By Mark Sulc, Forage Extension Specialist, The Ohio State University
In January, the U.S. Department of Agriculture announced the deregulation of Roundup Ready alfalfa after a 46-month environmental impact assessment process. The ruling means that U.S. farmers are free to proceed with planting the genetically altered alfalfa with no restrictions.
Opponents to this ruling have been vocal in their disapproval. They have voiced concerns that without any restrictions the biotech alfalfa will easily contaminate organic and conventional alfalfa seed production and increase the occurrence of glyphosate-resistant weeds. Based on their response, further court battles over this product may be in store.
Whether you agree or disagree with this decision, the fact remains that Roundup Ready alfalfa has been approved for planted this spring. For those considering use of this new technology, what factors should be considered? Where might Roundup Ready alfalfa be of benefit?
We know that good managers have been able to control weeds in alfalfa to acceptable levels with current herbicides and best management practices for years. We also know that glyphosate is effective on many types of weeds, so it adds another tool to the toolbox in the battle against weeds in alfalfa. Glyphosate may be especially helpful during stand establishment because it causes less injury to seedling alfalfa than most other herbicides labeled for establishing that crop. So seedling stands of alfalfa should develop faster with less injury when glyphosate is used instead of other herbicides.
We participated in a 5-year study of Roundup Ready alfalfa conducted across 6 states from 2006 to 2010. At all locations, glyphosate was used to control weeds in the establishment year, and it did an excellent job of weed control with no crop injury. 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 3 percentage units and decreased NDF by 3.8 units.
During the seeding year of our study, alfalfa yield was 0.44 ton per acre higher in the glyphosate treatment than in the alternative herbicide treatment, but total herbage yields and forage quality did not differ between the herbicide treatments. After the seeding year at nearly all locations, no herbicides were needed for weed control, even into the fifth year of the stands. The alfalfa stands were vigorous and provided sufficient competition to keep weeds from re-invading for the remainder of the studies.
Keep in mind that these studies were conducted with small plot equipment where wheel traffic was not an issue. Under normal farm production conditions, alfalfa stands tend to be weakened by wheel traffic, and weeds can re-invade sooner than under our experimental plot conditions.
So glyphosate or other herbicides are more likely to be needed to manage weed competition as the stand ages under farm production conditions. The Roundup Ready technology will be useful in those situations, especially where troublesome perennial weeds take hold later in the life of the stand. Examples of such perennial weeds include thistles, curly dock, and dandelions. Winter annual weeds can also be controlled well by glyphosate.
Roundup Ready alfalfa is being marketed by several companies. Based on variety testing results from trials established in 2006 before the ban on Roundup Ready alfalfa, the yield potential of Roundup Ready alfalfa varieties compared very well with conventional elite alfalfa varieties. Roundup Ready seed will be more expensive, so the benefits and need for glyphosate for weed control in your situation should be weighed against the extra seed cost to use this technology.
Roundup Ready alfalfa should be grown judiciously because of the risk of developing glyphosate-tolerant weeds. Resistant weeds are likely to develop more rapidly if we use, and only use, glyphosate 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.
Roundup Ready alfalfa will be a useful technology for some people but may not be for others. As genetically modified alfalfa use increases, we will learn whether the concerns regarding genetically modified organisms (GMO) contamination of conventional and organic alfalfa are valid and if they can be adequately addressed. I hope they can, because there are other GMO traits that potentially are very interesting for alfalfa producers. A good example is the development of alfalfa varieties with lower lignin, which are already being developed and have been shown to result in greater milk production in lactating dairy cows.
In summary, Roundup Ready alfalfa is here. If you decide to use this new technology, use it wisely as part of an overall well-managed system.