Management of Pistia stratiotes L. in the rice ecosystem

Abstract

Pistia stratiotes L. (commonly known as water lettuce), a free-floating, stoloniferous aquatic macrophyte belonging to the family Araceae, has recently emerged as one of the world’s most problematic aquatic weeds. A pot culture experiment evaluated the efficacy of various herbicidal and eco-friendly chemicals against Pistia in completely randomised design (CRD) with 11 treatments replicated thrice. The treatments comprised glufosinate ammonium (0.50 kg ha^-1), carfentrazone-ethyl (0.02 kg ha^-1), 2,4-D Na salt (0.8 kg ha^-1), bispyribac-sodium (0.025 kg ha^-1) chlorimuron-ethyl + metsulfuron-methyl (0.004 kg ha^-1), chlorimuron-ethyl + metsulfuron-methyl combined with carfentrazone-ethyl (0.004 + 0.02 kg ha^-1) and alternative chemicals including sodium chloride (5 %), acetic acid (5 %), lime (0.1 kg m^-2), gypsum (0.1 kg m^-2), along with an untreated control. Observations on phytotoxicity, regrowth and biomass (fresh weight) at 20 days after spraying (DASP) revealed that carfentrazone-ethyl, glufosinate ammonium and a combination of carfentrazone-ethyl with chlorimuron + metsulfuron were effective in suppressing Pistia with 80 % drying or bleaching by 6 DASP. No regrowth of Pistia was observed by 20 DASP in these herbicides treated pots. Acetic acid induced rapid phytotoxicity, resulting in complete bleaching on the day of application. However, sodium chloride, lime and gypsum were ineffective in suppressing growth of Pistia. The most effective treatments were further evaluated in rice with Pistia to assess crop safety. Acetic acid and glufosinate ammonium caused significant crop injury to rice, while carfentrazone-ethyl demonstrated high efficacy against Pistia with no adverse effects on rice. The results identify carfentrazone-ethyl at 0.02 kg ha^-1 as a fast-acting, selective and environmentally safer option for managing Pistia in flood-prone lowland rice ecosystems.