Several of our citizens have observed and reported what appear to be dead elm trees throughout the county in recent weeks, so I thought it a good time to explain what is happening. If you haven’t noticed these brown spots throughout wood lines before, you certainly will after reading this. The damage is widespread and the culprit is the elm leaf beetle.
The elm leaf beetle, which originated in Europe, has been active in North America for over 150 years. Adult elm leaf beetles are a dark green to yellow-green in color with a dark stripe and dark spots at the edge of each wing cover. Adults are approximately ¼ inch in length and also have three black spots behind their heads. They eat shot type holes in elm leaves, but the majority of browning we see is a result of their offspring.
Females lay between 400 and 800 yellowish orange eggs on the undersides of elm leaves that will hatch in 10-14 days. These larvae feed on the underside of leaves avoiding the large veins leaving a lacy look. After skeletonizing elm leaves for around three weeks, they move down the tree to pupate in the bark and soil at its base. By this time of year, we are probably on about the third generation of elm leaf beetles feasting on our trees.
These calls pop up in our office from time to time, but I haven’t seen a pattern of them since 2019. Annual populations of the pest are dependent on weather conditions in the winter and spring. Several naturally occurring controls can impact the elm leaf beetle. Predatory species like earwigs, stink bugs, and the ladybird beetle can all help reduce elm leaf beetle numbers, so we don’t see a lot of damage from these each year.
Of course, the question I most often get with any type of nuisance to our county’s landscape is “How do I get rid of them?” In this instance, I don’t recommend doing anything. If you are determined to protect your trees from them, There are several foliar insecticides, soil systemic insecticides, and contact insecticides that can help reduce the population of elm leaf beetles. However, when they’re on the move, they will easily spread from untreated trees back to those in your landscape.
According to UGA Forest Health Specialist, Dr. Elizabeth McCarty, “Elm leaf beetles will defoliate elm trees, causing homeowners and landowners great concern. The damage is usually not a tree mortality issue, however tree health may be compromised if trees are defoliated for numerous years in a row.”
In a worst-case scenario, the toll of these beetles can make trees more susceptible to other issues and diseases. But, that would be unusual. If your property is filled with defoliated elm trees presently, I have good news. The damage the beetles and their larvae do to elms typically has no lasting effect. Although the early leaf drop is unattractive, it rarely hinders trees from returning to their normal grandeur next season.
If you need assistance with managing an elm leaf beetle problem on your property or have more questions, you are always welcome to call our office for help at 706-743-8341 or email me at shanna.reynolds@uga.edu.