For 30 years glyphosate has kept morningglories, a noxious weed that can lower yields and choke harvesters, out of farm fields. But something is changing.

For the first time, University of Georgia (UGA) researchers have identified morningglory families that are tolerant to glyphosate.

“Our study suggests that serious and immediate consideration should be given to developing regional strategies for managing the evolution of tolerance in morningglories,” says Regina Baucom, a UGA doctoral student who directed the research. Baucom and UGA assistant professor of genetics Rodney Mauricio co-authored the study.

Glyphosate is a relatively recent tool in the fight against weeds. This fact has led the scientists to conclude that the tolerance trait in this wild population was naturally occurring, not caused by use of the herbicide.

The problem is that the chemical does kill most morningglories effectively, so the tolerant ones could be the “last weed standing,” leaving farmers without an effective means of control.

Glyphosate has been available since 1974. But to date, only six cases of glyphosate resistance in plants have been reported among the 250 documented cases of herbicide resistance, the researchers say.

“Our interviews with farmers in the Southeast suggest that morningglories can tolerate applications of glyphosate,” Baucom says. “And, in some cases, increasing concentrations of the herbicide have been required to control it.”

What Baucom and Mauricio found was that, in at least one natural population of morningglories they studied, there is a substantial genetic variation for tolerance, meaning that the “evolutionary door” is wide open.

Morningglories aren't at the level of such nuisance weeds as musk thistles in crops, but they're still a widespread problem for farmers. The new evidence for genetic variation of tolerance in morningglories, however, points toward a potential problem with no easy solutions.

“For glyphosate, such strategies could involve something as simple as periodically spraying with alternate herbicides, as long as there is little cross-tolerance with glyphosate,” the scientists say.