Addressing Questions on Biotech Safety

Does the use of herbicide resistant crops create super weeds?

What is a super weed? A super weed, as it has been suggested by the popular press, is a weed that has become resistant to a particular herbicide. In recent years, the popular press has warned the public of the potential of herbicide resistance because of the wide-spread use of herbicides on herbicide-resistant biotech crops. Herbicide-resistant crops can be sprayed with a particular herbicide, killing weeds growing in and around the crop plants, without being damaged. Some examples include applying Roundup on Roundup Ready (glyphosate-resistant) soybean or applying Liberty on Liberty Link (glufosinate-resistant) corn. Herbicide resistance in weed plants is not new. Weeds have developed resistance to herbicides as early as the 1950s, long before herbicide-resistant biotech crops were on the market. It is possible that the application of herbicides to biotech crops could increase populations of herbicide-resistant weeds. However, virtually all herbicide applications have the potential to produce resistant weed populations, whether a biotech crop is involved or not.

Are herbicide-resistant weed populations a big deal? Herbicide-resistant weeds are more likely to be an issue where herbicides are used frequently for weed management (agricultural land, golf courses, etc.). Herbicide resistance is a result of heavy reliance on herbicides with the same mode-of-action as the primary method for weed management. With continued use of the same herbicide mode-of-action, weed populations resistant to a particular herbicide can increase dramatically over time.

In most situations there are a number of options available for weed management. Crop rotation can break the life-cycle or change the competitiveness of herbicide-resistant species. A different herbicide may be used to control resistant weed populations. Mixing two or more herbicides with different modes-of-action is another option. Tillage can also be an effective tool for weed management. The best weed management practices encompass a term known as IWM (integrated weed management). Integrated weed management involves using a number of strategies to effectively control weeds, not relying on any single option.

The benefits provided by herbicide-resistant biotech crops can potentially have a big impact on weed management. Protecting yield and preventing the spread and persistence of weed species are the main reasons for herbicide applications. Biotech crops allow us to use herbicides and specific weed management options that are not possible with conventional crops. The use of biotech crops and the respective herbicide application can save producers time and provide a highly-effective means of controlling weed populations. Using integrated weed management strategies when planting herbicide-resistant biotech crops can help insure that resistant weed populations remain at a minimum.

For a comprehensive list of resistant weed populations around the world visit

Content provided by Aaron Waltz, Weed Science Department UNL

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