“Help! My Elm Trees are being eaten!” has been a common statement in the Extension office lately. I’ve had at least two clients with the same issue, and my suspicion is that the true number affected is much higher. The culprit is the larvae of the elm leaf beetle, or Xanthogalerucia luteola.
The elm leaf beetle originated in Europe but has been well established in North America for over 150 years. It is known for feeding on all species of elms, from Siberian and English types to American, rock, slippery, and other varieties. The beetle is a significant pest for shade and ornamental elms but typically less of an issue in the forest. They can seek to overwinter in one’s home, but while their presence may be alarming, they will not feed on or damage anything within the home.
Elm leaf beetles overwinter as adult beetles in protected sites. In April and May, overwintered adult beetles emerge and move to elm trees to feed and reproduce. Adult elm leaf beetles are a dark green color during the overwintering phase, and lighten to yellow-green 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. After a few weeks of feeding, female beetles will lay between 400 and 800 yellowish orange eggs on the undersides of elm leaves. The larvae hatch in 10-14 days and will feed for three weeks or so before moving down the tree to pupate in the bark and soil at the base of the tree. The larvae start out dark and hairy, but mature to be dull yellow, with two dark stripes along their sides and dark heads and legs. The 10-15 day pupation period results in a surge of adult beetles, who can produce a second and sometimes third generation, depending on the weather.
The majority of the damage from elm beetles come from the larvae stage, where they feed on the underside of elm leaves, a process called skeletonizing. The damaged leaves then turn brown, making them appear scorched. Adult leaf feeding shows up as “shot hole” patterning in the leaves as they eat through the entirety of the leaf surface. At best, the damage to elm leaves can be unattractive and result in early leaf drop, but at worst, the damage can reduce tree growth and make them more susceptible to other issues and diseases.
Annual populations of this pest are often dependent on weather conditions in the winter and spring but there are a fair number of naturally occurring controls that can impact the elm leaf beetle. Predatory species like earwigs, stink bugs, and the ladybird beetle can all help reduce elm leaf beetle numbers. There are several foliar insecticides, soil systemic insecticides, and contact insecticides that can help reduce the population of elm leaf beetles. It’s important to note that the insect does travel well, and migration and infestation of your trees from untreated trees is a real concern. If you need assistance with managing an elm leaf beetle problem on your property, let us know at uge3181@uga.edu or 706-359-3233.
