Recommendations for successful establishment of Roundup Ready alfalfa

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.  

Establishing productive Roundup Ready (RR) alfalfa stands require close attention to details, especially when the plants are young. An early-season application of glyphosate will significantly help alfalfa establishment in two ways. First, glyphosate will remove many of the weed seedlings competing with the new alfalfa seedlings for nutrients and space. By targeting weeds when they are small, excellent control can be expected for almost all weed species.

The second reason for an early application of glyphosate in RR alfalfa is to remove the alfalfa seedlings that do not have the glyphosate-resistant trait. As new alfalfa stands mature, natural thinning takes place, which reduces the total number of alfalfa plants. As surviving plants grow, they fill empty spots in the crop canopy until a healthy, productive alfalfa stand is established. In a typical bag of RR alfalfa seed, a small portion of the seeds do not carry the glyphosate-resistant trait. These seeds will germinate and grow into plants indistinguishable from the glyphosate-resistant alfalfa plants. If an application of glyphosate is made, the non glyphosate-resistant plants will be controlled. By applying glyphosate early in the development of an alfalfa stand, the susceptible plants are removed, allowing the glyphosate-resistant plants to remain . Delaying the application of glyphosate will increase the chance of a non glyphosate-resistant alfalfa plant becoming an established plant in the alfalfa stand. When this occurs, the susceptible plant will suffer severe injury and/or death after the first application of glyphosate, leaving an empty spot in the stand . These open areas allow weeds to become established, possibly leading to reductions in yield and alfalfa quality.

MSU recommends applying glyphosate at a rate of 0.75 lb ae/A before the 4 th trifoliate growth stage to eliminate seedlings not containing the glyphosate-resistant gene. This practice encourages the development of a health population of RR alfalfa plants and prevents susceptible plants from becoming established. When making any pesticide application, always read and

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