Abstract Infested plants growing on campus at The Ohio State University, Ohio Agricultural Research and Development Center, near Wooster were chosen for evaluating efficacy of insecticides against first and second generation fall webworm caterpillars. A KWH backpack mistblower operating at 0.5 throttle and aperature setting 3 was used to apply finished spray to the web and surrounding foliage on 3 (Jul treatment) or 4, single-tree replicates per treatment. Application on 3 Jul occurred under sunny skies at 27°C with a breeze of 15-25 kph when first generation larvae were ca. 7-10 mm long. Application on 22 Aug occurred when the sky was cloudy at 21°C with only a slight breeze when the larvae were ca. 25-30 mm long. Application on 24 Aug occurred under sunny skies at 18°C with no breeze.Treatment effectiveness was evaluated 5 to 7days after application by dismantling the web in each sprayed tree and counting living and dead larvae.