Efficacy Evaluation of Different Herbicides to Control Echinochloa crus-galli and Paspalum distichum in Transplanted Rice

IntroductionContinuous rice cultivation in the paddy fields of northern regions in Iran has led to the spread of weeds such as Echinochloa crus-galli and Paspalum distichum gradually. The presence of these grass weeds in paddy fields leads to waste of water and nutrients and adversely affects on rice productivity. Herbicide application helps for keeping the fields free of weeds during the critical period and minimize the costs of weeding and allows for selective weed control. No repeated application of herbicides or mixed application of herbicides are necessary, because these strategies need to prevent herbicide resistance in weeds. This experiment aimed to assess and compare the effectiveness of some herbicides, including metsulfuron-methyl, tiobencarb, bispyribac sodium, triafamon + ethoxysulfuron, cyhalofop-butyl, and the tank mixed application of cyhalofop-butyl and bispyribac sodium, in controlling grassy weeds in the rice fields.  Material and MethodsA field experiment was conducted in Gilan Agricultural and Natural Resources Research and Education Center (Rasht) in 2021, utilizing a Randomized Complete Block Design (RCBD) with three replications and 15 treatments, including tiobencarb 50%EC at 2750 and 3000 g­ a.i. ha-1, bispyribac sodium 40%SC at 26 g a.i. ha-1, triafamon+ethoxysulfuron 30%WG at 37.5 and 45 g a.i. ha-1, cyhalofop-butyl 20%OD at 100 g a.i. ha-1, bispyribac sodium 40%SC at 26 g a.i. ha-1 + cyhalofop-butyl 20%OD at 100 g a.i. ha-1, metsulfuron-methyl 60%DF at 6 and 8 g a.i. ha-1, pertilachlor 50%EC at 875 g a.i. ha-1, twice hand weeding, and weedy check. Thiobencarb, pertilachlor, and triafamon + ethoxysulfuron were applied in water, five days after transplanting, and cyhalofop-butyl, metsulfuron-methyl, and bispyribac sodium were applied to the weeds at the two- to four-leaves stage, using a knapsack sprayer equipped with a flat fan nozzle. Weed control via application of herbicides was evaluated visually based on the European Weed Research Society rating scale and weed density and biomass were assessed. The yield of rice from each plot was measured. The data collected for different parameters were subjected to analysis of variance (ANOVA) using R-studio and the treatment means were compared using Duncan's Multiple Range Test at a significance level of 1%.Results and DiscussionAll weed control treatments significantly increased the weed control efficiency (WCE) over the weedy check. Triafamon + ethoxysulfuron and tiobencarb in both examined doses had the highest WCE in reducing E. crus-galli pressure with 100% control. After that the effectiveness of pertilachlor at 875 g a.i. ha-1and cyhalofop-butyl at 100 g a.i. ha-1 in reducing E. crus-galli density was ≥90% and biomass reduction was ≥78%. There were no significant differences between these treatments in controlling E. crus-galli. The highest WCE in P. distichum control was observed in applying triafamon + ethoxysulfuron at doses of 37.5 and 45 g a.i. ha-1 with ≥91.1% and ≥94.4% density reduction and ≥95.6% and ≥99.8% biomass reduction, respectively; followed by application of cyhalofop-butyl with ≥83.6% and ≥79.7%, density and biomass reduction, respectively. After that, tiobencarb in both doses resulted in ≥72% density reduction and ≥84.5% biomass reduction. There was no significant difference between these treatments in P. distichum control. Pertilachlor was not very effective in controlling of P. distichum; its efficacy was 48.8, 56.5, and 78.4% biomass reduction, in three samplings, respectively. The highest efficacy of metsulfuron-methyl in controlling E. crus-galli and P. distichum was 75.9 and 73.1%, respectively for biomass reduction in the first sampling in the application of 8 g a.i. ha-1. Herbicide application resulted in improved rice grain yield compared to the weedy check. The highest grain yield of rice was achieved with tiobencarb at doses of 3000 and 2750 g a.i. ha-1, yielding 5051 and 4965 Kg ha-1, respectively. There was no significant difference between observed manually weeded treatment and thiobencarb treatments, and also with bispyribac sodium, pertilachlor, triafamon + ethoxysulfuron in both doses (45 and 37.5 g a.i. ha-1), and cyhalofop-butyl; these treatments increased grain yield by 68.4, 65.5, 54.56, 52.8, 39.2, 35.4, 34.6%, respectively, compared to the weedy check. ConclusionsThe results of this research showed that application of triafamon + ethoxysulfuron at 37.5 g a.i. ha-1 or thiobencarb at 2750 g a.i. ha-1 applied at 3-5 days after rice seedlings transplanting into the water, or application of cyhalofop-butyl at 100 g a.i. ha-1 in the form of a foliar spray in the stage of two- to four-leaf of grass weeds were the efficient control practice for both grass weeds (E. crus-galli and P. distichum) in paddy field.