Phytotoxicity Evaluation of an Insecticidal Soap and Horticultural Oil on Six Turfgrass Species

Abstract

Phytotoxic effects of a insecticidal soap (Safer Insecticide Concentrate®) and petroleum-based horticultural oil (Sunspray Ultra-Fine Spray Oil®) were evaluated on four cool-season and two warm-season turfgrass species under cool and moist, and hot and dry environmental conditions. Ambient temperature, relative humidity, and water deficit level of the turfgrass had little observed effect on levels of phytotoxicity. Little or no foliar injury was observed under any environmental conditions following application of insecticidal soap or 1% and 3% horticultural oil on any turfgrass species. In most instances 5% horticultural oil initially caused slight to moderate foliar discoloration, whereas 10% horticultural oil resulted in moderate to substantial foliar discoloration depending on the turfgrass species. Zoysiagrass and creeping bentgrass were the most susceptible species to higher concentrations of horticultural oil. Phytotoxicity was relatively brief even in these more susceptible grasses, however, and there was no evidence of long-term injury to any turfgrass species resulting from any treatment under the two sets of environmental conditions investigated in this study.