Donnie K. Miller, P. Roy Vidrine and Alexander M. “Sandy” Stewart
The 21st century has provided producers with a number of technological advances that affect all aspects of cotton production. The overwhelming acceptance of Roundup Ready and Bt technologies on weed and insect management strategies demonstrates their positive effects. In addition to Roundup Ready cotton, a second transgenic system commercialized as Liberty Link technology offers producers the ability to control a broad spectrum of grass and broadleaf weeds that commonly infest cotton.
Like its transgenic counterpart, the Liberty Link system’s potential benefits include reducing or eliminating chemical applications or tillage operations and controlling a broad weed spectrum. This technology also offers rotational flexibility to plant other crops because glufosinate – the active ingredient in Ignite, the herbicide labeled for use in this system – has no residual soil activity.
Similar to how the second generation of Roundup Ready cotton – termed Roundup Ready Flex – responds to the herbicide glyphosate, Liberty Link cotton exhibits excellent overthe- top (direct spray contact) tolerance to Ignite regardless of crop growth stage. This places less reliance on specialized spray equipment intended to reduce herbicide-plant contact and allows the use of larger, faster-moving application equipment during the growing season. This also may provide the opportunity to co-apply insecticides with Ignite, thereby reducing application trips through the field. Crop Tolerance, Weed Control
Research conducted with Liberty Link cotton by LSU AgCenter weed scientists has focused on crop tolerance, weed efficacy and co-application effects. The lack of visual injury or negative growth effects with over-the-top Ignite application indicates excellent crop tolerance to the herbicide. Efficacy trials indicate excellent season-long control of most broadleaf and grass weeds in cotton when Ignite is applied to small (1- to 3-inch-tall), actively growing weeds. Ignite should be applied as early as possible once weeds emerge because delaying initial application may result in early-season weed competition that may reduce yield. In addition, Ignite acts primarily as a contact herbicide, so it requires thorough weed coverage, which is especially important in dense weed populations.
Although Ignite provides excellent control of most weed species, control of broadleaf Amaranthus or pigweed species and goosegrass can be erratic, especially with larger plants. In such situations where heavy pigweed pressure exists, including soil-residual herbicides (DNA herbicides, Dual Magnum or Staple LX) at planting to prevent weed emergence or co-applying Staple LX with Ignite to control existing weeds or provide soil-residual control has proved beneficial in a Liberty Link system. In addition, adding Dual Magnum to Ignite can provide soil-residual pigweed control into the growing season.
For heavy goosegrass pressure, applying DNA herbicides or Dual Magnum at planting offers the best option because Ignite can be antagonistic (reduce control) when co-applied with grass herbicides after weed emergence. Grass herbicide must be applied three days before or seven days after an Ignite application to reduce potential antagonism. Research has also shown that including additional herbicides with residual soil activity at planting can buy producers time in making the initial Ignite application and limit weed competition that can occur when the initial application is delayed by weather and weeds become larger. Additional Benefits
Perhaps the main benefit of including other herbicides in a Liberty Link system is to introduce different modes of action to prevent weed resistance associated with the continuous use of Ignite. Each producer must determine the need for additional herbicides depending on the weed spectrum, the producer’s ability to cover his acreage in a timely fashion to eliminate early-season weed competition, environmental factors that affect timeliness of application, increased costs associated with the new technology and the cost efficiency of using additional inputs.
Research conducted on weed control with Ignite co-applied with most cotton insecticides indicated no negative effects on control of most of the common weed problems in cotton in Louisiana.
Although increased costs are associated with this new technology compared with conventional varieties, producers may feel that the opportunity to use larger, faster-moving equipment and reduce the number of application trips through the field by co-applying insecticides with Ignite in over-the-top applications more than offset the increased cost. In addition, both Liberty Link and Roundup Ready Flex offer the potential to be used as highly effective alternate weed control systems in a weed-resistance management program.(This article was published in the winter 2007 issue of Louisiana Agriculture.)