The Elm Zigzag Sawfly

A new pest has emerged in the Wisconsin landscape last summer. Elm Zigzag Sawfly was confirmed in several counties across the state, according to a UW Extension report. This insect was also

 found actively feeding on a hybrid Elm variety in Kenosha County by a Wachtel Tree Science arborist during late August 2024. This article will help you be more aware of this insect, provides ways to identify insect damage on Elm trees, and some possible treatments to minimize this pest’s damage. 
 
Elm Zigzag Sawfly is native to parts of East Asia where natural predators render it a minor insect pest. It was first discovered in Europe in 2003 and has since spread from England and France to parts of Russia and Kazakhstan. The adults can fly up to 50 miles and cocoons can be found on manmade objects, allowing them to spread more easily. In 2020 the insect was found in Canada and the next year in Virginia. 2024 is the first reported presence in Wisconsin. Elm Zigzag Sawfly feeding damage is easily distinguished from other insect damage due to the distinct zigzag feeding pattern. The insect population consists of only females that reproduce asexually which can produce multiple generations per year. 

 Elm Zigzag Sawfly can cause defoliation of Elm varieties and could become a problem in your landscape. The adults can lay up to 49 eggs at a time, which hatch in 4-8 days. They feed on leaves and mature quickly over a period of 10-18 days. This speed may allow damage to “sneak up” on a homeowner if the population becomes large enough. Depending on the prior condition of an Elm, this might be a cosmetic nuisance or a potential impact on tree health. Treatment options are available. For smaller tree canopies, a sprayed contact treatment to an actively feeding population should give the most immediate results. Larger trees or trees located in difficult-to-spray locations may require soil-applied systemic products. The movement of these materials could delay the control of the population on your tree. Early detection and treatment are best to achieve desirable results. 

Wachtel Tree Science arborists are aware of this new pest. We are on the lookout for the telltale feeding damage and can help address each client’s particular tree needs as they are presented. Do not hesitate to contact our office if you suspect that this new pest may be active in your landscape. 

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