Search

Whitebark pine, Pinus albicaulis Engelm. is a subalpine tree endemic to western North America. This species provides multiple ecosystem services and is suffering widespread mortality from mountain pine beetle, Dendroctonus ponderosae Hopkins. Verbenone is a pheromone produced as D. ponderosae feed, and high air concentrations of verbenone deter D. ponderosae from colonizing trees. Synthetic verbenone has been formulated into products used to prevent D. ponderosae from colonizing trees. We compared the ability of verbenone pouches and SPLAT Verb to protect individuals and small stands of P. albicaulis. With individual trees in Montana, all treated trees survived regardless of verbenone formulation and rate, whereas untreated trees suffered 70 and 90% mortality in 2015 and 2016. In plot experiments in California from 2015 to 2017, and Oregon from 2015 to 2018, verbenone was applied to trees spaced ~10 m apart, and survival of small (12.7–23 cm DBH = diameter at 1.37 m height), medium (23.1–33 cm DBH) and large (>33 cm DBH) trees was compared. In California, where >80% of untreated trees survived, pouches increased survival ~2 to 3% and SPLAT Verb increased survival ~4 to 7% regardless of tree size. In Oregon, verbenone pouches and SPLAT Verb performed similarly on medium and small trees, but large trees had greater survival when treated with SPLAT Verb (~93%) than pouches (~82%). Compared to verbenone pouches, SPLAT Verb appears to better protect P. albicaulis from D. ponderosae. [ABSTRACT FROM AUTHOR]

Several formulations of the antiaggregation pheromone verbenone (4,6,6-trimethylbicyclo [3.1.1]hept-3-en-2-one) are registered to protect pine trees and forest stands from mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), but failures in efficacy are not uncommon. In 2011–2013, a novel formulation of (−)-verbenone was developed (SPLAT® Verb, 10.0% (−)-verbenone by weight, EPA Reg. No. 80286−20, ISCA Technologies Inc., Riverside, CA, USA) for protecting individual lodgepole pine, Pinus contorta Dougl. ex Loud., and small stands of P. contorta from mortality attributed to D. ponderosae. We evaluated the efficacy of lower doses of SPLAT® Verb than previously considered for tree protection on the Beaverhead-Deerlodge National Forest, Montana, USA, 2014–2015. In an individual tree study, D. ponderosae pressure was not sufficient to adequately challenge the treatments as only 56.7% of the untreated controls died. However, if one additional tree in the untreated control had died, all verbenone treatments (30 g, 50 g, and 70 g of SPLAT® Verb/tree, and one 7-g verbenone pouch/tree) would have been considered efficacious. In a small-scale stand study, fewer P. contorta were colonized by D. ponderosae on 0.41-ha experimental plots treated with 2.5 kg and 3.5 kg of SPLAT® Verb [250 g and 350 g of (−)-verbenone, respectively] and the 7-g verbenone pouch [50 pouches/plot, 350.0 g of (−)-verbenone/plot] compared to the untreated control. No significant difference was observed between 1.5 kg of SPLAT® Verb [150 g of (−)-verbenone] and the untreated control. Fewer P. contorta were killed by D. ponderosae on experimental plots treated with 1.5 kg, 2.5 kg and 3.5 kg of SPLAT® Verb and the verbenone pouch compared to the untreated control. No other significant differences were observed among treatments. Collectively, these data suggest that lower doses of SPLAT® Verb can be used for tree protection than previously considered, and at a substantial cost savings that could make this strategy economically viable for area-wide management of D. ponderosae. • The anti-aggregation pheromone verbenone is used for tree protection. • SPLAT® Verb is a relatively new product containing verbenone. • Several doses of SPLAT® Verb were evaluated against mountain pine beetle. • Lower doses can be used than previously considered resulting in substantial cost savings. [ABSTRACT FROM AUTHOR]