1970 — Monsanto developed glyphosate as an herbicide in 1970. The company patented glyphosate as a weed killer in 1970 and kept the patent until 2000.
Reference: Moncivais, Katy. “Roundup Cancer Lawsuit: 2020 Updates & Settlements.” Consumer Safety, 8 Jan. 2021, https://www.consumersafety.org/product-lawsuits/roundup/