Verbenone (SPLAT® Verb) delays Ips typographus (L.) infestation and reduces infestation risk and severity in windthrown Norway spruce in Southwest Germany

Abstract

Outbreaks of European spruce bark beetle, Ips typographus, often follow storms, and can result in losses of Norway spruce, Picea abies, that largely exceed those caused by storms alone. Management actions to reduce P. abies losses attributed to I. typographus mainly consist of salvage and sanitation logging of windthrown P. abies, which are sometimes limited by logistic capacities and constraints. Recent outbreaks across Europe have destroyed large areas of P. abies forests, and are expected to further intensify as a consequence of climate change, so that additional tools are needed for integrated bark beetle management. In a 4-yr study, we applied (–)-verbenone (SPLAT® Verb, ISCA Inc., Riverside, CA, U.S.), a common bark-beetle inhibitor, to natural and artificially generated windthrows of P. abies (5–6 trees) to examine its efficacy for reducing infestation by I. typographus in spring. In two of four years, SPLAT® Verb caused delay of infestation of ∼3 wks, which may provide a relevant gain of time for logging operations. Infestation probability and density were reduced by up to 78% and 76%, respectively. Treatment effectivity increased with dose per volume of windthrown P. abies and seemed to decrease with greater infestation pressure. Elevated concentrations of verbenone in the active airspace of forests could only be detected in close proximity (<50 cm) of SPLAT® Verb application points (dollops). We propose a decision pathway for management of windthrown P. abies that includes verbenone as an environmentally friendly tool within the integrated management of I. typographus in Central Europe.