Protecting Poplars from a New Pest
When major producers of hybrid poplars in the Pacific Northwest sought help from Washington State University in 2000 to protect their nearly decade-old stands from pests, entomologists John Brown and Doug Walsh started by targeting the usual suspects.
They assumed their research on applying integrated pest management techniques would focus on traditional poplar pests such as the poplar willow borer and the cottonwood leaf beetle.
But in 2002, a new pest emerged as a threat to the poplar stands: the western poplar clearwing moth.
“In 2001, our pheromone-baited traps captured 95 western poplar clearwing moths in a four-week period,” Brown said. “During the same four-week period in 2002, we found more than 18,000 moths in traps placed at the same locations. It clearly was an outbreak.”
According to Brown, the moth larvae burrow through the trees’ cambium layer and into the heartwood, leaving them prone to breakage and blow over, and unusable for saw timber. The pests will girdle the bark on small, newly planted trees, killing them.
With more than 36,000 acres of irrigated poplar at risk in eastern Washington and Oregon—much of it nearing maturity for use as saw timber—the potential economic impact to producers like Potlatch Corp., Boise-Cascade, and Green Wood Resources were substantial.
In an attempt to stem the outbreak in 2002, the producers applied 44,000 pounds of an organophosphate pesticide, Lorsban ®, to no avail. Other contact pesticides applied to control other pests had no effect on the clearwing moth.
To complicate matters, major saw timber retailers, such as Home Depot and Lowe’s, are committed to buying lumber from producers that manage their timber under Forest Stewardship Council guidelines that severely restrict pesticide use. An effective alternative was needed—and quickly.
Brown and Walsh and their integrated pest management (IPM) team recruited Jocelyn Millar at the University of California at Riverside to join them. Years earlier, he had isolated the clearwing moth’s sex pheromone that the team had used in its traps. The pheromone attracts and confuses male moths, thus disrupting their mating cycle. With only a limited supply of the synthetic pheromone available, and approval required by the U.S. Environmental Protection Agency of a Regional Section 18 permit for use of an unregistered pesticide, only one-third of the poplar plantings was treated in 2003.
“We saw some tangible results, and we were able to refine the formulation and application for future years,” Brown said. “We obtained another Section 18 (permit) in 2004 to apply (the synthetic pheromone) to all the stands, which resulted in a significant reduction in clearwing moth damage.”
In 2006, the EPA granted full approval for use of the new pesticide to control the western poplar clearwing moth. The success of the pheromone-based IPM strategy has meant that Lorsban has not been applied on Pacific Northwest hybrid poplar plantations since 2002.
“That’s a 44,000-pound reduction in organophosphate use,” Brown said. “The synthetic pheromone is nontoxic, so workers can re-enter the forest only a few hours after application, and it takes as little as one gram per acre per year to be effective.”
The project’s success resulted in the Entomological Society of America’s awarding to the Pacific Northwest Hybrid Poplar IPM Team both its regional and its national Dow AgroScience’s Integrated Pest Management Team awards.
