Managing Weeds in No till Systems to Overcome Resistance Weeds in the Southeastern U.S.

Glyphosate-resistant weeds are now present throughout the Southeast.  Hundreds of thousands of conservation tillage cotton acres, some currently under USDA Natural Resources Conservation Service (NRCS) conservation program contracts, are at risk of being converted to higher-intensity tillage systems.  The shift to higher-intensity tillage facilitates seed burial as well as preplant incorporated and pre-emergence herbicide control of this problematic weed, especially in dry-land cotton production.  Conservation tillage has been recognized as a beneficial alternative to conventional tillage practices, but adoption remained sluggish through the ‘80s and mid ‘90s due, in large part, to poor weed control and weed control options available for these systems. A turning point was reached when, in 1996, Monsanto introduced Roundup Ready^® soybean and subsequent glyphosate-resistant crops offered a successful alternative to conventional weed management that could be incorporated into conservation agriculture systems. Best management practices recommend rotating crops and chemicals to avoid the development of resistance. Unfortunately many producers have had little economic opportunity to grow different crops for a number of reasons. In addition, the system of glyphosate-resistant crops has become so prevalent that rotation of crops does not ensure that chemical weed control choice will change along with a change of crops. It is not surprising that resistance to a single chemical would appear under these conditions. Much research has focused on controlling this problematic weed.  An abbreviated list of the solutions offered includes: crop rotation intensification (including pasture-based rotations), improving residual herbicide performance in dry-land conservation systems, weed management intensification (scouting, timely applications, etc.), and integration of cultural solutions (high residue cover crops, delayed planting, etc.).