Assessing thousand cankers disease severity in California

Thousand cankers disease (TCD), which affects walnut trees, has contributed to walnut mortality in the western United States for over a decade. It is caused by the bi-phasic fungus, Geosmithia morbida, and is vectored by the walnut twig beetle (WTB) Pityophthorus juglandis. Although the beetle is native to California, it was not considered a pest until recently, when G. morbida was identified as the causal agent of the deterioration of walnut tree health in California (2008). The interaction between WTB and G. morbida has not yet been fully characterized. Annual walnut tree (Juglans) surveys were conducted at six sites in California (Butte, Los Angeles, Solano, Sutter, Tulare, and Yolo Cos.) for symptoms of WTB and TCD (2009-2011). Sites were chosen to represent various species of Juglans and a range of environments (orchard, urban, and wildland). Geosmithia morbida propagule loads were measured from WTB’s collected in funnel traps in each of the six survey sites (2011). Future annual surveys will reveal trends in walnut species susceptibility, diseased tree life expectancy, and correlations between G. morbida propagule load size/frequency and site disease severity.