Study on the use of biopesticides against cotton insect pests under field conditions and their cost benefits.

Abstract

Cotton (Gossypium hirsutum L.) is one of the essential fibre crops. However, production is affected by several factors including low yields, high input costs, pests, and weeds infestations. Biopesticides can play a vital role in the integrated programme to address the challenges that limit production and reduce the profits for cotton farmers. This thesis consists of five chapters covering different aspects of the research on farmers' survey and biological control of cotton pests. Each chapter is presented as an independent study. The focus of this research was to (1) provide the bac-1round on cotton production in South Africa and major pests and their control; (2) survey the current status of pests on cotton and production practices; (3) evaluate the effect of different biological agents on the control of cotton pests under field conditions; (4) evaluate the efficacy of biopesticides in comparison with the insecticides against sucking pests; and (5) perform a cost analysis of cotton production using biological control agents under field conditions. This study would share an insight to build a foundation for management of major cotton insect pests. A survey was done to (1) evaluate farmers' knowledge and perceptions of cotton pests; (2) examine farmers' current practices in managing cotton pests; and (3) identify challenges and intervention opportunities to develop an efficient integrated pest management programme for cotton production. One hundred and forty farmers, mainly smallholder farmers were interviewed, and most of them planted cotton in less than five hectares of land, with 96% planting under dryland. Most farmers neither practiced conservation agriculture (95%) nor conducted soil analyses (87%) and harvested their cotton by handpicking (99%). Their knowledge of insect pests was higher than of diseases, with most of the participants not aware of nematodes (88%), or diseaseresistant cultivars (74%), while 91% were aware of insect-resistant cultivars. Most farmers relied on synthetic pesticides to control cotton pests, and only 7% used biological control. Dryland farmers reported a mean seed cotton yield of 700 kg.ha-1, and 5 000 kg.ha-1 was obtained from irrigated cotton. Most respondents were only mentored and supported by extension officers (82%). Climatic conditions (98%), labour costs (88%), and insect infestations (42%) were identified as the main constraints in cotton production. The study recommends the development of alternative control methods to minimize the use of agrochemicals.

Four biopesticides (Eco-Bb®, Bb endophyte, Bolldex®, Delfin®) were compared with a pyrethroid, Karate® against cotton insect pests, particularly the African bollworm, Helicoverpa armigera Hübner (Lepidoptera: Noctuidae). The treatments of Karate® and Bolldex® significantly reduced the H. armigera population, while the treatment of Eco- Bb® had the lowest number of damaged bolls. Plots sprayed with Karate® had significantly fewer aphids and leafhoppers. Plots treated with Bolldex® and Bb endophyte exhibited the lowest number of thrips. Plots sprayed with Karate® and Eco- Bb® had a significant effect on the whiteflies, while Delfin® had the least significant number of spider mites. The treatment of Eco-Bb® exhibited a lower cotton stainer population, while the treatment of Karate® had the lowest population of leafhoppers. The highest average seed cotton yield of 6 400 kg.ha-1 was recorded in the plots that were treated with Bolldex®. In summary, the efficacy of different biopesticides against H. armigera varied significantly; however, Karate® and Bolldex® resulted in better control of the pest. Field trials were conducted to evaluate three biopesticides, Eco-Bb®, Bb endophyte, and Eco-Noc in comparison with the insecticides Chlorpyrifos® 480 EC, Karate® EC, and Bandit® 350 SC to determine their efficacy against sucking pests, notably leafhoppers Jacobiella facialis Jacobi (Hemiptera: Cicadellidae), aphids Aphis gossypii Glover (Hemiptera, Aphididae), thrips Thrips tabaci Lind (Thysanoptera: Thripidae), whiteflies Bemisia tabaci Gennadius (Hemiptera, Aleyrodidae), red spider mite Tetranychus urticae Koch (Trombidiformes: Tetranychidae) and cotton stainers Dysdercus spp. (Hemiptera: Pyrrhocoridae). Karate® significantly reduced the leafhopper population while the biopesticides had some control of the aphids. Plots treated with Eco-Bb® and Bandit® 350 SC had the lowest number of thrips, and there were no significant differences in the populations of whiteflies. All the treatments, except for Bandit®, significantly reduced the number of spider mites. The highest average cottonseed yield of 6 395 kg.ha-1 was recorded in plots sprayed with Bandit®. Cost analysis was done by conducting two field trials (bollworm and leafhopper) to evaluate the effect of biopesticides and synthetic pesticides on controlling different cotton insect pests. The cost of biopesticides was higher than synthetic pesticides. Delfin® was the most expensive treatment at R 7 980/ha, while Chlorpyrifos® 480 EC had the lowest price of R 370/ha.

The highest input cost of R 7 200/ha was recorded from labour costs incurred during weed control. The highest total costs of R 21 502/ha were incurred where Eco-Bb®, Bb endophyte and Eco-Noc were applied. In the bollworm experiment, the lowest production costs per hectare were observed from the treatment with Karate® EC (R 19 282). The maximum seed cotton yield of 6 818 kg.ha-1 was recorded in Bolldex® treated plots while Karate® EC treated plots had the highest net profit of up to R 19 148 per hectare and mean benefit-cost ratio of 1.8. In the leafhopper trial, the highest seed cotton yield was obtained from the Bandit® 350 SC treated plots (6 394 kg.ha-1). Plots, where Bandit® 350 SC was applied, had the maximum net profit of R 22 686 with a benefit-cost ratio of 2.