Monosodium methyl arsenate (MSMA) is an arsenic-based herbicide and fungicide. It is an organic arsenate; but it is a less toxic organic form of arsenic, which has replaced the role of lead hydrogen arsenate in agriculture. It is one of the most common herbicides used on golf courses. It is typically used for control of grassy weeds such as crabgrass. Another common use is for burning the marked lines into grassy sports fields.
Some of its trade names include Ansar 170, Ansar 170L, Ansar 529, Ansar 529 HC, Ansar 6.6, Asazol, Bueno, Bueno 6, CCRIS 4676, Caswell No. 582, Daconate, Daconate 6, Dal-E-Rad, Dal-E-Rad 120, Drexar, Gepiron, HSDB 754, Herb-All, Herban M, Merge, Merge 823, Mesamate, Mesamate H.C., Mesamate-400, and Mesamate-600.