Control of European Elm Scale with Trunk Injected Insecticides, 1993-1994

A shelterbelt planting of mature Siberian elm trees located at the Colorado State Forest Service Nursery (Ft. Collins, CO) were used to test the efficacy of selected systemic insecticides applied with two different trunk injection systems. Arborx capsules (Tree Technologies, Inc.) were applied 30 Jun by drilling holes in the root flares of the tree. Rate of application was one capsule per 6 inch of circumference at breast height (cbh). Individual capsules contained either 5 ml of Bay NTN 33893 200SL (imidacloprid) or 4 ml of Avid (abamectin), which were allowed to drain completely into the tree. 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 cbh. Plot design was a RCB with 5 replications. Evaluations in the first year of the trial (10 Aug 1993) were made by assessing percent mortality of instar II nymphs on 10 leaves per tree. Evaluations the following spring (15 Jun 1994) were based on counting the number of overwintered scales on two 18 inch twig samples per tree.