Veteran North Carolina Weed Scientist Allan York calls glyphosate resistant Palmer pigweed the biggest threat to cotton since the boll weevil.
Combined with low prices, high production costs and a plethora of other problems, cotton acreage has plummeted by 30-40 percent across the upper Southeast, reaching 60-70 percent in some areas.
Though new technology and new varieties aren’t the cure all for cotton production in the Southeast, some of the new ones in the pipeline are sure to make life a little better for growers, especially when dealing with tough to manage weeds like Palmer amaranth.
Though still in the research stage, new varieties double stacked with genes that allow growers to spray cotton with glyphosate and glufosinate have looked extremely good in tests, despite intense heat and drought. Likewise, improved varieties with two herbicide genes and improved bollguard technology are on the way.
Glufosinate is a non-selective contact herbicide with some systemic action. Translocation occurs only within leaves, predominantly from the leaf base to the leaf tip. Glufosinate-ammonium has been widely used worldwide for a number of years for control of perennial and annual broadleaf weeds and grasses.
Liberty Link varieties, containing the gene that makes these cotton plants tolerant to glufosinate, have been highly successful in the Southwest, but have had limited application in the Southeast, primarily because of the real or farmer perceived yield drag in these varieties.
Researchers are quick to point out that the loss in yield potential is due almost entirely to the parent stock in which the glufosinate gene is included. Yield drag is directly proportional to the number of breeding lines and germplasm used in developing these varieties, not by the technology that is included in them.
Indications are that the three major players in cotton variety development — Bayer, Monsanto and Syngenta — will develop new, improved varieties in which improved technology will be included.
Advances in agronomic capabilities of cotton varieties are advancing as rapidly as is gene technology. The result is sure to be some outstanding tools for Southeastern cotton growers. Some of the early fruit of this combination of agronomic traits and genetic technology will be available to growers in the next few years, but the best is further down the pipeline.
Plant breeders across the Southeast are constantly selecting plants for their agronomic potential. For example, taking highly productive cotton plants from desert production areas in the Southwest and crossing these with germplasm from highly production varieties grown in the Southeast. The heat and drought that dogged cotton farmers in 2007 provided an excellent environment to test new varieties for tolerance to a number of drought and heat related stresses.
The dawning of the genetic era for row crop farmers began in the late 1990s with the introduction of Roundup Ready varieties that revolutionized cotton production, especially in the Southeast. Combined with no-till and strip-till systems, Roundup Ready cotton and glyphosate tolerant genes inserted into other crops allowed growers to significantly reduce input costs and greatly expand acreage without adding costly labor and equipment.
In less than a decade the genetic modification of cotton, corn, soybeans and subsequently many other crops by Monsanto revolutionized the face of agriculture worldwide.
Whether subsequent technological breakthroughs will ever rival this dramatic change in how crops are grown is open for debate, but surely offer the best opportunity for growers to maximize yields and reduce crop input costs.
The first chink in the armor of genetically modified varieties came with the documentation that horsenettle was resistant to glyphosate. The 2005 documentation of glyphosate resistant Palmer amaranth created a much bigger concern for cotton growers in the Southeast. Increased herbicide cost to offset or fight onset of glyphosate resistance played a role in the decrease of cotton acreage in the Southeast in 2007
Despite the risk of resistance, glyphosate remains the most effective and economical herbicide available to growers and eliminating it from use in the Southeast is simply not an option for most growers.
By incorporating genetic resistance to highly efficient contact herbicides, like glufosinate, in the same seed as glyphosate, plant breeders give growers much more flexibility as to how and when to use these herbicides.
Glyphosate provides systemic action that is the best and most affordable material available for managing Palmer pigweed. Glufosinate, if applied early, when pigweed are less than seven inches tall, provides excellent burn down of these troublesome weeds.
Even if glyphosate resistance develops, proper use of glufosinate will help growers overcome the problem by eliminating pigweed before they have a chance to develop seed. In addition, the two herbicides used together provide a much broader spectrum of control. Big seeded morningglory, for example, which has long-eluded glyphosate control, is highly sensitive to glufosinate.
For growers who have documented glyphosate resistance in their cotton fields in 2007, researchers contend one strategy for management is to identify hot spots in which this problem occurs. Look at the Liberty Link varieties that performed best in the growers’ particular area of the Southeast and develop a rotation system with glyphosate and glufosinate or Roundup Ready and Liberty Link varieties.
A big risk to the spread of glyphosate resistant weeds, especially Palmer pigweed, is that these prolific seed producing weeds will develop resistance to PPO herbicides, which are currently the best conventional option for managing pigweed. So far, no resistance has been documented for pigweed resistance to this family of herbicides, but weed scientists across the South are urging growers to avoid over-use of these materials.
Most states have herbicide resistance management programs available to growers. One of the best sources of weed resistance management information is provided by the National Cotton Council. The NCC’s Weed Resistance Learning Module provides general resource information on cotton herbicides and a list of contacts in each state for producers who have questions on management practices, including planting.
For more information, call the NCC at 901-274-9030.
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