Efficacy of three biopesticides against cotton pests under field conditions in South Africa.

Cotton is a major fibre crop grown in South Africa; and is subjected to pest attacks, which reduce its yield and profitability for farmers. Field trials were conducted in 2017 and 2018 to evaluate three biopesticides, namely, Eco-Bb®, Bb endophyte, and Metarhizium rileyi in comparison with the insecticides Chlorpyrifos® 480 EC, Karate® EC, and Bandit® 350 SC. The objective was to determine their efficacy against sucking pests, leafhoppers Jacobiella facialis , aphids Aphis gossypii , thrips Thrips tabaci , whiteflies Bemisia tabaci , red spider mite Tetranychus urticae, and cotton stainers Dysdercus spp. Karate® significantly reduced the leafhopper population and outperformed all the other treatments. Eco-Bb® and Bb endophyte did not control the aphids in 2017. However, in 2018 the best aphid control resulted from the biopesticides used. In 2017 plots treated with Eco-Bb® had the lowest number of thrips, while in 2018 plots treated with Bandit® had the least thrips, followed by treatments with M. rileyi and Karate®. There were no significant differences in the populations of whiteflies, however, insecticides were more effective than the biopesticides. All the treatments, except for Bandit®, significantly reduced the number of spider mites compared in 2017. Applications of Eco-Bb® and Bb endophyte significantly reduced spider mites in 2017, while in 2018 plots treated with Karate®, followed by M. rileyi , resulted in the lowest number of spider mites. Application of Bb endophyte, Chlorpyrifos®, and Karate® resulted in the lowest number of cotton stainers. The highest mean cottonseed yields of 6395 kg ha⁻¹, 6295 kg ha^−1, and 6141 kg ha⁻¹ were recorded in plots sprayed with Bandit®, Bb endophyte, and Eco-Bb®, respectively. Biopesticides and chemical insecticides can be combined or alternated for future IPM programmes to control cotton pests. • Karate® significantly reduced leafhoppers while Eco-Bb®, Bb endophyte, and Metarhizium rileyi reduced aphids. • Eco-Bb® and Bandit® reduced the thrips population. • All the treatments, except for Bandit®, significantly reduced the spider mite populations. • Bb endophyte, Chlorpyrifos®, and Karate® reduced the number of cotton stainers. • Plots treated with Bandit® had the highest cottonseed yields of 6395 kg ha⁻¹ [ABSTRACT FROM AUTHOR]