EFFICACY OF THREE BOTANICALS AS BIO-HERBICIDE ON WEEDS ASSOCIATED WITH COWPEA AND MAIZE IN IBADAN, NIGERIA

Abstract

Cowpea [Vigna unguiculata (L.) Walp.] and maize (Zea mays L.) are main food crops widely grown in Nigeria, but their yield is reduced by weed interference. Synthetic herbicides are used to manage weeds but may be detrimental to the environment. Botanicals such as Eucalyptus torreliana (Et), Eucalyptus camaldulensis (Ec) and Leucaena leucocephala (Ll) have herbicidal properties and are eco-friendly. However, their efficacy in managing weeds on cowpea and maize fields have not been adequately documented. Therefore, efficacy of Et, Ec and Ll leaf extracts as bio-herbicide on weeds and grain yield of cowpea and maize were investigated in Ibadan, Nigeria. Leaves of Et, Ec and Ll were harvested, air-dried, milled into fine powder and assayed for phytochemicals (mg/g) following standard procedures. Milled samples (144, 108, 72, 36 and 0 g) of each botanical were dissolved in 1 L distilled water to obtain Aqueous Leaf Extracts (ALE) of 100, 75, 50, 25 and 0% (control) concentrations. Ten seeds of each of cowpea (Ife brown) and maize (DTMA-Y-STR) in petri dishes were treated with the different concentrations of ALE in a Completely Randomised Design (CRD) with triplicates. Data were collected on Seed Germination-SG (%). In pots containing 10 kg soil, cowpea and maize seeds (2 plants/pot) were each sown and arranged in a CRD. The ALE of each botanicals at 100, 75, 50, 25, 0% and paraquat (5 mL/L/ha) were applied, before and five Weeks After Sowing (WAS). Data were collected on Number of Leaves-NL of cowpea and maize at 3,5,7,9 and 11 WAS, while Grain Yield-GY (g/pot) was determined at maturity. Weed species were identified and the Relative Importance Values-RIV determined following standard procedures. Data were analysed with descriptive statistics and ANOVA at α0.05. Total phenols (32.04±0.10), tannins (27.40±0.04), saponins (20.15±0.03) were significantly higher in Ec than in Et (21.78±0.08, 17.91±0.09, 14.18±0.06) and Ll (9.47±0.08, 8.55±0.19, and 6.30±0.14), respectively. Cowpea and maize SG ranged from 80.0±0.5 (50% Ll) to 100.0±1.2 (100% Ll) and from 30.0±0.1 (control) to 100.0±0.5 (50% Et), respectively. Cowpea and maize NL ranged from 2.0±0.1 (Paraquat at 9-WAS) to 36.7±4.8 (50% Ec at 7-WAS) and from 4.4±0.2 (50% Ec at 3-WAS) to 12.9±1.5 (50% Ec at 9-WAS), respectively. Cowpea GY ranged from 0.1±0.1 (25% Ll) to 3.8±0.4 (50% Ll) and maize from 48.5±6.4 (Paraquat) to 94.3±12.0 (100% Ec). Ageratum conyzoides, Alternanthera brasilliana, Mariscus alternifolius, Mitracarpus vilosus, Oldenlandia corymbosa and Phyllantus amarus were associated with cowpea and maize. In cowpea, Mitracarpus villosus had highest RIV of 52.3 (100% Ec at 3-WAS) but reduced to 28.5 (100% Ec at 9-WAS). In maize, Mariscus alternifolius had highest RIV of 48.7 (25% Ec) and 48.0 (50% Et) both at 3-WAS and reduced to 18.9 (25% Ec) and 14.26 (50% Et) at 9-WAS. Aqueous leaf extract of Eucalyptus camaldulensis at 100% and Eucalyptus torreliana at 50% reduced Mitracarpus villosus and Mariscus alternifolius populations and enhanced grain yields of cowpea and maize. Also Leucaena leucocephala at 50% improved grain yields.