Master of Science (MS)


Plant, Environmental Management and Soil Sciences

Document Type



Field trials conducted over two years evaluated weed control programs in second generation glyphosate-resistant (GR) cotton (Gossypium hirsutum L.). In a co-application study, glyphosate applied alone at the standard rate or in combination with acephate, acetamiprid, bifenthrin, cyfluthrin, cypermethrin, dicrotophos, dimethoate, emanectin benzoate, imidacloprid, indoxacarb, lambda-cyhalothrin, methoxyfenozide, spinosad, thiamethoxam, zeta-cypermethrin, mepiquat pentaborate, sodium calcium borate, and a foliar nitrogen fertilizer resulted in similar control of barnyardgrass [Echinochloa crus-galli (L.) Beauv.] (96-97%), johnsongrass [Sorghum halepense (L.) Pers.] (98%), hemp sesbania [Sesbania herbacea (P. Mill.) McVaugh] (66-73%), pitted morningglory (Ipomoea lacunosa L.) (67-72%), and sicklepod [Senna obtusifolia (L.) H. S. Irwin & Barneby] (86-91%), regardless of application timings at 3 to 4 lf or 7 to 8 lf weed stages. Additionally, fresh weight reduction was equivalent for treatments of glyphosate alone and co-applications and ranged from 89 to 100%. Weed control data from field studies in second generation GR cotton indicate the inclusion of fluometuron preemergence (PRE) to glyphosate postemergence over-the-top (POT) programs beneficial for some, but not all species evaluated, and very little difference was observed between two or three POT applications of glyphosate. Use of fluometuron PRE can prove beneficial in maximizing yield when early season glyphosate applications are delayed. In a related study, data suggests herbicides s-metolachlor, pyrithiobac, and trifloxysulfuron provide similar season-long control of most weeds evaluated. Barnyardgrass and browntop millet [Urochloa ramosa (L.) Nguyen] control can be maximized with co-application of s-metolachlor and glyphosate. Timing of residual herbicide applied at 2, 6, or 10 lf had little or no affect on control observed. For palmer amaranth (Amaranthus palmeri S. Wats.), sicklepod, barnyardgrass, and browntop millet, season-long control was optimized with residual herbicide applied at the 2 or 10 lf growth stages. Similar yield response can be expected among herbicides evaluated in combination with glyphosate. Analysis of yield data suggest the most consistent residual herbicide application timing for optimizing yield occurred at the 2 lf growth stage.



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Committee Chair

Donnie K. Miller