Preliminary observations on use of Beauveria bassiana for the control of the sweet potato weevil (Cylas sp.) in South Africa

Abstract

Abstract Sweet potato weevils (Cylas puncticollis and C. formicarius) are notorious pests of sweet potato and cause severe losses in marketable yield. The study tested the use of Beauveria bassiana ((Balsamo) Vuillemin) (Deuteromycota: Hyphomycetes) for controlling sweet potato weevils. An experiment was conducted using four treatments: 1) dipping sweet potato cuttings in solution of 1 g/litre B. bassiana before planting, 2) spraying with the registered chemical Deltametrin at 50ml/100litre every 2 weeks for four months after planting, 3) spraying the leaves every 2 weeks with B. bassiana (10 g/100 litre) for four months after planting; and 4) a control (sprayed with distilled water). The experimental design was a Latin square with split plot design: pest management strategy as main plot factor and cultivars (Bophelo, Ndou and Blesbok) as subplot factors. Spraying with B. bassiana significantly reduced the percentage of insect damaged roots (5.31%) compared to the control (13.75%). Dipping did not significantly reduce the number of insect damaged roots (12.13%). There was no significant difference between the chemical spray (5.88% insect damage) and spraying with B. bassiana (5.31% insect damage). The preliminary investigation indicated that B. bassiana can be considered as an alternative control method for the sweet potato weevil.