Sequential use of pre-and post-emergence herbicides for weed management in castor (Ricinus communis)

Abstract

Castor oil is an industrially significant product that serves as a chemical platform for the production of numerous products and their derivatives, including sebacic acid. Although the output of castor (Ricinus communis L.) is still significantly hampered by weed competition, resulting in 28–30% yield losses. This study sought to assess the effectiveness of herbicides on rainfed castor throughout the rainy (kharif) seasons of 2022–23 and 2023–24. The experiment comprised 12 treatments, one weed-free check; one weedy check; one mechanical weed management; and nine herbicide treatments [includes three pre-emergence (PE) applications (diclosulam, metribuzin, and pendimethalin), one early post-emergence (EPOE) (imazethapyr), and one post emergence herbicide (POE) (quizalofop ethyl)]. The PE spray of diclosulam 84% wdg at 20 g/ha on 3 days after sowing (DAS), trailed by an EPOE of imazethapyr 10% sl at 100 g/ha on 15 DAS, and supplemented with power weeding on 30 DAS, generated the least number of weeds of 3.24, 3.84, and 4.06 weeds/m² at 25, 50, and 75 DAS, respectively (as per two-year pooled data). The total dry weight of weed was recorded as 2.24, 2.87, and 3.51 g/m² at 25, 50, and 75 DAS, in that order. The highest weed control index (WCI) was reported by this combination of 83.8, 83.9 and 84.8% on 25, 50, and 75 DAS, respectively, with corresponding weed control efficiency (WCE) values of 76.7, 76.5 and 83.2%, respectively. With a castor yield of 1,735 kg/ha, a net revenue of ₹75,540/ha, and a benefit cost ratio (BCR) of 2.64, this treatment produced the lowest weed index (4.9%), the highest herbicide efficiency index (6.93%), and the lowest weed persistence index (0.46). Following this, diclosulam 84% wdg was applied PE on 3^rd DAS @20 g/ha. On 15 DAS, imazethapyr 10% sl was applied as an EPOE herbicide @100 g/ha, and on 30 DAS, quizalofop ethyl 5% ec was applied POE @50 g/ha. The number of spikes/plant (13.9), effective spike length (57.7 cm), yield of castor (1,779 kg/ha), net revenue (₹77,760/ ha), and BCR (2.69) were all higher after power weeding at 20, 40, and 60 DAS.