As you drive around the area, you might notice that many trees are looking like we are already in fall though summer is still here. Leaves of area elm trees have turned brown, and some may be falling off, giving them a sickly appearance. In many cases, the reason for this is, elm leaf beetles feasting on their leaves. Elm leaf beetles are a yearly concern when the second generation hatches about mid-July. This year is no exception.

Elm leaf beetles are a yearly nuisance pest that feed on elm leaves. The small green and yellow striped adults can be troublesome in homes during the fall and spring as they overwinter in houses. Adult beetles become active when the new leaves on elms emerge in the spring. They feed on the new foliage and the females lay their eggs in early May. Larva emerge and start feeding on the underside of leaves for two to three weeks, and then drop to the ground to pupate on the soil surface, or stay in the tree to pupate in the cracks of the bark. Most of the time this first generation goes unnoticed because of small numbers, and the tree producing new foliage to replace what leaves had been lost.

The second generation is where most of the damage is observed. The massive populations of beetles feeding on the leaves are what give the tree a burnt or brown appearance. This is when most people become alarmed and may notice the beetles all over their trees, or the yellow or yellow brown pupae in the cracks of the tree. Most of the time, although surprising to find, and disconcerting to see your tree looking brown early in the season, the trees is still alive and will leaf out just fine the following season.

Treatment for the beetles is usually not recommended. Most large healthy trees can withstand late season defoliation, and if anyone in the area also has beetles, then they are likely to come back to your tree. If you do want to treat, time and chemical sprays to coincide with egg hatch in either mid-May for the first generation, or early to mid-July for the second generation. Often a single application made to control the first generation is all that is required. There are several effective sprays on the market labeled for use in the control of Elm Beetles. Please make sure that you follow all directions on the container. 

Alicia Boor is the Agriculture and Natural Resources agent with K-State Research and Extension – Cottonwood District. Contact her by email at aboor@ksu.edu or call 620-793-1910.