Project Overview

Reports

Commodities

• Natural Areas: forestry (hardwood)

Target Pests

• Target Pests: other

Practices

• Pest Management: chemical control

The elm zigzag sawfly (EZS) is a rapidly spreading invasive insect that threatens elm trees across the United States and Canada. Since its first North American detection in 2020, EZS has expanded to at least 14 states and four provinces. Its larvae create distinctive “zigzag” feeding damage and through rapid reproduction and multiple generations, can defoliate entire trees within a growing season. This stress weakens trees and can lead to canopy dieback.

Elms are ecologically and culturally important, particularly in urban landscapes. Disease-resistant elm varieties have become valuable replacements for species lost to other invasive pests (namely, Dutch elm disease), providing shade, cooling, wildlife habitat, and aesthetic benefits. The nursery industry also relies on elm cultivars as a major commercial product. Unchecked EZS infestations threaten these investments, and municipalities could face substantial costs from tree decline and removal.

Although pesticides can effectively manage EZS, their success depends on timing. Our preliminary research shows that systemic insecticides work best when applied weeks before EZS adults emerge. However, because this pest is new to North America, we do not know when emergence will occur. Currently, we must rely on guesswork, which could result in mistimed treatments, unnecessary pesticide use, and reduced control.

This project addresses that gap by developing a predictive model for EZS emergence in North America and translating it into a practical decision-support tool. Working with a multi-state network of collaborators in the U.S. and Canada, we will track spring emergence in 2026 using yellow sticky traps. These observations will be paired with weather and degree-day data to create a model that accurately predicts when EZS adults emerge. Once validated, the model will be incorporated into an easy-to-use online tool that provides localized predictions and recommended pesticide application windows. This tool will be accessible to arborists, municipal foresters, nursery producers, Extension personnel, and landowners.

The anticipated impact is a major improvement in integrated pest management for EZS. Stakeholders will gain a reliable method for timing treatments, reducing unnecessary pesticide use, improving control, preventing tree decline, and protecting urban and natural elm populations. By establishing this predictive framework early in the invasion, we can support more sustainable, cost-effective management across the region.