It’s a more intensive version of the same approach that made the resistant superweeds such a problem — and some scientists think it will fuel the evolution of the worst superweeds yet.

These weeds may go a step further than merely being able to survive one or two or three specific weedkillers. The intense chemical pressure could cause them to evolve resistance that would apply to entire classes of chemicals.

“The kind of resistance we’ll select for with these kinds of crops will be different from what we’ve seen in the past,” said agroecologist Bruce Maxwell of Montana State University. “They’ll select a kind of resistance that’s more metabolism-based, and likely resistant to everything.”

 

Next-generation biotech crops erupted into controversy with the U.S. Department of Agriculture’s ongoing review of Enlist, a Dow-manufactured corn variety endowed with genes that let it tolerate high doses of both glyphosate, an industry-standard herbicide better known as Roundup, and a decades-old herbicide called 2,4-D.

Back in the mid-1990s, when so-called Roundup Ready seed strains first allowed farmers to spray the herbicide directly onto fields without fear of damaging crops, 2,4-D and other older chemicals were already falling from favor. They were more toxic and less effective than glyphosate, and farmers gladly replaced them with a single all-purpose treatment.