C. Dale Monks

Weed Management Programs for Glyphosate-Tolerant Cotton (Gossypium hirsutum)1

Abstract: Several herbicide-based weed management programs for glyphosate-tolerant cotton were compared in eight field studies across Alabama during 1996 and 1997. Weed management programs ranged from traditional, soil-applied residual herbicide programs to more recently developed total postemergence (POST) herbicide programs. Pitted morningglory and sicklepod control was best achieved with fluometuron applied preemergence (PRE) followed by (fb) a single POST over-the-top (POT) application of glyphosate fb a POST-directed application of glyphosate. Annual grass control was better with the preplant incorporated (PPI) programs at two of three locations in both years. Treatments that included at least one glyphosate POT application gave increased grass control over no glyphosate or pyrithiobac POT. Velvetleaf control was improved with the addition of glyphosate POT. A herbicide program using no POST herbicides yielded significantly less seed cotton than any program using POST herbicides at one location. PRE- and POST-only weed management programs at another location produced more seed cotton and gave greater net returns than PPI programs. Similarly, net returns at that same location were equivalent for both PRE- and POST-only programs, and less for PPI programs. POST-only programs yielded highest amounts of seed cotton and netted greater returns. Nomenclature: Fluometuron; glyphosate; pyrithiobac; cotton, Gossypium hirsutum L. ‘Deltapine 5415RR’, ‘Deltapine 5690RR’; pitted morningglory, Ipomoea lacunosa L. #3 IPOLA; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB; velvetleaf, Abutilon theophrasti Medik. # ABUTH. Additional index words: Cotton yields, herbicide costs, herbicide-resistant crops, transgenic cotton. Abbreviations: ANOVA, analysis of variance; EPDS, early postemergence-directed spray; EPOT, early postemergence over-the-top; fb, followed by; GCS, Gulf Coast Research and Education Center; LPDS, late postemergence-directed spray; LPOT, late postemergence over-the-top; LSD, least significant difference; PDS, postemergence-directed spray; PEF, Prattville Experimental Field; POST, postemergence; POT, postemergence over-the-top; PPI, preplant incorporated; PRE, preemergence; TVS, Tennessee Valley Research and Education Center; WGS, Wiregrass Research and Education Center.

Glyphosate-Resistant Cotton Response to Glyphosate Applied in Irrigated and Nonirrigated Conditions

Field experiments were conducted in Alabama during 1999 and 2000 to test the hypothesis that any glyphosate-induced yield suppression in glyphosate-resistant cotton would be less with irrigation than without irrigation. Yield compensation was monitored by observing alterations in plant growth and fruiting patterns. Glyphosate treatments included a nontreated control, 1.12 kg ai/ha applied POST at the 4-leaf stage, 1.12 kg/ha applied DIR at the prebloom stage, and 1.12 kg/ha applied POST at 4-leaf and postemergence directed (DIR) at the prebloom cotton stages. The second variable, irrigation treatment, was established by irrigating plots individually with overhead sprinklers or maintaining them under dryland, nonirrigated conditions. Cotton yield and all measured parameters including lint quality were positively affected by irrigation. Irrigation increased yield 52% compared to nonirrigated cotton. Yield and fiber quality effects were independent of glyphosate treatments. Neither yield nor any of the measured variables that reflected whole plant response were influenced by glyphosate treatment or by a glyphosate by irrigation interaction. Nomenclature: Glyphosate; cotton, Gossypium hirsutum L; ‘Delta and Pine Land 458 BGRR’.

Cotton and Weed Response to Glyphosate Applied with Sulfur-Containing Additives1

Field studies were conducted to assess two sulfur-containing additives for use with glyphosate applied postemergence to glyphosate-resistant cotton for the control of sicklepod and yellow nutsedge. Neither diammonium sulfate (AMS) nor ammonium thiosulfate (ATS), both applied at 2.24 kg/ha, increased control of either species. Effective control of both species was dependent on glyphosate (isopropylamine salt) rate alone, with optimum control at 1.26 kg ae/ha. Plant-mapping data further indicated that sulfur-containing additives generally had no effect on either cotton fruiting patterns or yield. However, applying glyphosate at any rate did increase seed cotton yield in 2 of 3 yr vs. no glyphosate. In addition, applying glyphosate at any rate resulted in an increase in the number of bolls vs. no glyphosate in the following plant-mapping responses: total number of bolls per plant, number of abcised bolls per plant, bolls at the top five sympodial nodes, and bolls at positions 1 and 2 on the sympodia. Glyphosate absorption and subsequent translocation, as influenced by the addition of the sulfur-containing additives, was evaluated using radiotracer techniques. Glyphosate absorption after 48 h was 86, 63, and 37% of amount applied in cotton, sicklepod, and yellow nutsedge, respectively. Absorption by sicklepod and yellow nutsedge was not affected by the addition of either of the additives. Absorption by cotton was reduced by ATS but was not affected by AMS. In yellow nutsedge and cotton, glyphosate concentration in the treated area and adjacent tissue was not affected by either additive. A greater portion of glyphosate was translocated away from the treated area in sicklepod with glyphosate plus AMS (32%) than with glyphosate plus ATS (21%). AMS and ATS may be used in glyphosate-resistant cotton without the risk of either crop injury or yield reduction. However, their use for increased control of annual weed species, such as sicklepod and yellow nutsedge, may not be warranted. Nomenclature: Glyphosate; ammonium thiosulfate; diammonium sulfate; sicklepod, Senna obtusifolia (L.) Irwin & Barneby #3 CASOB; yellow nutsedge, Cyperus esculentus L. # CYPES; cotton, Gossypium hirsutum L. ‘Paymaster 1218 BR’. Additional index words: Ammonium thiosulfate, CASOB, CYPES, diammonium sulfate, glyphosate absorption, glyphosate additives, glyphosate-resistant cotton. Abbreviations: AMS, diammonium sulfate; ATS, ammonium thiosulfate; DAT, days after treatment.

Evaluation of Tillage and Herbicide Interaction for Amaranthus Control in Cotton

Abstract Amaranthus control in cotton can be difficult with the loss of glyphosate efficacy, especially in conservation-tillage cropping systems. Research was conduction from 2006 to 2008 at EV Smith Research Center, Shorter, AL, to determine the level of glyphosate-susceptible Amaranthus control provided by four initial tillage and herbicide treatments, including 1) moldboard plowing followed by a single-pass disking and field cultivation plus pendimethalin at 1.2 kg ai ha−1 preplant incorporation (PPI), 2) two-pass disking followed by field cultivation plus pendimethalin at 1.2 kg ha−1 PPI, 3) no tillage including an application of pendimethalin at 1.2 kg ha−1 PRE, or 4) no tillage without pendimethalin in 2006. No further tillage practices or pendimethalin applications were utilized after study initiation. Initial tillage operations, including inversion with disking or disking twice, resulted in Amaranthus density of ≤ 4 plants m−2 and 47 to 82% control, whereas no-tillage treatments had ≥ 4 plants m−2 and 14 to 62% control. Subsequent applications of PRE herbicides included fluometuron at 1.68 kg ai ha−1 or prometryn at 1.12 kg ai ha−1 and provided 53 to 98% and 55 to 93% control, respectively, and reduced Amaranthus density compared to no PRE herbicide to < 2 plants m−2, regardless of tillage treatment. A POST application of glyphosate at 1.0 kg ae ha−1 improved control in conjunction with almost all treatments in each year. Results indicate that a one-time tillage operation followed by a return to reduced tillage may aid in the reduction of Amaranthus density when used with PRE-applied herbicides; however, this system will likely not provide adequate control when high population densities of glyphosate-resistant Amaranthus are present, thus highlighting the need for a highly efficacious POST herbicide system. Resumen El control de Amaranthus en algodón puede ser difícil con la pérdida de eficacia de glyphosate, especialmente en sistemas de cultivos con labranza de conservación. Se realizaron investigaciones desde 2006 a 2008 en el Centro de Investigación EV Smith, en Shorter, Alabama, para determinar el nivel de control de Amaranthus susceptible a glyphosate provisto por cuatro tratamientos con labranza inicial y herbicidas, los cuales incluyeron 1) labranza con arado de vertedera seguida por un único pase de rastra de discos y un cultivador más pendimethalin a 1.2 kg ai ha−2 en pre-siembra incorporado (PPI), 2) dos pases de rastra de discos seguidos por un pase con cultivador más pendimethalin a 1.2 kg ha−1 PPI, 3) sin labranza incluyendo una aplicación de pendimethalin a 1.2 kg ha−1 PRE, o 4) sin labranza y sin pendimethalin en 2006. No se realizaron prácticas adicionales de labranza o aplicaciones de herbicidas después del inicio del estudio. Las operaciones de labranza iniciales que incluyeron inversión del suelo con el pase de discos una o dos veces resultaron en densidades de Amaranthus ≤4 plantas m−2 y 47 a 82% de control, mientras que los tratamientos sin labranza tuvieron ≥4 plantas m−2 y 14 a 62% de control. Las aplicaciones posteriores de herbicidas PRE incluyeron fluometuron a 1.68 kg ai ha−1 o prometryn a 1.12 kg ai ha−1 y brindaron 53 a 98% de control, respectivamente, y redujeron la densidad de Amaranthus en comparación con los tratamientos sin herbicidas PRE a <2 plantas m−2 sin importar el tratamiento de labranza. Una aplicación de glyphosate a 1.0 kg ae ha−1 mejoraron el control en combinación con casi todos los tratamientos en cada año. Los resultados indican que una operación de labranza seguida por labranza reducida podría ayudar en la reducción de la densidad de Amaranthus cuando se usó herbicidas aplicados PRE. Sin embargo, este sistema probablemente no brindará control adecuado cuando altas poblaciones de Amaranthus resistente a glyphosate están presentes, resaltando la necesidad de tener un sistema de herbicidas POST eficaz.

Effectiveness of Ammonium Thiosulfate to Enhance Weed Control and Reduce Cotton (Gossypium hirsutum) Injury1

Abstract: Field experiments were conducted in 1997 and 1998 at the Prattville Experiment Field in Prattville, AL and the Wiregrass Substation in Headland, AL to determine if ammonium thiosulfate (ATS) additions to monosodium methanearsonate (MSMA) affects weed control, reduces MSMA-induced cotton injury, lessens the fruiting and maturity delay on cotton caused by MSMA, and lessens MSMA-induced yield reductions in cotton. Treatments were applied before cotton was at the pinhead square stage and the weeds were 5 cm tall. Weeds evaluated were sicklepod, morningglory species, yellow nutsedge, and Texas panicum. ATS additions to MSMA occasionally enhanced control of all weeds 5 to 20%. However, the addition of ATS did not reduce crop injury caused by MSMA, the effects of MSMA on cotton maturity, or yield reductions caused by MSMA. Nomenclature: MSMA, monosodium methanearsonate; morningglory species, Ipomoea spp. #3 IPOZZ; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB; Texas panicum, Panicum texanum Buckl. # PANTE; yellow nutsedge, Cyperus esculentus L. # CYPES; cotton, Gossypium hirsutum L. Abbreviations: ATS, ammonium thiosulfate; DAT, days after treatment; POST, postemergence.