Evaluation of Sulfonyl-Urea Herbicides for the Control of Itch Grass (Rottboelia cochinchinensis Clayton) on Grain Sorghum (Sorghum bicolor (L.) Moench) in Nigeria

Abstract

Aims: To address the problem of low yield due to infestation of Itch grass (Rottboelia cochinchinensis). Study Design: Randomized Block Complete Design (RCBD). Place and Duration of Study: Two trials were conducted during 2010 and 2011 raining seasons on the farm of the Institute for Agricultural Research, Ahmadu Bello University, Samaru in Northern Nigeria. Sample: Department of Agronomy, Faculty of Agriculture/Institute for Agricultural Research, Samaru Zaria, between June to December, 2010 and 2011. Methodology: The experiment consisted of nine different doses of Sulfonyl-urea herbicides and Pendimenthalin which consisted of Cinosulfuron (Setoff) and Prosulfuron (CGA 152’005) each at 0.40, 0.60, 0.80 and 1.00kg a.i/ha all compared against Pendimenthalin which is the standard herbicide known for controlling itch grass in the Nigerian savanna at 2.5kg a.i/ha and a hoe-weeded control at 3, 6 and 9 WAS as well as a weedy control. There were a total of eleven treatments in the experiment; all were laid out in a Randomized Complete Block Design (RCBD) replicated three times. The gross and net plot sizes were 24.0m2 and 22.5m2, respectively. Sorghum seeds (variety SAMSORG 14) were sown on ridges 75cm at an intra-row spacing of 25cm. Five seeds were sown per hole and later thinned to one plant per stand at 10 days after sowing (DAS). The herbicides were applied using a conventional CP 15 knapsack sprayer at a pressure of 2.1kg/cm2 and discharge rate of 240L/ha. The herbicides were applied at pre- emergence at one day after sowing (DAS) the crop. Fertilizers as 30KgN, 13KgP and 25kg K were applied same day as sorghum was sown. A second dose of 30kg N/ha was applied at 6 WAS. Weeding was done to the hoe-weeded control plot using manual hoe at 3, 6 and 9 WAS, which is the farmer’s practice in the northern Guinea savanna ecological zone of Nigeria. The crop was harvested by cutting the stem at ground level with a hand hoe and the panicles were later cut off the stems and threshed on the floor. The grains were winnowed to remove chaff and cleaned grains were then obtained. The data collected were on crop stand counted, itch grass cover score using a scale of 1 to 9, cumulative itch grass dry weight, cumulative general weed dry weight and grain yield of sorghum. Results: Among the various rates of the herbicides evaluated, application of 0.60kg a.i/ha of Cinosulfuron and 0.60 – 0.80kg a.i/ha of Prosulfuron gave better itch grass control, weed suppression, growth and yield of sorghum that were comparable to the hoe weeded control. Conclusion: It can be concluded that, the 0.60kg a.i/ha dose of both herbicides which was the most economically efficient, can be adopted as an alternative to manual hoe-weeding of itch grass in Nigeria