There is one small field on Michael Sullivan’s farm, near the town of Burdette, Ark., that he wishes he could hide from public view.

The field is a disaster. There are soybeans in there, but you could easily overlook them. The field has been overrun by monsters: ferocious-looking plants called pigweeds, as tall as people and bursting with seeds that will come back to haunt any crops that Sullivan tries to grow here for years to come.

“I’m embarrassed to say that we farm that field,” Sullivan says. “We sprayed it numerous times, and it didn’t kill it.”

These weeds have become resistant to Sullivan’s favorite herbicides, including glyphosate, which goes by the trade name Roundup.

Yet the rest of Sullivan’s farm is beautiful. As farmers like to say, the fields are “clean.” There is not a weed to be seen.

In those fields, he planted soybeans that enjoy a novel superpower. They’ve been genetically modified by Monsanto, the biotech giant, so that they tolerate a different weed-killing chemical, called dicamba.