the California avocado industry" and said it plans to provide growers with research results as they become available.

The beetle also attacks coast live oaks, box elders and other trees. Researchers said the pest/fungus complex causes economic damage to avocados in Israel, but many other tree species may also be susceptible to the threat.

Although the beetle was initially misidentified as the tea shot-hole borer, California Avocado Commission research director Jonathan Dixon said subsequent DNA sequencing at UCR revealed the beetle to be a different, but highly similar species.

At this point, Dixon said, no effective solutions for eradicating the beetle have been found.

(Kate Campbell is an assistant editor of Ag Alert. She may be contacted at kcampbell@cfbf.com.)