John Sanders Richburg

The discovery of Arylex™ active and Rinskor™ active: Two novel auxin herbicides.

Multiple classes of commercially important auxin herbicides have been discovered since the 1940s including the aryloxyacetates (2,4-D, MCPA, dichlorprop, mecoprop, triclopyr, and fluroxypyr), the benzoates (dicamba), the quinoline-2-carboxylates (quinclorac and quinmerac), the pyrimidine-4-carboxylates (aminocyclopyrachlor), and the pyridine-2-carboxylates (picloram, clopyralid, and aminopyralid). In the last 10 years, two novel pyridine-2-carboxylate (or picolinate) herbicides were discovered at Dow AgroSciences. This paper will describe the structure activity relationship study that led to the discovery of the 6-aryl-picolinate herbicides Arylex™ active (2005) and Rinskor™ active (2010). While Arylex was developed primarily for use in cereal crops and Rinskor is still in development primarily for use in rice crops, both herbicides will also be utilized in additional crops.

Controlling Glyphosate-Resistant Palmer Amaranth (Amaranthus palmeri) in Cotton with Resistance to Glyphosate, 2,4-D, and Glufosinate

Abstract Field experiments were conducted in Macon County, Georgia, during 2010 and 2011 to determine the impact of new herbicide-resistant cotton and respective herbicide systems on the control of glyphosate-resistant Palmer amaranth. Sequential POST applications of 2,4-D or glufosinate followed by diuron plus MSMA directed at layby (late POST-directed) controlled Palmer amaranth 62 to 79% and 46 to 49% at harvest when the initial application was made to 8- or 18–cm-tall Palmer amaranth, in separate trials, respectively. Mixtures of glufosinate plus 2,4-D applied sequentially followed by the layby controlled Palmer amaranth 95 to 97% regardless of Palmer amaranth height. Mixing glyphosate with 2,4-D improved control beyond that observed with 2,4-D alone, but control was still only 79 to 86% at harvest depending on 2,4-D rate. Sequential applications of glyphosate plus 2,4-D controlled Palmer amaranth 95 to 96% following the use of either pendimethalin or fomesafen. Seed cotton yield was at least 30% higher with 2,4-D plus glufosinate systems compared to systems with either herbicide alone. The addition of pendimethalin and/or fomesafen PRE did not improve Palmer amaranth control or yields when glufosinate plus 2,4-D were applied sequentially followed by the layby. The addition of these residual herbicides improved at harvest control (87 to 96%) when followed by sequential applications of 2,4-D or 2,4-D plus glyphosate; yields from these systems were similar to those with glufosinate plus 2,4-D. Comparison of 2,4-D and 2,4-DB treatments confirmed that 2,4-D is a more effective option for the control of Palmer amaranth. Results from these experiments suggest cotton with resistance to glufosinate, glyphosate, and 2,4-D will improve Palmer amaranth management. At-plant residual herbicides should be recommended for consistent performance of all 2,4-D systems across environments, although cotton with resistance to glyphosate, glufosinate, and 2,4-D will allow greater flexibility in selecting PRE herbicide(s), which should reduce input costs, carryover concerns, and crop injury when compared to current systems. Nomenclature: 2,4-D; 2,4-DB; diuron; glufosinate; glyphosate; MSMA; Palmer amaranth, Amaranthus palmeri (S.) Wats. AMAPA; cotton, Gossypium hirsutum L. Resumen Experimentos de campo fueron realizados en el condado Macon, Georgia, durante 2010 y 2011 para determinar el impacto de nuevos sistemas de algodón resistentes a herbicidas y sus respectivos herbicidas en el control de Amaranthus palmeri resistente a glyphosate. Aplicaciones secuenciales POST de 2,4-D o glufosinate seguidas de diuron más MSMA dirigidas a la base del cultivo (aplicaciones POST dirigidas tarde en el ciclo de crecimiento) controlaron A. palmeri 62 a 79% y 46 a 49% al momento de la cosecha cuando la aplicación inicial se hizo a A. palmeri de 8 a 18 cm de altura, en estudios independientes, respectivamente. Mezclas de glufosinate más 2,4-D aplicados secuencialmente seguidos por la aplicación dirigida controlaron A. palmeri 95 a 97% sin importar la altura de la maleza. El mezclar glyphosate con 2,4-D mejoró el control más allá del control observado con 2,4-D solo, pero aún así el control fue solamente 79 a 86% al momento de la cosecha, dependiendo de la dosis de 2,4-D. Aplicaciones secuenciales de glyphosate más 2,4-D controlaron A. palmeri 95 a 96% cuando se usaron después de aplicaciones de pendimethalin o fomesafen. El rendimiento de semilla del algodón fue al menos 30% mayor en sistemas con 2,4-D más glufosinate en comparación con los sistemas que tuvieron solamente aplicaciones de cualquiera de estos dos herbicidas solos. La adición de pendimethalin y/o fomesafen PRE no mejoró el control de A. palmeri ni los rendimientos cuando se realizaron aplicaciones secuenciales de glufosinate más 2,4-D seguidas por aplicaciones dirigidas. La adición de estos herbicidas residuales mejoró el control al momento de la cosecha (87 a 96%) cuando fueron seguidos de aplicaciones secuenciales de 2,4-D o 2,4-D más glyphosate. Los rendimientos de estos sistemas fueron similares a los de glufosinate más 2,4-D. Comparaciones entre tratamientos de 2,4-D y 2,4-DB confirmaron que 2,4-D es una opción más efectiva para el control de A. palmeri. Los resultados de estos experimentos sugieren que el algodón con resistencia a glufosinate, glyphosate, y 2,4-D mejorará el manejo de A. palmeri. El uso de herbicidas residuales debería ser recomendado para promover un desempeño consistente de todos los sistemas con 2,4-D en diferentes ambientes, aunque el algodón con resistencia a glyphosate, glufosinate, y 2,4-D permitirá una mayor flexibilidad en la selección de herbicidas PRE, lo cual podría reducir el costo en insumos, las preocupaciones por limitaciones en la rotación de cultivos debido a larga residualidad, y el riesgo de daño del cultivo, en comparación con los sistemas actuales.

Effect of Wheat Herbicide Carryover on Double-Crop Cotton and Soybean

Abstract In the southeastern United States many farmers double-crop winter wheat with soybean or cotton. However, there is little information about residual injury of herbicides used in wheat to these rotational crops. Experiments were conducted from 2007 to 2008 and 2008 to 2009 in soft red winter wheat to evaluate response of rotational crops of soybean and cotton after application of various acetolactate synthase herbicides in wheat. Pyroxsulam, mesosulfuron, sulfosulfuron, propoxycarbazone, or chlorsulfuron plus metsulfuron at multiple rates were applied to wheat approximately 110 to 120 d before planting rotational crops. Soils were Tift loamy sand at Ty Ty, GA and Faceville sandy loam at Plains, GA. After wheat harvest, soybean (‘Pioneer 97M50’) and cotton (‘DP 0949 B2RF’) were strip-tillage planted and evaluated for injury, stand density, height over time, and yields. For both locations, wheat was tolerant to all herbicide treatments with little to no visible injury 7 to 90 d after application. Pyroxsulam injury was less than sulfosulfuron or mesosulfuron. At recommended use rates, wheat injury was transient with no effect on yield. Double-crop soybean for both locations had no differences in stand establishment for any herbicide treatments. There was significant carryover injury to soybean and cotton for sulfosulfuron applied to wheat for the Faceville sandy loam. There was no effect of herbicide treatment on cotton stand. There was little to no difference in residual activity on rotational crops between pyroxsulam and other wheat herbicides when labeled rates were applied. This is significant as pyroxsulam is used to control Italian ryegrass and wild radish in this region. Nomenclature: Mesosulfuron; pyroxsulam; propoxycarbazone; sulfosulfuron; cotton, Gossypium hirsutum L.; soybean, Glycine max Merr. (L.), wheat, Triticum aestivum L.

Evaluating the Volatility of Three Formulations of 2,4-D When Applied in the Field

Abstract Cotton genetically engineered to be resistant to topical applications of 2,4-D could provide growers with an additional tool for managing difficult-to-control broadleaf species. However, the successful adoption of this technology will be dependent on the ability of growers to manage off-target herbicide movement. Field experiments were conducted in Moultrie, GA, to evaluate cotton injury resulting from the volatilization of 2,4-D when formulated as an ester, an amine, or a choline salt. Each formulation of 2,4-D (2.24 kg ha−1) was applied in mixture with glyphosate (2.24 kg ha−1) directly to the soil surface (10 to 20% crop residue) in individual square blocks (750 m2). Following herbicide applications, replicate sets of four potted cotton plants (five- to seven-leaf stage) were placed at distances ranging from 1.5 to 48 m from the edge of each treatment. Plants were allowed to remain in-field for up to 48 h before being removed. Cotton exposed to 2,4-D ester for 48 h exhibited maximum injury ratings of 63, 57, 48, 29, 13, and 2% at distances of 1.5, 3, 6, 12, 24, and 48 m, respectively. Less than 5% injury was noted for the amine and choline formulations at any distance. Plant height was also affected by formulation and distance; plants that were located closest to the ester-treated block were smaller than their more distantly-positioned counterparts. Exposure to the amine and choline formulations did not affect plant heights. Additionally, two plastic tunnels were placed inside of each treated block to concentrate volatiles and maximize the potential for crop injury. Injury ratings of 76, 13, and 5% were noted for cotton exposed to the ester, amine, and choline formulations, respectively when under tunnels for 48 h. Results indicate that the choline formulation of 2,4-D was less volatile and injurious to cotton than the ester under the field conditions in this study. Nomenclature: 2,4-dichlorophenoxyacetic acid, glyphosate; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; cotton, Gossypium hirsutum L. Resumen El algodón genéticamente diseñado para ser resistente a las aplicaciones tópicas de 2,4-D podría brindar a los productores una herramienta adicional para el manejo de especies de hoja ancha difíciles de controlar. Sin embargo, la adopción exitosa de esta tecnología dependerá de la habilidad de los productores de manejar el movimiento del herbicida a lugares no deseados. Se realizaron experimentos de campo en Moultrie, Georgia, para evaluar el daño en algodón resultante de la volatilización de 2,4-D cuando se formuló como ester, amine, o sal choline. Cada formulación de 2,4-D (2.24 kg ha−1) fue aplicada en mezcla con glyphosate (2.24 kg ha−1) directamente a la superficie del suelo (10 a 20% de residuos de cultivos) en parcelas cuadradas individuales (750 m2). Seguido de las aplicaciones del herbicida, grupos replicados de cuatro plantas de algodón en contenedores (en el estado de cinco a siete hojas) fueron colocados a distancias que variarían de 1.5 a 48 m del borde de cada tratamiento. Las plantas fueron mantenidas en el campo por períodos de hasta 48 h antes de ser removidas. El algodón expuesto a 2,4-D ester por 48 h mostró evaluaciones de daño máximas de 63, 57, 48, 29, 13, y 2% a distancias de 1.5, 3, 6, 12, 24, y 48 m, respectivamente. Para las formulaciones amine y choline, el daño notado fue menor a 5% en cualquiera de las distancias evaluadas. La altura de planta también fue afectada por la formulación y la distancia; las plantas que estaban más cerca de la parcela tratada con ester fueron más pequeñas que aquellas que estaban a mayor distancia. La exposición a las formulaciones amine y choline no afectó la altura de las plantas. Adicionalmente, se colocaron dos túneles de plástico dentro de cada parcela tratada para concentrar los compuestos volátiles y maximizar el potencial de daño del cultivo. Las evaluaciones de daño de 76, 13, y 5% fueron notadas para el algodón expuesto a las formulaciones ester, amine, y choline, respectivamente, bajo los túneles por 48 h. Los resultados indican que la formulación choline de 2,4-D fue menos volátil y menos dañina al algodón que la formulación ester bajo condiciones de campo en este estudio.

Salvage Palmer Amaranth Programs Can Be Effective in Cotton Resistant to Glyphosate, 2,4-D, and Glufosinate

Abstract Glyphosate-resistant Palmer amaranth escaping residual herbicides is difficult to manage in cotton because of its rapid growth and a limited number of effective herbicide options to control emerged plants. An experiment was conducted at two dryland and two irrigated sites in Georgia during 2011 and 2012 to determine if cotton resistant to glyphosate, 2,4-D, and glufosinate could be used to salvage a crop infested with large Palmer amaranth. Three POST herbicide systems, including sequential applications of 2,4-D, sequential applications of 2,4-D plus glufosinate, or 2,4-D followed by (fb) glufosinate, were applied with intervals of 5, 10, or 15 d between POST applications. All three systems were followed by diuron plus MSMA directed at layby. At the dryland sites with high temperatures and drought conditions, no program provided greater than 90% control. However, the 2,4-D plus glufosinate system was at least twice as effective in controlling 20-cm-tall Palmer amaranth and produced at least three times more cotton than the other two systems, when pooled over POST application intervals. Intervals of 10 or 15 d between POST applications were 23 to 27% more effective than a 5-d interval in controlling Palmer amaranth when pooled over POST herbicide systems; yields were nearly twice as much with the 10-d interval compared to 5 d. At the irrigated site, overall weed control was greater with less treatment differences noted. Palmer amaranth that was 20 cm tall at application was controlled 98 to 99%, 92 to 93%, and 81 to 94% by glufosinate plus 2,4-D, 2,4-D fb glufosinate, and 2,4-D fb 2,4-D systems at harvest, respectively. Intervals between POST applications only influenced control by the POST 2,4-D system, and the 10-d interval was more effective than the 5-d interval. Carpetweed, Florida beggarweed, and smallflower morningglory were controlled 99% at harvest by all systems; however, it was noted that control of carpetweed and Florida beggarweed prior to layby was less effective with 2,4-D than systems including glufosinate. In the event of an at-plant residual herbicide failure in fields infested with glyphosate-resistant Palmer amaranth, our research demonstrates that glufosinate plus 2,4-D sequentially applied 10 to 15 d apart followed by a timely layby application controlled the target weeds in cotton with resistance to 2,4-D, glyphosate, and glufosinate. Nomenclature: 2,4-D; diuron; glufosinate; glyphosate; MSMA; carpetweed, Mollugo verticillata L. MOLVE; Florida beggarweed, Desmodium tortuosum [Sw] DC. DEDTO; Palmer amaranth, Amaranthus palmeri (S.) Wats. AMAPA; smallflower morningglory, Jacquemontia tamnifolia [L.] Griseb. IAQTA; cotton, Gossypium hirsutum L. Resumen En algodón y cuando escapa a herbicidas residuales, Amaranthus palmeri resistente a glyphosate es difícil de manejar debido a su rápido crecimiento y al limitado número de opciones de herbicidas efectivos para el control de plantas emergidas. Se realizó un experimento en dos sitios sin riego y en dos sitios con riego en Georgia en 2011 y 2012 para determinar si el algodón resistente a glyphosate, 2,4-D, y glufosinate podría ser usado para salvar a un cultivo infestado con plantas grandes de A. palmeri. Tres sistemas de herbicidas POST, los cuales incluyeron aplicaciones secuenciales de 2,4-D, aplicaciones secuenciales de 2,4-D más glufosinate, o 2,4-D seguido de (fb) glufosinate, fueron aplicados a intervalos de 5, 10 ó 15 d entre aplicaciones POST. Los tres sistemas fueron seguidos por diuron más MSMA dirigido antes del cierre del dosel. En los sitios sin riego, con altas temperaturas y condiciones de sequía, ningún programa brindó control superior a 90%. Sin embargo, el sistema de 2,4-D más glufosinate fue al menos el doble de efectivo controlando A. palmeri de 20 cm de altura y produjo al menos tres veces más algodón que los otros dos sistemas, cuando se promediaron los intervalos de aplicación POST. Los intervalos de 10 ó 15 d entre aplicaciones POST fueron 23 a 27% más efectivos que el intervalo de 5 d para el control de A. palmeri cuando se promediaron los sistemas de herbicidas POST. El rendimiento con el intervalo de 10 d fue casi el doble al compararse con el intervalo de 5 d. En el sitio con riego, el control de malezas fue en general mayor y se notaron menos diferencias entre tratamientos. A. palmeri que tenía 20 cm de altura al momento de aplicación fue controlado 98 a 99%, 92 a 93%, y 81 a 94% con los sistemas glufosinate más 2,4-D, 2,4-D fb glufosinate, y 2,4-D fb 2,4-D, respectivamente al momento de la cosecha. Los intervalos entre aplicaciones POST solamente influenciaron el control de los sistemas POST con 2,4-D, y el intervalo de 10 d fue más efectivo que el de 5 d. Mollugo verticillata, Desmodium tortuosum, y Jacquemontia tamnifolia fueron controlados 99% al momento de la cosecha en todos los sistemas. Sin embargo, se notó que el control de M. verticillata y D. tortuosum antes del cierre del dosel fue menos efectivo con 2,4-D que los sistemas que incluyeron glufosinate. En la eventualidad de una falla en el control residual al momento de la siembra, en campos infestados con A. palmeri resistente a glyphosate, nuestra investigación demuestra que glufosinate más 2,4-D aplicados secuencialmente 10 a 15 d aparte seguidos por una aplicación antes del cierre del dosel controló las malezas deseadas en algodón con resistencia a 2,4-D, glyphosate, y glufosinate.

Resistance of Enlist™ (AAD-12) Cotton to Glufosinate

Enlist™ cotton contains the aad-12 and pat genes that confer resistance to 2,4-D and glufosinate, respectively. Thirty-three field trials were conducted focused on Enlist cotton injury from glufosinate as affected by cotton growth stage, application rate, and single or sequential applications. Maximum injury from a single application of typical 1X (542 g ae ha-1) and 2X use rates was 3 and 13%, respectively, regardless of growth stage. Injury from sequential applications of 1X or 2X rates was equivalent to single applications. Similar injury was observed with four commercial formulations of glufosinate. Cotton yield was never affected by glufosinate. This research demonstrates Enlist™ cotton has robust resistance to glufosinate at rates at least twice the typical use rate when applied once or twice at growth stages ranging from 2 to 12 leaves. Nomenclature: Glufosinate; 2,4-D; cotton, Gossypium hirsutum L.