Chloroacetamide Tank Mixes with Pyrithiobac in Glyphosate- and Glufosinate-Based Herbicide Systems

Cotton development is slow and even more sluggish under cooler temperatures early in the growing season.  Although delaying herbicide applications for 4 to 6 weeks after emergence of cotton had no effect on yield in early competition studies, glyphosate-resistant (GR) Palmer amaranth left uncontrolled for that period of time would be too large for adequate kill by available herbicides.  Therefore, residual herbicides in combination with postemergence (POST) herbicides are critical to achieving season-long control of Palmer amaranth.  However, few residual herbicides can be applied over-the-top of cotton without the potential for significant injury.  For example, topical applications of Cotoran (fluometuron), Envoke (trifloxysulfuron), and Staple LX (pyrithiobac) have all been reported to cause injury, and in some cases, reduction in yield.  Recently, topical applications of Dual Magnum (s-metolachlor) and Warrant (encapsulated acetochlor) have increased in popularity.  These herbicides have demonstrated the ability to provide adequate preemergence control of GR Palmer amaranth with little to some injury noted.  Typical injury by these herbicides is described as necrotic speckling on exposed leaves and a leathery appearance of developing leaves.  Furthermore, the addition of a tank mix partner, especially Staple LX, was originally thought to increase necrosis caused by Dual Magnum and Warrant on cotton.  However, previous research on this topic is limited.  Therefore, the objectives of our study were to determine if Staple LX enhances injury caused by Dual Magnum/Warrant and also compare Palmer amaranth control by these tank mixes in Roundup- and Liberty-based herbicide programs.