The availability of Roundup Ready alfalfa adds another tool to the toolbox in the battle for high-quality alfalfa, says Peter Thomison, Ohio State University Extension agronomist. Before planting it, though, he says growers should compare the need for glyphosate for weed control vs. the added seed cost.

“Consider your goals and the importance of weed-free alfalfa in your particular situation,” Thomison advises.

“Glyphosate may be especially helpful during stand establishment because it causes less injury to seedling alfalfa than most other herbicides used during stand establishment,” he adds. “It also controls a broader range of weeds than other alfalfa herbicide options.”

Ohio State participated in a five-year study evaluating Roundup Ready alfalfa across six states. Glyphosate was compared with an alternative herbicide program and a no-herbicide check. At all locations, glyphosate controlled weeds with no crop injury during the establishment year, Thomison reports. Controlling weeds with either glyphosate or alternative herbicides resulted in greater alfalfa yield and greater forage quality compared with not using herbicides. Controlling weeds increased crude protein content by three percentage units and decreased NDF by 3.8 units, on average, across all locations in the seeding year.

During the seeding year, the alfalfa yield was 0.44 ton/acre higher in the glyphosate treatment than in the alternative herbicide treatment, but total forage (alfalfa plus weeds) yield and forage quality were the same.

Herbicides were not needed for weed control after the seeding year at most locations, even into the fifth year. The alfalfa stand was vigorous and provided sufficient competition to keep weeds from re-invading for the remainder of the stand life, says Thomison.

“Keep in mind that those studies were conducted with small-plot equipment so wheel traffic was not an issue,” he says. “Under normal farm production practices, alfalfa stands tend to be weakened by wheel traffic and weeds can re-invade sooner than under experimental plot conditions. This is particularly true with the large equipment used on many farms today. The Roundup Ready technology will be especially useful where troublesome perennial weeds take hold later in the life of the stand. Examples include thistles, curly dock and dandelion, which are hard to control with other herbicides labeled for alfalfa. Winter-annual weeds can also be controlled well by glyphosate.”

Opponents of Roundup Ready alfalfa are concerned that it might contaminate organic and conventional alfalfa seed production and increase the occurrence of glyphosate-resistant weeds. When USDA deregulated the crop in January, it concluded that those issues were not of sufficient impact to justify placing restrictions on the crop’s use.

“Glyphosate tolerant alfalfa should be grown judiciously because of the risk of developing glyphosate-resistant weeds,” says Thomison. “Resistant weeds are likely to develop more rapidly if glyphosate is used on all crops. Just as crop rotation is important, so is rotation of herbicide chemistries. In addition, some customers won’t buy genetically engineered crops, so you need to know what your customers will accept.

“As genetically modified alfalfa use increases, we will learn the degree to which glyphosate-tolerant genes occur in conventional and organic alfalfa. In the USDA’s Record of Decision, this and other concerns are discussed in detail. I hope the concerns with contamination by genetically modified alfalfa can be adequately addressed so conventional and organic alfalfa production can continue without undue additional cost and effort by producers choosing those systems.”

He encourages growers who decide to plant Roundup Ready alfalfa to read USDA’s Record of Decision.

“Be informed and use this technology wisely as part of an overall well-managed system,” he advises. “Respect your neighbor’s desire and right to produce organic crops on his/her farm and work together so both of you can achieve your goals.”