Herbicides for Monochoria (Monochoria vaginalis) Control in Transplanted Rice

Monochoria is an introduced weed to Iran. Two field experiments were conducted to identify soil-applied and foliar-applied herbicides for monochoria control in transplanted rice. Pre-packaged herbicides triafamone plus ethoxysulfuron applied at 40 g ai ha-1, pyrazosulfuron-ethyl plus pretilachlor at 382.5 g ai ha-1, and pendimethalin plus clomazone at 1200 g ai ha-1 reduced monochoria biomass by 100%, 100%, and 14%, respectively, and a single application of flucetosulfuron at 30 g ai ha-1, pendimethalin at 990 g ai ha-1, thiobencarb at 2750 g ai ha-1, and pretilachlor at 1000 g ai ha-1 by 100%, 99%, 75%, and 56%, respectively, compared with the nontreated control. Tank-mixed bensulfuron-methyl at 45 g ai ha-1 with pretilachlor, thiobencarb, or pendimethalin provided 100% control of monochoria. Rice height, and straw and grain yield were greater in herbicide treatments than in the nontreated and hand-weeded control, indicating the advantages of chemical monochoria control over manual weeding. Full-season monochoria interference reduced rice grain yield by 32%. In the second study, foliar-applied herbicides triafamone plus ethoxysulfuron, flucetosulfuron, 2,4-D at 1080 g ai ha-1, dicamba plus 2,4-D at 928 g ai ha-1, bispyribac-sodium at 31.25 g ai ha-1, bentazon plus MCPA at 1150 g ai ha-1, pyribenzoxim at 30 g ai ha-1, and propanil at 5400 g ai ha-1 applied at 4-5 leaf seedlings of monochoria provided ≥97% control and prevented 100% of its regrowth, with the exception of propanil. This study shows that monochoria control can be achieved by many residual and foliar-applied herbicides with different mechanisms of action.