The Western Poplar Clearwing Moth (WPCM), Paranthrene robiniae (Sessiidae) is the most economically important pest of hybrid poplar in eastern Washington and Oregon. WPCM larvae burrow into poplar trees causing galleries that discolor the heartwood and weaken limbs and trunks to the point of breakage. WPCM are especially damaging to young trees where one larva can cause the death of the tree.

Historically poplars have only been used for high quality paper pulp, but with pulp value dropping, Potlatch® has switched their target product to quality ‘veneer’ logs and WPCM galleries cannot be tolerated.

Chloropyrifos (19,958 kg) failed to control WPCM in 2002. Potlatch® is restricted by guidelines of the Forest Stewardship Council, which prohibits the use of broad-spectrum pesticides. Boise® is not as restricted in their choice of insecticides, but are still very enthusiastic toward a ‘soft’ management strategy.

We received a Section 18, and implemented a pheromone based ‘mating disruption’ strategy in that targeted 3,238 ha of newly planted and one year old trees in 2003 and 10,117 ha of all age trees in 2004. Here we will report our season long trap catch data, the effects of the pheromone treatments, and the results of our damage survey. Membrane dispensers were more effective, but expensive to apply. Flowable formulations of 1.24 g/ha/season effectively suppressed capture.