Monsanto says it has dropped its plan to acquire crop science rival Syngenta. Monsanto first approached Syngenta in early May with an offer worth $45 billion but was rejected by the Swiss firm. It came back in June offering a $2 billion payment if the deal didn’t go through but was again rejected. Its latest bid, made earlier this month, raised the offer by about 5%. In rejecting Monsanto yet again, Syngenta said the offer “significantly undervalued the company and was fraught with execution risk.” Both firms say they will proceed as stand-alone companies.