How to Eliminate Elm Leaf Beetles
As the name suggests, elm leaf beetles feed on elm tree leaves, causing the foliage to wither and making a once majestic canopy look brown or bare. Elm leaf beetles (Pyrrhalta luteola) feed on any elm species, but they prefer American elms (Ulmus americana) and Chinese elms (Ulmus parvifolia), trees that thrive in U.S. Department of Agriculture plant hardiness zones 2 through 9 and 5 through 10, respectively. Eliminate elm leaf beetles from your landscape using foliar sprays and bark banding techniques.
Examine your tree to confirm the presence of elm leaf beetles. Adult beetles have olive-green or yellow bodies and reach about 1/4 inch in length. The larvae reach about 1/2 inch long and have yellow bodies with dark stripes. Inspect the undersides of leaves as well, keeping an eye out for groups of small, yellow to gray, football-shaped eggs.
Treat all elm trees with confirmed beetle populations once the leaves reach about three-quarters of their mature lengths. By that time, the adult beetles have emerged to feed on foliage, making them more susceptible to chemicals.
Fill a hand-pump garden sprayer with a carbaryl-based insecticide mixed with water. Following the instructions and safety precautions on the product's label, add 1 to 1 1/4 tablespoons of insecticide for each gallon of water. Close your sprayer and shake it to thoroughly mix the solution.
Apply a band of insecticide at least 1 foot wide all the way around your elm tree's trunk. Spray just below the point where the lowest branches meet the trunk. The chemicals kill the larvae when they crawl down the tree to pupate near ground level.
Spray the foliage with the insecticide solution until the undersides and tops of leaves glisten with moisture. This helps eliminate egg masses and any adult beetles hiding in the canopy.
Treat the foliage again about 21 days after the first application to eliminate remaining beetles and newly hatched larvae. Reapply the bark band only if your area experiences heavy rainfall within a few weeks of the initial application.
- Hand-pump garden sprayer
- Carbaryl-based insecticide
- Avoid using insecticides unless treatment is absolutely necessary. Healthy elm trees can typically withstand minor beetle infestations without suffering any long-term damage. The University of California Statewide Integrated Pest Management Program recommends spraying your tree only when about 40 percent of the leaves have defoliated.
- Mature American elm leaves typically range from 4 to 8 inches long, while Chinese elms bear leaves just under 2 inches in length.