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There has been renewed interest in using fluridone herbicide to aid in control of glyphosateresistant Palmer amaranth (Amaranthus palmeri S. Watson) in cotton (Gossypium hirsutum L.). Section 18 Emergency Use Exemptions for fluridone in cotton have been granted recently in several states and the manufacturer is pursuing federal registration. Fluridone has long persistence in soil, leading to questions about rotational crop response. Field experiments were conducted in North Carolina to evaluate the potential for fluridone to carry over to corn (Zea mays L.), peanut (Arachis hypogaea L.), grain sorghum [Sorghum bicolor (L.) Moench.], and soybean [Glycine max (L.) Merr.] grown in rotation with fluridone-treated cotton. Fluridone at 0, 280, 420, 560, 840, and 1120 g ai ha-1 was applied preemergence to cotton and rotational crops were planted the following spring. The fluridone rates were well above proposed use rates. Only minor visible injury to cotton was observed and cotton yield was unaffected by fluridone. Fluridone also caused only minor visible injury to rotational crops and did not affect stands, early season height, or yield of rotational crops. [ABSTRACT FROM AUTHOR]

Recommendations to control glyphosateresistant Palmer amaranth (Amaranthus palmeri S. Wats.) in cotton (Gossypium hirsutum L.) typically include glufosinate applied postemergence (POST) and residual herbicides applied both preemergence and POST. Residual herbicide options for POST application are limited primarily to pyrithiobac and the chloroacetamides herbicides acetochlor and S-metolachlor. Labeling for pyrithiobac warns of injury when mixed with metolachlor. No published information is available on crop or weed response to mixtures of glufosinate plus acetochlor, with or without pyrithiobac. Tolerance of WideStrike® cotton and Palmer amaranth control with glufosinate applied alone to 1- to 2-leaf cotton, glufosinate mixed with pyrithiobac or micro-encapsulated acetochlor or S-metolachlor, and three-way combinations of glufosinate plus acetochlor or S-metolachlor plus pyrithiobac were evaluated in field experiments. These treatments were followed by a second application of glufosinate and diuron plus MSMA directed at layby. Prior to the second application, glufosinate early POST alone controlled Palmer amaranth 77%. Pyrithiobac mixed with glufosinate increased control 10 to 11%, whereas acetochlor and S-metolachlor increased control 12 to 14%. Control was similar with glufosinate plus acetochlor with or without pyrithiobac, whereas combinations of glufosinate plus S-metolachlor plus pyrithiobac were 4 to 5% more effective than glufosinate plus S-metolachlor. Pyrithiobac increased cotton necrosis 3 to 4% and reduced growth 5% 7 d after application compared to glufosinate alone. Acetochlor and S-metolachlor increased necrosis 14 to 18% and reduced growth 7 to 10%. Necrosis was similar with glufosinate plus acetochlor with or without pyrithiobac. Pyrithiobac added to glufosinate plus S-metolachlor increased necrosis 3 to 4%. Injury was transient, and no differences in lint yield were noted among herbicide treatments. [ABSTRACT FROM AUTHOR]

Glufosinate controls GR Palmer amaranth (Amaranthus palmeri S. Wats.), but might be less effective than glyphosate on certain weeds. Glyphosate and glufosinate applications in tolerant cotton (Gossypium hirsutum L.) cultivars can broaden the spectrum of control and aid in resistance management. Research investigating sequential application and potential interactions with co-applications of glyphosate and glufosinate is limited. Field research at six locations evaluated Palmer amaranth and annual grass control with glyphosate and glufosinate co-applied or sequentially applied. Herbicides were applied to two-leaf cotton and repeated 14 d later. A GR biotype comprised 10 to 90% of the Palmer amaranth populations. Greater Palmer amaranth control was achieved following sequential applications of glufosinate compared with glyphosate. Co-application of glufosinate plus glyphosate was more effective than glyphosate alone at most locations but never more effective than glufosinate alone. Glyphosate controlled goosegrass (Eleusine indica [L.] Gaertn.) more than glufosinate and a similar response was observed for large crabgrass (Digitaria sanguinalis [L.] Scop.). Glufosinate and glyphosate co-applied were less effective than glyphosate alone on both grasses, but not more effective than glufosinate alone. Glufosinate followed by (fb) glyphosate was the preferred order for sequential application to control Palmer amaranth at most locations. With high percentages of the GR biotype, glufosinate applied sequentially was more effective than any other sequential applications. Glyphosate fb glufosinate and glufosinate fb glyphosate controlled large crabgrass similar to glyphosate applied sequentially and greater than glufosinate applied sequentially. For goosegrass, glyphosate fb glufosinate was more effective than the reverse. Seven days after the second postemergence application, sequential application of glyphosate fb glufosinate controlled goosegrass as well as glyphosate applied sequentially and better than glufosinate applied sequentially. [ABSTRACT FROM AUTHOR]

Glyphosate-resistant Palmer amaranth (Amaranthus palmeri S. Wats.) is a widespread problem in cotton (Gossypium hirsutum L.) production. Growers are encouraged to include residual herbicides applied preemergence (PRE) and postemergence (POST) in their management systems to control this weed adequately. Pyroxasulfone, an isoxazoline herbicide with the same mode of action as acetochlor and S-metolachlor, effectively controls Palmer amaranth in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. The objective of this study was to compare cotton tolerance and Palmer amaranth control with pyroxasulfone, acetochlor, and S-metolachlor applied PRE and POST to cotton. Treatments in a field study at four locations included pyroxasulfone at 60, 90, and 120 g a.i. ha-1 applied PRE or mixed with glyphosate and applied POST; an encapsulated formulation of acetochlor at 1260 g a.i. ha-1 applied PRE or POST with glyphosate; and S-metolachlor at 1070 g a.i. ha-1 applied POST with glyphosate. Pyroxasulfone PRE increased late-season Palmer amaranth control 14 to 27% and increased yield in one of two years. Similar results were observed with pyroxasulfone and acetochlor applied PRE. Pyroxasulfone, acetochlor, and S-metolachlor applied POST with glyphosate did not increase Palmer amaranth control compared with glyphosate alone. Cotton was less tolerant of pyroxasulfone applied PRE or POST than acetochlor applied PRE or POST or S-metolachlor applied POST. Cotton growth was reduced 14 to 17% by pyroxasulfone applied PRE and stand was reduced 10 to 25%. Acetochlor PRE reduced cotton growth 6% but did not affect stand. Pyroxasulfone applied POST caused 23 to 36% necrosis 7 d after application and reduced cotton growth 21 to 39% at 14 d after application compared with 6 to 17% necrosis and 3 to 8% growth reduction caused by acetochlor and S-metolachlor. Yields were not reduced by any treatment. [ABSTRACT FROM AUTHOR]