Food safety activists have promised to fight the crops—corn and soybeans designed to tolerate multiple herbicides—in court. They and many scientists argue that these crops will harm environmental and possibly human health. The companies that make them say they're providing a much-needed tool to fight the growing scourge of herbicide-resistant weeds.

Lawsuits aside, these crops and others like them may force a showdown between conflicting approaches to farming: one that depends on chemicals to fight weeds, and another that embraces ecology's lessons.

"We are on the brink of a crisis situation," said Neil Harker, a weed ecologist with Agriculture and Agri-Food Canada, the Canadian equivalent of the US Department of Agriculture. "I do consider right now to be a watershed, direction-defining moment for agriculture."