Management of Salvinia (Salvinia molesta D.S.Mitch.) in Wetland Rice Ecosystem

Abstract

Giant salvinia (Salvinia molesta) is a problematic aquatic fern found in wetlands. Recently, severe infestation of the weed has been observed in the low-lying rice fields in India. An experiment was conducted at Kerala Agricultural University to investigate the effectiveness of different rice herbicides and soil amendments for managing salvinia. The trials were conducted in tanks, and a few effective herbicides were subsequently tested in the field. Changes in major water quality parameters were also monitored. The tank study comprised 15 treatments; lime and gypsum (each at 0.1 kg/m²), acetic acid, salicylic acid, NaCl, and CuSO₄, (each at 5% strength), and rice herbicides such as carfentrazone-ethyl (0.02 and 0.04 kg/ha), 2,4-D amine (1 kg/ha), cyhalofop-butyl + penoxsulam (0.15 kg/ha), florpyrauxifen-benzyl + cyhalofop-butyl (0.15 kg/ha), butachlor + penoxsulam (0.82 kg/ha), glufosinate-ammonium (0.3 and 0.5 kg/ha) along with an untreated check. In tank study, glufosinate-ammonium, carfentrazone-ethyl, cyhalofop-butyl + penoxsulam, florpyrauxifen-benzyl + cyhalofop-butyl, butachlor + penoxsulam, acetic acid, salicylic acid, and CuSO₄ gave more than 80% salvinia control. However, regrowth was observed in acetic acid, salicylic acid, and CuSO₄. Under field conditions, the weed control efficiency of all the treatments were more than 80%. Salvinia competition resulted in 55% reduction in rice grain yield. Though noticeable changes in water pH and EC were observed after applying lime, gypsum, and CuSO₄, these alterations did not suppress the salvinia growth. Effective management of salvinia infestation in wetland rice can be achieved through post-emergent spray of premix herbicides; florpyrauxifen-benzyl + cyhalofop-butyl, cyhalofop-butyl + penoxsulam, pretilachlor + pyrazosulfuron ethyl, butachlor + penoxsulam, or carfentrazone-ethyl or florpyrauxifen-benzyl, along with a wetting agent. For pre-plant control glufosinate-ammonium is a suitable herbicide.