The USDA Forest Service’s Eastern Region Forest Health staff released a pest alert on elm zigzag sawfly, an invasive insect that defoliates elm trees.
The elm zigzag sawfly has the potential to spread quickly. Since its first North American detection in 2020 in Quebec, it has been found in numerous states in the Northeast, mid-Atlantic, South and Midwest. The elm zigzag sawfly is a strong flyer with the ability to disperse up to 55 miles a year. People may inadvertently bring it to new locations when they move trees, leaf litter or even inanimate objects that have its cocoons attached.
The adult is a shiny black insect — about 8 millimeters long — with dark wings. The yellowish-green larvae are about 11 millimeters long with distinctive markings. Another telltale sign of an infestation is the zigzag pattern the larvae create when they feed on elm leaves.
Elm zigzag sawfly infestations can lead to severe or almost total defoliation of elm trees. Currently, none of the pesticides available for general sawfly management are specifically labeled to control this insect.
See the USDA’s pest alert for more information on where the insect is found, how to identify it, the fly’s appearance at different stages, the damage it can cause and how big of a threat it is to elm trees.
