Fusarium dieback – invasive shot hole borers (FD-ISHBs) is a serious threat to the viability of the California avocado industry. This emergent ambrosia beetle – associated disease complex from Southeast Asia is formed by two closely related invasive shot hole borer (ISHB) beetle species each associated with specific fungal pathogen species. Specifically, the polyphagous shot hole borer (Euwallacea whitfordiodendrus) carries Fusarium euwallaceae, Graphium euwallaceae and Paracremonium pembeum and Kuroshio shot hole borer (E. kuroshio) carries F. kuroshium and Graphium kuroshium. The broad hosts range has fostered rapid spread throughout urban, ag-wildland forests and many commercial avocado groves in Southern California. Our goal is to develop an integrated pest management (IPM) strategy for the problem. Our objectives are to 1) develop a risk-model for which avocado groves are most vulnerable to FD-ISHB; 2) develop rapid molecular detection methods for the agents; 3) assess the efficacy of preventative and curative chemical, cultural, and biocontrol treatments. In July-November 2017, we established 260 0.25-ha monitoring plots throughout infested and non-infested avocado groves and urban-wildland vegetation. We measured vegetation and landscape characteristics, disease severity, microclimate, and resident beneficial microorganisms across sites. Our preliminary data suggest that xylem-limited bacterial endophytes collected from healthy trees in diseased sites inhibit growth of the fusaria pathogens. Given that the beetles survive by feeding on their fungal symbionts exclusively, microbes interfering with fungal growth thus protect individual plants and present biocontrol opportunities. Our risk model in development will identify areas of spread to help prioritize management efforts to specific sites, avoid unfruitful efforts in low priority sites.

Controlling fusarium dieback: Shot hole borers throughout avocado groves in california

2019 Fall National Meeting

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