Glyphosate-resistant marestail identified in South Dakota,US

In 2010 glyphosate-resistant horseweed, or marestail, was identified in South Dakota,US, which did not come as a big surprise to plant scientists explained, Paul O Johnson, SDSU Extension agronomy field specialist.

"This did not come as a big surprise because horseweed was the first broadleaf weed found to be resistant to glyphosate in the United States," said Johnson of the resistant horseweed found in Delaware in 2000 in a no-till situation.

Johnson explained that the reason horseweed is hard to control is that it has shown that it can germinate early in the spring, form a rosette, vernalize and produce seed that same year.

Johnson encourages growers to look beyond chemical control when it comes to controlling horseweed.

"Although when we look at dealing with resistance, chemical control is often the first thing considered because it is appears to be less work, but there are also some other ways to manage resistant horseweed," he said.

Some of the Ways Include:
Tillage: Tillage done in fall or early spring will provide excellent control;

Crop rotation: Crop rotation, independent of chemical treatments, can also help to control this weed;

Planting spring wheat or winter wheat: Both of these crops provide ways to control this weed with chemicals;

Planting corn or sorghum: Corn or sorghum both have other chemical options that can control glyphosate resistant horseweed;

Rotating to a perennial crop like alfalfa: By providing permanent cover to keep the horseweed from germinating, this can provide good control.

Johnson explained that considering an integrated approach is important when dealing with all resistance.
"By looking at more than one control strategy it should be easier to eliminate the problem and avoid more resistance problems in the future," he said.