Evaluation of herbicides and manual weed control methods in the establishment of Theobroma cacao L. in Cross River State of Nigeria

Field trial was conducted at the Cocoa Research Institute of Nigeria (CRIN), Ajassor substation, Cross River State, Nigeria between 2015 and 2017 to evaluate the effect of different weed control methods on the growth and yield of cocoa during their early years of establishment. Glyphosate and paraquat were applied at 480, 720, 960 and 1440 gram of active ingredient per hectare using very low volume (g a.i. ha-1 vlv) while manual weeding (i.e. slashing with cutlass) was used as the control. A Nigeria commercial cocoa variety Tc series, also known as 18-month cocoa, was established at a CRIN recommended spacing of 3 x 3 m, laid out in a Complete Randomized Block Design with four replications. All young cocoa stands were ring weeded at 50 cm diameter and covered with black polythene bags before the spraying of herbicides during the first six months of establishment to reduce injury that could result from the drifting of herbicide solution to plants during their early growth stage. Data was collected on the plant height, stem girth and number of leaves of cocoa plants while the cocoa dry beans weight and labour cost for each treatment were determined. The results showed that 960 g a.i. ha-1 vlv was the best herbicide application rate while plots under glyphosate at 960 g a.i. ha-1 vlv produced significantly higher values of plant height, stem girth and number of leaves at (p=0.05) than both paraquat at 960 g a.i. ha-1 vlv and manual weeding. Labour cost for controlling weeds with either glyphosate or paraquat at all application rates were considerably lower than cost for control (manual weeding). Glyphosate at 960 g a.i. ha-1 vlv is recommended for weed control in cocoa plantation because it encouraged higher growth and yield performance of cocoa than other treatments, had considerably cheaper cost of application than paraquat at 960 g a.i. ha-1 vlv and manual weeding, and it also ensured a weed-free environment over a longer period of time than the other treatments.