Screening the Efficacy of Plant Extracted Herbicide (Pelargonic acid 71.96 %) Against Weeds in Tea Lands (Camellia sinensis L.)

Abstract

Weed is a plant, grown in an undesired place while interfereing in agricultural goals. Controlling of weeds via chemical methods is more convenient and cost effective and less disturbive to soil properties than manual weeding. Managing weeds in tea plantations has become a crucial issue due to banning of some post emergent herbicides. Thus, an environmental friendly and cost effective alternative weed management strategy is of paramount importance for the sustainable productivity of tea plantations. Therefore, this study was conducted to investigate the efficacy of 71.96% w/w EC of Pelargonic acid from Rapeseed (Brassica napus) oil to control weeds in tea lands. Six different rates of Pelargonic acid 71.96 %, (20.3, 30.4, 40.6, 50.7, 60.9 and 81.2 l/ha in 500 l/ha) were tested with three replicates at Up, Mid and Low elevations of tea lands in comparison of standard herbicide (40% MCPA) which is recommended as a selective post emergent herbicide by the Tea Research Institute of Sri Lanka. Visual observation and Quadrat samples of weeds were taken from each plot and dry weight of quadrat samples were recorded in time intervals including pre assessment. The efficacy rate of plant extracted herbicide differed based on elevation. At High elevation, 50.7 l/ha and 60.9 l/ha were the most effective rates in controlling weeds. Pelargonic acid rate 60.9 l/ha at Mid elevation and 50.7 l/ha, 60.9 l/ha and 81.2 l/ha rates at Low elevation performed well in controlling weeds in comparison to standard treatment up to 4WAA (four weeks after application). Regrowth was observed after 4WAA at High and Mid elevations and after 3WAA at Low elevation. Application of Pelargonic acid at the rate of 60.9 l/ha could be used to control weeds for a period of up to four weeks in tea lands at all elevations as cost effective range. Results of visual scoring showed that Spermacoce latifolia, Erigeron sumatrensis and Crassocephalum crepidioides-like problematic weeds at High elevation, Ageratum conyzoides and Grass weed of Cyrtococcum trigonum at Mid elevation and Spermacoce latifolia, Ipomoea obscura, Commellina diffusa and Cyperus rotundus weeds at Low elevation were most susceptible to Pelargonic acid 71.96% w/w EC. Pelargonic acid had effectively controlled some of the weeds which couldn’t control via synthetic herbicide application. The results revealed that Pelargonic acid 71.96% is a possible alternative for sustainable weed management in tea plantations as a spot application