Is All Glyphosate Created Equal?
The proliferation of glyphosate products into the Roundup® Ready crop arena has taken the generic herbicide market to a new level. No matter how many herbicides are introduced, the question always comes
back to: will glyphosate in product X perform as well as glyphosate in product Y? Soybean and corn field studies were conducted for three years in five locations across Nebraska to evaluate different brands of glyphosate herbicides. In 2001 and 2002, equivalent rate treatments of 16 and 32 ounces per acre of the glyphosate products Roundup® UltraMax, Roundup® Ultra, Roundup® WeatherMAX, Roundup® UltraDry, Touchdown®, Clearout® 41 Plus, Glyfos® Xtra, Cornerstone®, Glyphomax®, and Glyphomax® Plus were applied. In 2003, treatments were reduced to 12 and 24 ounces per acre. Ammonium sulfate (AMS) was added to all treatments at a rate of 17 lbs/100 gallons. Most of the products represent the isopropylamine (IPA) salt of glyphosate; however, Touchdown® is formulated as the diammonium salt of glyphosate, Roundup® UltraDry is formulated as the mono-ammonium salt of glyphosate and Roundup® WeatherMAX is formulated as a potassium salt of glyphosate. All sites were evaluated for percent control of both grass and broadleaf species at 10-15 and 25-30 days after treatment.
Over the three year time frame, differences were small and varied slightly across the different trade names in the glyphosate tolerant soybean and corn treatments. Control remained similar across the different locations in wheat stubble, with few significant differences between products at either rate. As a whole, few differences were seen among the different glyphosate brands in this study across the locations, especially in row crop situations. With a difficult to control species, such as barnyardgrass, or in a more demanding climate, such as western Nebraska, differences are easier to find although they will be random and varied. In most climates there seems to be little or no differences between brands. Rate, environmental factors, and cost will most likely play a larger role in the decision process than brand name. In addition, service may be an important factor to a producer. The most important two factors are knowing whether to add surfactant and always adding AMS to your glyphosate. The glyphosate product label will tell you if “no surfactant is needed,” “you may add surfactant” or “you must add surfactant.” The “no” and “must” statements are easy to understand but the “may” statement is confusing. “May” means that your glyphosate product contains some surfactant but that this may not be enough in the right environmental situation. If you are spraying tall weeds or are in very dry conditions, adding 0.25% (1 quart/100 gallons) surfactant to the glyphosate tank may be beneficial. Ammonium sulfate will help combat hard water problems and improve glyphosate’s efficacy. Always add at least 8.5 lbs per 100 gallons or the equivalent 1% rate for liquid AMS. As you sort through the glyphosate products be sure to find out the surfactant load situation, plan to add AMS, and choose a product with which you are comfortable. (UN Crop Watch News Service, 6/18/04).
Ed.s note: Although this article refers to Roundup® Ready Crops, the glyphosate recommendations are appropriate to anyone using large amounts of glyphosate.
