Control of Emerging Weeds In Cotton and Wheat Minimium Tillage Systems In the Southern Rolling Plains.

Reduced tillage and the adoption of glyphosate tolerant cotton (Gossypium hirsutum) varieties have resulted in a weed shift to certain perennial glyphosate tolerate weeds and the potential for glyphosate resistant weeds in the US southern plains.  New weed control strategies or the re-adoption of former weed control methods are needed to improve and prolong the benefits of reduced tillage and glyphosate tolerant crops.   Emerging and re-emerging problem weeds in the US southern plains include: prickly pear (Opuntia spp.), mesquite (Prosopis spp.), various native and introduced perennial grasses (Chloris spp., Tridens albescens, Nassella leucotricha, and Bouteloua dactyloides), volunteer cotton (Gossypium hirsutum), field bindweed (Convolvulus spp.), hog potato (Hoffmanseggia densiflora), globe mallow (Sphaeralcea ambigua), Guara (Guara spp.) and others.   Applied research trials established in 2010 and 2011 in Central Texas evaluated multiple herbicides and rates for efficacy and development of control recommendations. Trials to fallow fields were established in the fall of 2010 to evaluate different rates of glyphosate and glyphosate mixed with other broadleaf herbicides for their control of native and introduced perennial grasses and other weeds.  High rates of glyphosate, exceeding twice the normal rate; provided superior control among the treatments but did not provide complete control.  A trial established and evaluated in the spring of 2011 pre-plant to strip-till cotton in a wheat (Triticum aestivum)/cotton rotation, comparing rates and combinations of glyphosate and clethodim; provided similar results.