Control of Elm Leaf Beetle with Trunk Injected Insecticides, 1993-1994

Plots were established using a series of street trees, approximately 60-ft (24 inch DBH), which lined a municipal park in Denver, CO. Two different injection techniques were employed in the trial. Arbor, capsules (Tree Technologies, Inc.) were applied 30 Jun by drilling a series of holes in the root flare of the tree. Rate of application was one capsule per 6 inch of circumference at breast height. Individual capsules contained either 5 ml of Bay NTN 33893 200SL (imidacloprid) or 4 ml of Avid (abamectin), which were allowed to drain completely. Direct trunk injections were made 26 Jul using a modified syringe that placed 1 ml of insecticide under the bark of the trunk. Injection sites were similarly made at intervals of 6 inches of tree circumference at breast height. Plot design was a RCB with 4 replications. No sampling was conducted during 1993, since treatments were applied after considerable defoliation had occurred. Plots were sampled twice during the 1994 season following the first and second generations of the elm leaf beetle. Leaves from 4 branches per tree were evaluated for amount of defoliation (skeletonizing). The rating system was: 0 = No damage present, 1 = 1-10% skeletonizing per branch, 2 = 11-20% skeletonizing per branch, 3 = 21-30% skeletonizing per branch, 4 = 31-40% skeletonizing per branch, 5 = 41-50% skeletonizing per branch, 6 = 51-60% skeletonizing per branch, 7 = 61-70% skeletonizing per branch, 8 = 71-80% skeletonizing per branch, 9 = 81-90% skeletonizing per branch, 10 = 91-100% skeletonizing per branch.