ABSTRACT

Sweetpotato weevil (Cylas puncticollis (Boheman)) infestation results in losses of millions of dollars annually. To protect crops in modern agriculture, integrated pest management can be a good alternative to synthetic insecticides. A field study was conducted during 2018 and 2019 cropping seasons to evaluate the efficacy of some botanicals on two orange fleshed sweetpotato varieties; Umuspo/1(V1) and Umuspo/3(V2). Three experiments conducted were: (i) The use of some botanicals as aqueous extract (Tephrosia vogelii, Alchornea cordifolia and Ageratum conyzoides) (ii) Earthing-up at three levels (once, twice and thrice) and (iii) Mulching with leaves of 3 plant species; Tephrosia vogelii, Alchornea cordifolia and Ageratum conyzoides (each 50 g at five and ten weeks after planting). The experiment was laid out in Randomized Complete Block Design (RCBD) with three replicates. Plot size was 6 m². Parameters evaluated were weevil population density, progeny development, percentage colonization, root yield (marketable and unmarketable), yield-loss, damaged roots and percentage control. Results obtained from the studies indicated significant (P≤0.05) difference with aqueous botanical extracts which exhibited higher insecticidal activity against the C. puncticollis as the concentration level of the botanical extracts increased from 50 mls to 100 mls, plant extracts treatments were favourable compared to Imidacloprid and recorded significantly (P≤0.05) higher yields when compared with the control plots in 2018 and 2019. Application of 100 mls of the 3 plant extracts were effective against C. puncticollis and recorded similar yield to Imidacloprid insecticide in the two cropping seasons. The cultural practice of Earthing-up thrice and twice significantly recorded the least number of insect population density, adult insect emergence in damaged roots and had better yield and marketable roots in 2018 and 2019 compared to control plots. Mulch materials significantly (P≤0.05) reduced number of sweetpotato weevil population density, percentage colonization, damaged root, yield loss and better percentage control due to its insecticidal repelling potential on mulched plots compared to control plots. Plots mulched with T.vogelii indicated more yield in 2018 (7.15 t/ha), lower population density of C. puncticollis, least insect progeny development in 2018 (17.06) and 2019 (6.21) while A.conyzoides recorded higher yield in 2019 (5.73 t/ha). Significantly (P≤0.05) high yield of orange flesh sweetpotato was established by decomposed leaf mulch and reduced attack by C. puncticollis in both years. Umuspo/3 variety, significantly (P≤0.05) indicated higher yield and more insect progeny development than Umuspo/1variety in 2018. Umuspo/1 orange fleshed sweetpotato significantly (P≤0.05) recorded higher percentage control over Umuspo/3 variety in both years. Generally, an increase in insect population density was observed from 6weeks to 12weeks after planting, where 2019 recorded lower C. puncticollis population density over 2018 in the three experiments. Results from these studies revealed the efficacy of 100 mls botanical extract application and cultural practices of earthing-up twice, earthing-up thrice and mulching with insecticidal leaves for effective management of C. puncticollis. The botanicals used are common, abundant, eco-friendly, less hazardous, easily propagated and recommended to farmers in order to enhance orange fleshed sweetpotato production in Nigeria.