Better weed control was the top reason growers bought Roundup Ready alfalfa seed, according to the University of California (UC) survey on the transgenic crop. After conducting trials on it, survey co-author and UC farm advisor Steve Orloff says glyphosate is very effective on problematic weeds such as dodder and some perennials.

“Regardless of how you feel about genetically engineered alfalfa, most people would have to agree that glyphosate, or Roundup, is the most effective broad-spectrum post-emergence herbicide developed. It’s very effective, especially in seedling alfalfa,” he told Western Alfalfa & Forage Conference participants.

Dodder has been a worrisome weed in alfalfa. Although dinitroani-line herbicides give effective pre-emergence control, it’s rarely perfect, added Orloff. Roundup controls dodder that’s already attached to alfalfa.

“In the Intermountain area, we have stand lives of six, seven, eight years. We have a horrible problem with perennial weeds like dandelion. Roundup works very well on it.” It also controls quackgrass, another problematic weed there, he said.

“Probably the main concern when it comes to weed control in Roundup Ready alfalfa is the evolution of resistant weeds. What we need to do as alfalfa growers is learn from the other Roundup Ready crops.

“And it’s not just Roundup Ready alfalfa growers, but also growers who are using Roundup in other crops. If they don’t do a good job of using integrated weed-control programs and alternating herbicides, you could have a problem with their Roundup-resistant weeds. It’s incumbent on all producers of Roundup Ready crops to employ a diversity of weed-management systems and not rely solely on glyphosate for a weed-management system,” Orloff said.