To prevent future weed-control problems, Roundup Ready alfalfa growers need to use a herbicide other than glyphosate sometime during the life of the stand, stresses Dan Putnam, University of California Extension forage agronomist.

“We really would like to see growers adopt a more integrated weed-management approach, which includes rotation of herbicides, crop rotations and other techniques to reduce the development of weed populations that are resistant to Roundup,” says Putnam. “If somebody adopts a purely Roundup Ready system, weed resistance or weed shifts eventually will occur.”

For more information, download the pdf version of the University of California publication, Avoiding Weed Shifts and Weed Resistance in Roundup Ready Alfalfa Systems.

Crop and herbicide rotation are critical, agrees Dan Undersander, University of Wisconsin Extension forage agronomist. In fact, he says crop rotations are also the most profitable because low-yielding stands are turned over, legume credits are available for the next crop and other rotational benefits increase the yield of the following crop.

But growers also need to make sure the Roundup Ready trait doesn’t leave their fields. “Both types of stewardship are important,” says Undersander.

“You need to plant the seed in the field you intend to and in the Midwest it will stay there,” he says. “It’s important to point out that we really haven’t seen that the Roundup Ready gene will spread from hayfields. Plants aren’t going to last in a hayfield long enough to produce mature seed because that doesn’t occur until four to six weeks after flowering.”