Glyphosate resistant horseweed or marestail
In the early nineties there was development of Su or Imi resistant then marestail. This weed being a fall annual found normally in no-till systems were very hard to handle if soybeans were planted. This was overcome in 1996 with the planting of Roundup resistant soybeans. This was a great fit until 2010 when the first glyphosate resistant now called horseweed was identified in South Dakota. This was not a big surprise because horseweed was the first broadleaf found to be resistant to glyphosate in 2000 in Delaware which was also in a no-till situation. It also has been found that horseweed can germinate early in the spring form a rosette vernalize and produce seed that same year.
When we look at the dealing with resistance, chemical control is the first thing looked at because it is easy. But this weed also can be controlled with tillage. Tillage in the fall or early spring will provide excellent control. Crop rotation can also help to control this weed. Spring wheat or winter wheat both provide ways to control this weed with chemicals. Corn or sorghum both have options that can control glyphosate resistant horseweed. Also rotating to a perennial crop like alfalfa so is a good option to control horseweed by providing permanent cover to keep the horseweed from germinating. One of the main characteristics to look at with all resistance is to take an integrated management approach for control. By looking at more than one control strategy it should be easier to eliminate the problem and avoid more resistance problems in the future.