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Effect of Weed Management on Fruiting Position and Yield of RoundUp Ready Flex Cotton




Haas, John

Type of Degree



Agronomy and Soils


Roundup Ready Flex cotton was commercially available in 2006 and growers need production information about this new technology. Field trials were conducted at the Prattville Experiment Field, Prattville, AL and the Field Crops Unit, Shorter, AL in 2005 to evaluate the influence of 10 weed management systems on fruiting position and yield of Roundup Ready Flex Cotton (Gossypium hirsutum L.). Individual treatments consisted of glyphosate (Roundup Weather Max) at a rate of 1.0 kg ai/ha either alone, with a preemergence herbicide (PRE), or as a tank mix with other postemergence (POST) herbicides. Glyphosate applications were made at weed growth stages of 5 to 7.6 cm, 10 to15.2 cm, and 17.8-22.8 cm for Treatments 1, 2, and 3 respectively. Glyphosate was tank-mixed with acephate (Orthene) and mepiquat chloridide (Pix) for Treatment 4. Treatment 5 consisted of fluometuron (Cotoran) applied PRE followed by (fb) glyphosate + pyrithiobac (Staple) fb glyphosate at a weed heights of 5-7.6 cm. Treatment 6 received fluometuron + pyrithiobac PRE fb glyphosate at 5-7.6 cm tall weeds. Treatment 7 applications included glyphosate fb trifloxysulfuron (Envoke) + nonionic surfactant (NIS) fb glyphosate when weeds reached 5-7.6 cm. Treatment 8 received glyphosate + pyrithiobac fb trifloxysulfuron + NIS fb glyphosate at weed heights of 5-7.6 cm. Applications for treatment 9 included glyphosate + metolachlor (Dual Magnum) fb trifloxysulfuron + NIS at 5-7.6 cm tall weeds. Treatment 10 consisted of pendimethalin (Prowl) PRE fb glyphosate when weed reached a height of 5-7.6 cm. Plots consisted of four rows 7.7 m in length with 91 cm between rows. Treatments were applied in 140 L/ha and replicated four times. Box mapping (fruiting position) was obtained from 3m of the middle right row of each plot. Significant treatment differences for weed control were obtained for grasses (50% Digitaria spp. and 50% Eleusine indica (L.) Gaertn, Ipomoea hederacea var. intergriuscula Gray, and Amaranthus spinosus L. The numerically highest seed cotton yields were obtained with Treatment 6 at FCU (2665 kg ha-1) and Treatment 5 at PEF (2921 kg ha-1). Treatment 3, where glyphosate application was delayed until weeds reached 17.8-22.8 cm in height, had lower yields caused by a reduction in boll number and boll weight at the lower nodes. Some compensation occurred because cotton produced more bolls at higher nodes. The addition of pyrithiobac to glyphosate fb trifloxysulfuron tended to adversely affect yield and fruiting at both trial locations. Fluometuron PRE fb glyphosate did not adversely affect yield or fruiting position.