The high value of cotton and the high risk of yield loss from weeds, especially from the continued threat from glyphosate resistant pigweed and marestail, has helped spur the use of Liberty Link cotton varieties in the upper Southeast.

Some farmers have found they can get similar results on weed control by using Phytogen varieties that contain the Widestrike gene for insect control and spraying this cotton with Ignite herbicide.

While it’s legal, it’s high risk and not a practice encouraged by either Bayer, which markets Ignite herbicide as part of their Liberty Link system of cotton varieties or Dow, which markets Phytogen brand cotton seed that contain the Widestrike gene for insect management.

WideStrike Insect Protection is a two-gene, in-plant trait that provides broad spectrum and season-long control of lepidopteran insect pests, such as fall armyworms.

The LibertyLink Cotton System is a new transgenic,postemergence herbicide management system for cotton developed by Bayer CropScience.

LibertyLink cotton varieties marketed by FiberMax have a genetically based resistance to Ignite herbicide (also called Liberty, Finale and Rely).

Glufosinate ammonium is the herbicide used in LibertyLink cotton and other crops. If applied on plants that contain a gene for tolerance, the herbicide does a good job of controlling a wide spectrum of weeds without damaging cotton plants.

As part of the research and development and subsequent manufacturing process for Widestrike cotton, a gene similar to the gene used to provide tolerance to glufosinate is used as a genetic marker. Thus, Widestrike cotton does have some built in genetic tolerance to glufosinate.

In producing Widestrike cotton seed, there is no easy way to turn insects on or off to determine whether the selected gene that provides insect protection is active. By including a gene similar to the LibertyLink gene, researchers can spray cotton plants and if the plant dies, they know the Widestrike gene was not passed on to target seed.

Mostly by accident, and often serendipitously, some cotton growers found they could take a shortcut and use Widestrike-containing Phytogen varieties and spray them with glufosinate.

LibertyLink on Widestrike is a legal application and it usually works. However, the practice is not recommended by university Extension weed specialists and is not supported by either Dow AgriScience or Bayer AgriScience.

Dow AgriScience has made public its stance on using glufosinate or Liberty Link on Phytogen varieties containing the Widestrike gene noting:

• The tolerance provided by the PAT gene in Widestrike cotton is not equivalent to the glufosinate tolerance gene found in Liberty Link-containing varieties.

• Though legal to apply over-the-top applications of ammonium-containing herbicides on Widestrike cotton, this practice may result in crop damage or loss.