Growth and management of Isachne miliacea Roth. in transplanted rice

Isachne miliacea Roth. (Isachne) commonly known as blood grass is one of the troublesome graminaceous weed in wetland rice ecosystems of Kerala. The stoloniferous growth habit, with roots forming at each node, makes hand weeding difficult. Ploughing infested fields further promotes vegetative spread, as the rooted fragments quickly re-establish. The grass also gets propagated through seeds. Experiments were conducted during 2021–2024 at four locations in the farmers’ fields infested with Isachne to develop effective management strategies in transplanted rice. Seven treatments were evaluated in a randomized complete block design with three replications. The treatments included: pre-plant application (PPA) of glyphosate 820 g/ha, post emergence application (PoE) of penoxsulam + butachlor (ready-mix) 820 g/ha, penoxsulam + cyhalofop-butyl (ready-mix) 150g/ha, fenoxaprop-p-ethyl 60 g/ha, fenoxaprop-p-ethyl 120 g/ha, hand weeding twice at 20 and 40 days of transplanting rice (DAT) and un-weeded check. Herbicides were sprayed at 25DAT so as to ensure establishment of Isachne spp. to enable foliar absorption of herbicides. Cyhalofop-butyl and bispyribac-sodium were found ineffective against Isachne in a pilot study. The absolute growth rate of Isachne exceeded 2.5 g/m2/day during the initial 40 days of weed growth. Fenoxaprop-p-ethyl at 120 g/ha sprayed at 25–30 DAT, registered higher weed control efficiency (WCE) and rice grain yield and was comparable to hand weeding. Glyphosate (PPA) 0.82 kg/ha, 2–3 weeks before ploughing was another effective option with WCE of 88 % and was comparable with fenoxaprop-p-ethyl 120 g/ha (WCE of 85%). Penoxsulam + butachlor (pre-mix) and penoxsulam + cyhalofop-butyl (ready-mix) were ineffective with more than 50% reduction in rice grain yield and in un-weeded check yield reduction was 74%. Application window of fenoxaprop-p-ethyl 120 g/ha should be 25–30 DAT so as to avoid risk of crop phytotoxicity and to ensure effective coverage and herbicide absorption by the weed. Garrett ranking analysis indicated that previous-season fallowing and ploughing of already infested fields were the most important factors contributing to Isachne miliacea infestation in succeeding rice crop.