Biology and management of the Pacific flatheaded borer in hazelnuts

The continued shift in the hazelnut industry from eastern filbert blight-susceptible orchards to new resistant varieties has resulted in the planting of thousands of new acres, providing an opportunity for the Pacific Flatheaded Borer (PFB, Chrysobothris mali, Coleoptera: Buprestidae) to cause major problems to these new plantings. Recent dry, hot summers, suboptimal planting sites, and poor management have contributed to the problem. The literature suggests that PFB, like other flatheaded borers, are attracted to the stress signals emitted by establishing and struggling young trees. Female borers find vulnerabilities in the bark to lay their eggs. Larvae hatch, burrow into the tree, and feed on the cambium layer leading to girdling and loss of transpiration, and ultimately cause dieback or death of the tree. Trees that survive initial borer attacks can be severely weakened and risk future trunk failure due to wind or nut load. Inadequate knowledge of PFB has resulted in devastating crop losses for some growers. Cultural practices that reduce tree stress can be preventative measures against PFB, however, many new plantings are treated with insecticides. The timing of insecticide applications is integral to their efficacy. From 2017 through 2020 we’ve followed PFB phenology to create an emergence curve and have implemented multiple plant protection trials to test their efficacy against PFB.