March 21, 2008
The proliferation of glyphosate-based products into the glyphosate-resistant crop market is unprecedented. Currently, more than 50 glyphosate-based herbicides are registered for use in Nebraska. The influx of generic glyphosate-based herbicides resulted in lower initial prices as distributors attempted to remain competitive; however, this is not the case anymore and there are indications of a major increase in glyphosate prices. For example, generics that cost $10-12 a gallon last summer, might cost more than $20 a gallon this summer, while brand names that used to cost $40 a gallon might cost as much as $75 a gallon this season.
This resulted in many phone calls and questions from local producers interested in getting the best weed control for the lowest cost. The following story reports on a study that compared efficacy of a variety of glyphosate-based products (generic and brand names) on weed control over three years at six locations in Nebraska. Weed species composition in our studies included: velvetleaf, common waterhemp, sunflower, kochia, Russian thistle, lambsquarters, and a mix of foxtail species. Depending on the year or location, we tested these glyphosate-based products at two rates (label rate and half-rate): Roundup Ultra®, Roundup UltraDRY®, Roundup UltraMAX®, Roundup WeatherMAX®, Touchdown w/IQ®, Cornerstone®, Clearout 41 Plus®, GlyphoMAX®, Glyfos Xtra®, and Glyphomax Plus®.
All herbicides provided excellent weed control (> 90%) regardless of the rate or brand name. For example, there was no significant difference in the level of weed control for a brand name Roundup Ultra Dry when compared to the generic product Clearout41 Plus. Similarly, the level of weed control was not significantly different for the brand name product Roundup WeatherMax when compared to the generic product Clearout 41 Plus or any other herbicide tested.
These findings were similar to results reported by our colleagues from other states. Therefore, generic glyphosate-based products can provide a valuable tool for weed control in glyphosate-tolerant crops, especially for those producers who are interested in lowering crop production inputs by reducing weed control costs. Producers may want to focus on herbicide costs, the appropriate herbicide rate for the weeds present, and environmental factors rather than the trade name of the glyphosate product. As the price of glyphosate increases, growers may want to consider using a preemergence residual/postemergence glyphosate herbicide program rather than a two-pass postemergence glyphosate program as a foundation in corn and soybeans. With increasing glyphosate prices, the economics of preemergence residual herbicides becomes more favorable. Incorporating the use of other modes of action can reduce the potential for the development of glyphosate-resistant weed biotypes. Residual preemergence herbicides also can help maintain an appropriate "weed free window" to protect yield potential and provide flexibility in the timing of postemergence applications.
With the increased acres of Roundup-Ready corn, and growing use of glyphosate-based products there is an even greater need for their proper use. Their value can be preserved only by proper management and reduced overuse. It is easy to fall into a trap of overusing glyphosate when one glyphosate-resistant crop is grown after another. Proper use of glyphosate-based technology, as a component of an integrated weed management program, is the key to preserving the long-term benefits of this technology, while avoiding many of the concerns about its use, or misuse. For more details about proper use of herbicide-tolerant crops see NebGuide 1484, Use of Herbicide-tolerant Crops as a Component of an Integrated Weed Management Program.
Stevan Knezevic
Extension Integrated Weed Management Specialist
Haskell Ag Lab, Concord
Lowell Sandell
Extension Educator, Weed Science
