Effects of Simulated Acid Rain on Efficacy of Methoxychlor for ELM Leaf Beetle Control, Delaware County, Ohio, 1987

Abstract

Abstract Three-year-old potted trees of a single clone, Ulmus (hybrid '970'), growing under lathhouse conditions were sprayed with methoxychlor and subjected to simulated acid rain (SAR) treatments to determine whether insecticidal efficacy against elm leaf beetle (ELB) adults was affected. The experimental factors were as follows: methoxychlor applied at 0.5%, 3 SAR treatments (pH 3.0; pH 4.2; none), and 3 replicates each. Three elm trees not treated with methoxychlor or SAR served as controls. SAR solutions were made by adjusting the pH of deionized water with 2 parts H2S04 and 1 part HN03 and were applied through beta-fog nozzles at 90 kPa in chambers equipped with platforms 1.2 m diameter, revolving at 2.4 revolutions/min. SAR treatments began twice weekly on 4 Sep and continued for 12 wk. Each SAR event delivered 1.27 cm (0.5 inches) in 35 min (30.5 cm; 12 inches total). Trees were sprayed with methoxychlor to runoff on 3 Sept (20°C, 40% RH, winds 5 mph) using a compressed-CO2 R&D Model TS backpack sprayer equipped with a no. 5500 adjustable cone-tip nozzle opened one-half turn from full-closed at 206.8 kPa pressure. At 0, 7, 21, 42, and 84 days after treatment (DAT), 5 leaves were harvested from each tree for use in ELB bioassays. Each leaf was placed in a plastic Petri dish (15 mm) at 25°C on a 15:9 (L:D) schedule with 3 pair ELB reared on U. putnila and maintained as adults on an artificial diet. At each bioassay, ELB mortality was determined after 24 h. Insecticide phytotoxicity was determined at 1 and 84 DAT.