Title: Investigation on the efficacy of some herbicides on chemical control of Monochoria (Monochoria vaginalis)
Author: Bijan Yaghoubi
Abstract: Monochoria vaginalis is one of the most invasive broadleaf monocot weeds of paddy fields, which three decades after the first report of its presence in Iran, now has infected about 62000 ha of Guilan and Mazandaran provinces paddy fields. Some characteristics of monochoria, such as late emergence, resistance to flooding, regrowth after hand weeding, completing the life cycle after rice harvest and lack of sufficient information on chemical control, have led to the fast spread of monochoria. Five experiments in order to investigate the efficacy of herbicides in monochoria controlling and also studying the rice yield loss in interference with monochoria at different levels (0, 50, 100 and 150% of the recommended rate) of N.P.K fertilizers, in pot and field conditions from 2018 to 2020 at the Rice Research Institute of Iran was conducted. The results of the first experiment showed that the efficacy of herbicides in the post-emergence application (about 3 leaf seedlings of monochoria) and in potting conditions was very different. Common herbicides thiobencarb (EC 50%), pendimethalin (EC 33%), oxadiargyl (EC 3%) and benesulfuron methyl (DF 60%) provided 24, 41, 46 and 77% efficacy, respectively, and the new herbicides triafamone + ethoxysulfuron (council WG 30%) , pyrazosulfuron + portilachlor (pirazchlor, TB 17%) and flucetosulfuron (WG 10%) efficacy was 93, 99 and 100% in monochoria biomass reduction respectively. According to the results of the second experiment, application of the herbicides pendimethalin, flucetosulfuron, pretilachlor (EC 50%), council, pendimethalin + benesulfurono methyl, pretilachlor + benesulfuron methyl, two formulation of pyrazosulforoun (WG 75% and WG 10%) + pretilachlor, pendimethalin + clomazone (EC 33% + DF 60%) and thiobencarb in pot condition in the open air as preemergence herbicides provided ≥ 90% reduction in monochoria biomass compared to control treatment. Preemergence application of soil-applied herbicides in field conditions for two years indicated good performance (≥90%) of the herbicides pendimethalin, flucetosulfuron, council, pendimethalin + benesulfuron methyl, pretilachlor + benesulfuron methyl, pirazchlor and pyrazosulforoun + pretilachor (eros gold DF 30.75%) and reduction of thiobencarb efficacy in field (80%) compared with pot and lesser efficacy of bispyribac sodium, pretilachlor and pendimethalin + clomazone (≤63%). According to the results of the fourth experiment, foliar-applied herbicides 2,4-D (SL 72%), dicamba + 2,4-D (SL 46.4%), bispiribac sodium (SC 40%), bispiribac odium (SC 12.5%), council and piribenzoxime (EC 36%) provided ≥92% efficacy in field and old common herbicides propanil (EC 36%) and MCPA + betazone (bazagran SL 46%) efficacy was less than 60% in monochoria control. With the manual removal of all weeds and the whole season competition of the monochoria with rice, the average reduction of paddy grain yield in weedy control compared to hand weeded control during two years of field study was 35%. Rice yield in herbicide treatments of council, pirazchlor, erosgold, flucetosulfuron, pretilachlor + besnsolforoun and pendimethalin + bensulfuron in the first year of the experiment was higher than that of hand weeding control and in the second year, there was no statistical difference between chemical control with the hand weeded control. Monochoria biomass was affected by fertilizer and interference with rice. Monochoria biomass in monoculture at the recommended amount of fertilizers was about 230 g/m2 and increased significantly with increasing the fertilizer. Rice interference reduced the biomass of Monochoria by about 50%. The grain yield of rice in pure cultivation in all fertilizer treatments was significantly higher than its value in competition with monochoria. The maximum yield of rice in hand weeded treatment and in interference with monochoria was 4328 and 3212 kg/ha, respectively, which represents 26% of yield loss. In general, increasing the fertilizer to the recommended values was associated with an increase in yield, but consuming more than it led to a decrease in rice yield.
Keywords: Invasive weed, Aquatic ecosystems, Overwintering, Nutrition management