In a big win for Monsanto Co., a federal judge in San Francisco has bifurcated the first bellwether trials in the multidistrict litigation over the herbicide Roundup, the first of which starts next month.

U.S. District Judge Vince Chhabria of the Northern District of California ruled Thursday that three upcoming trials would each have two phases. The first would focus on whether Roundup’s key ingredient, glyphosate, caused a plaintiff’s diagnosis of non-Hodgkin’s lymphoma and, if so, how much the jury should award in compensatory damages. The second, if needed, would address Monsanto’s liability and punitive damages.