(Lepidium latifolium)
An invasive pest from East Asia first detected in Wisconsin in 2021, the elm zigzag sawfly feeds exclusively on elm trees (Ulmus spp.). Named for the distinctive zigzag feeding pattern its larvae create along leaf edges, this sawfly can cause significant defoliation when populations are high. Adults are small black wasps (5-6 mm), while the pale green larvae have characteristic dark spots along their bodies. Multiple generations per year allow populations to build rapidly during summer. The sawfly poses particular concern for American elm (Ulmus americana) and other native elm species already stressed by Dutch elm disease. Heavy infestations can weaken trees and reduce their aesthetic value, though complete tree mortality is uncommon.
Monitor elms from late spring through fall for feeding damage, especially the telltale zigzag leaf margins. Report suspected sightings to the Wisconsin Department of Agriculture, Trade and Consumer Protection.
ELM ZIGZAG SAWFLY RESOURCES
Elm Zigzag Sawfly – Wisconsin Horticulture
