New Herbicide-tolerant Trait Technologies Are Another Tool

Wednesday, December 24, 2014

There are two new herbicide-tolerant trait technologies nearing commercialization. According to Kevin Bradley, University of Missouri weed scientist, they are another tool for weed control but are not a one-shot answer to weed control.

One is Dow Agrosciences' Enlist Weed Control system. The system offers corn and soybean tolerance to glyphosate and 2,4-D choline. The trait additionally allows the use of glufosinate (Liberty) in soybeans and cotton. The enlist traits and herbicides are fully deregulated in the U.S., but the company is waiting for Chinese approval before a full commercial launch.

Monsanto's new Xtend technology will allow the use of glyphosate and dicamba in soybeans and dicamba, glyphosate and glufosinate in cotton. Deregulation is expected in 2015 on the Roundup Ready Xtend Crop System. Monsanto has said it will not launch the soybean trait until it receives import approval from China, but plants a limited release of cotton in 2015 upon clearing regulatory hurdles.

Both of these traits are not a stand alone management strategy for resistance weed management. However, when used in conjunction with pre-emergence residual herbicides, rotating modes of action, and scouting and monitoring of weed populations, they provide a another option in managing resistant weed populations.

Both Xtend and Enlist technology have been marketed as containing multiple modes of action. One of the limitations is one component (glyphosate) of the new herbicide premixes is already compromised by the herbicide resistance of waterhemp, ragweed and Palmer Amaranth. Growers that spray glyphosate resistant weeds with only the Xtend or Enlist-compatible herbicides are essentially relying on one mode of action. Without a pre-emergence herbicide, you are putting all of the pressure on 2,4-D or dicamba.

The new herbicide-tolerant traits will deliver the most value as pre-plant applications with no plant back restrictions. Producers will be able to burn down spring populations of marestail, ragweed and winter annuals without fear of burning herbicide-tolerant crops. Producers should not rely on dicamba as a residual. The residual activity or dicamba is highly variable and depends on rainfall. In dry conditions, it can last as long as two weeks, but with good moisture after application, dicamba will be quickly metabolized in a matter of days.

One concern with these new technologies is the potential for drift when these technologies come to market. There will be an abundance of non-tolerant crops to this technology. Not only can it affect field crops but other significant crops such as grapes, orchards, tobacco farms and urban areas. Windspeed during application will be critical. Follow the company recommendations to triple rinse your sprayer. Tank clean out tests showed that after a dicamba application, a sprayer needed three full rinses before non-resistant soybean sprayed with the rinse water yielded the same as controls.