Bayer AG unit Monsanto Co. won’t have to face a class action alleging it falsely advertised Roundup by saying the weed killer’s active ingredient, glyphosate, doesn’t affect humans or pets.

Individual questions about whether proposed class members relied on the herbicide’s label make class certification inappropriate, the U.S. District Court for the Western District of Wisconsin ruled Jan. 2.

Bayer, which acquired Monsanto last year, faces suits by some 8,700 people who blame their cancer on Roundup.

In this consumer...