Integrated Management of Sweet Potato Weevil (Cylas spp.) Based on Planting Material Treatment and Spray Regime in Northern Ghana

Abstract

Aims: The sweet potato weevil (Cylas spp.) exerts the most biotic threat in sweet potato production in most countries. A dual challenge exists regarding integrated management of the Cylas spp. in Ghana, namely, the wide use of farmer-saved planting material with higher infestation and the cryptic feeding habit. Study Design: The experimental set-up was a split plot with the main plot as planting material treatment and sub-plot as spray regime. Place and Duration of Study: The study was conducted at Voggu in the Kumbungu District, and Gani in the Kassena-Nankana East Municipal of Ghana from July to October in 2022 and 2023. Methodology: The planting material treatment comprised an untreated control, shea (i.e., vine cuttings dipped in shea butter slurry), wood ash (i.e., vine cuttings dipped in wood ash solution), neem powder (i.e., vine cuttings dipped in aqueous neem seed powder at 75 g/l), insecticide + fungicide [i.e., vine cuttings dipped in cocktail of K-Optimal (Lambda-Cyhalothrin 15 g/l + acetamiprid 20g/l EC) at rate of 0.4ml/L + fungicide (Mancozeb 800 WP) mixture for 60 sec.], and Furadan (Carbo-furan placed in furrows at planting). Results: The results are discussed in relation to plant establishment, leaf damage, stover yield, storage root yield, stem/root damage and yield losses. Leaf damage showed a sigmoid peak at 6 WAP probably, indicating the critical window to administer control measures to achieve matching results. Significant increase (p<0.01) in root yield occurred in insecticide (19.1t/ha) and neem seed extract (1.8t/ha) sprays compared to the control (11.0 t/ha). Yield losses hovered at 4.6% with insecticide spray, 6.2% with neem seed extract and 10.5% with control.  Integration of planting material treatment with insecticide spray showed benefit cost ratios ranging from 2.5 to 40.2. A dual management strategy involving planting material treatment and preferably, insecticide spraying at 6 WAP could reduce infestation build-up.