Abstract
A two year (2015 and 2016) experiment was conducted to evaluate the phytotoxicity of selected herbicides on some cultivars of cassava (Manihot esculenta Crantz) in a screen house at the University of Uyo Teaching and Research Farm, Uyo. A split-split plot arrangement in a randomized complete block design, replicated three times was used. Main treatments were three cassava cultivars; (TMS 97/0162, TMS 01/1412 and local cultivar- Obubit okpo), sub treatments were four types of herbicides; Atrazine, Diuron, Raft and Primextra. The sub-sub treatments were five rates of herbicide application; 0, 1.0, 2.0, 3.0 and 4.0 kg a.i/ha. Data collected on stand establishment, cassava height and phytotoxicity were subjected to analysis of variance. Results showed that the stand establishment did not differ significantly among the cassava cultivars. Stand establishment and plant height (cm) differed significantly across herbicides and rates of application in 2015 and 2016 respectively. High stand establishment was recorded in plots treated with Raft followed by Diuron compared to the mortality rate in Atrazine and Primextra treated plots. Plant height decreased as the rate of application of herbicides increased above 2.0kg a.i/ha across all herbicides. Phytotoxicity of herbicides on cassava stand was also significantly (p< 0.05) affected in both cropping seasons. Significant differences were observed in the injury (mortality) rate of the cassava stands. Primextra was more lethal, followed by Atrazine compared to other herbicides irrespective of the cultivar. Primextra applied at the rate of 4.0 kg a.i/ha showed the highest phytotoxicity across the selected cassava cultivars. Raft applied at the rate of 2.0 kg a.i/ha had less phytotoxicity on cassava cultivars. Based on the findings, Raft application at the rate of 2.0 kg a.i/ha is recommended for cassava production in the ecology.