Dilpreet S. Riar

Glyphosate Resistance in a Johnsongrass (Sorghum halepense) Biotype from Arkansas

Abstract Johnsongrass is one of the most troublesome weeds of the world and is listed as a noxious weed in Arkansas. Reduced johnsongrass control with the recommended application rate of glyphosate (840 g ae ha−1) was reported in a continuous soybean field near West Memphis, AR, in the fall of 2007. A greenhouse study was conducted (1) to confirm and characterize glyphosate resistance in the johnsongrass biotype from West Memphis and (2) to determine whether resistant and susceptible biotypes have differential glyphosate absorption or translocation. Dose–response studies revealed that the resistant biotype was five- to seven-fold less sensitive to glyphosate than the susceptible biotype. Glyphosate absorption was similar in resistant and susceptible biotypes at 72 h after treatment (HAT). However, the treated leaf of the resistant biotype retained 28 percentage points more absorbed 14C glyphosate compared to the susceptible biotype at 72 HAT. Additionally, the resistant biotype had less 14C glyphosate translocated to the aboveground tissue below the treated leaf and to roots compared to the susceptible biotype at 24 and 72 HAT. Reduced translocation and increased retention of glyphosate in treated leaves is a probable mechanism of resistance in this glyphosate-resistant johnsongrass biotype. Nomenclature: Glyphosate; johnsongrass, Sorghum halepense (L.) Pers.

Assessment of Weed Management Practices and Problem Weeds in the Midsouth United States—Soybean: A Consultant's Perspective

Abstract Soybean consultants from Arkansas, Louisiana, Mississippi, and Tennessee were surveyed by direct mail and by on-farm visits in fall 2011 to assess weed management practices and the prevalence of weed species in midsouth U.S. soybean. These consultants represented 15, 21, 5, and 10% of total soybean planted in Arkansas, Louisiana, Mississippi, and Tennessee, respectively, in 2011. Collectively, 93% of the total scouted area in these four states was planted with glyphosate-resistant (RR) soybean. The adoption of glufosinate-resistant (LL) soybean was greatest in Arkansas (12%), followed by Tennessee (4%), Mississippi (2%), and Louisiana (< 1%). Only 17% of the RR soybean was treated solely with glyphosate, compared with 35% of LL soybean treated solely with glufosinate. Across four states, average cost of herbicides in RR and LL soybean systems was US

Confirmation, Control, and Physiology of Glyphosate-Resistant Giant Ragweed (Ambrosia trifida) in Arkansas

78 and US

Adoption of Best Management Practices for Herbicide-Resistant Weeds in Midsouthern United States Cotton, Rice, and Soybean

91 ha−1, respectively. Collectively across states, total scouted area under conventional tillage was 42%, stale seedbed was 37%, and no-tillage was 21%. Palmer amaranth and morningglories were the most problematic weeds in all four states. Additionally, barnyardgrass and horseweed were the third most problematic weeds of Arkansas and Tennessee, respectively, and Italian ryegrass was the third most problematic weed in Louisiana and Mississippi. Glyphosate-resistant Palmer amaranth infested fewer fields in Louisiana (16% of fields) than it did in the remaining three states (54% collectively). Average Palmer amaranth hand-weeding costs in the midsouth was US

Inheritance and physiological basis for 2,4-D resistance in prickly lettuce (Lactuca serriola L.).

59 ha−1. Three-fourths of the midsouth consultants stipulated the need for continued research and education focused on management of glyphosate-resistant and glyphosate-tolerant weed species. Nomenclature: Glufosinate; glyphosate; barnyardgrass; Echinochloa crus-galli (L.) Beauv.; horseweed; Conyza canadensis (L.) Cronq.; Italian ryegrass; Lolium perenne L. ssp. multiflorum (Lam.) Husnot; morningglory; Ipomoea spp.; Palmer amaranth; Amaranthus palmeri S. Wats.; soybean; Glycine max (L). Merr. Resumen Asesores en soya de Arkansas, Louisiana, Mississippi, y Tennessee fueron encuestados vía correo y visitas en finca en el otoño de 2011 para evaluar las prácticas de manejo de malezas y la prevalencia de especies de malezas en la producción de soya en el Sur medio de los Estados Unidos. Estos asesores representaron 15, 21, 5 y 10% del total de soya plantada en Arkansas, Louisiana, Mississippi, y Tennessee, respectivamente en 2011. Colectivamente, 93% del total del área evaluada en estos cuatro estados fue sembrada con soya resistente a glyphsoate (RR). La adopción de soya resistente a glufosinate (LL) fue mayor en Arkansas (12%), seguida por Tennessee (4%), Mississippi (2%) y Louisiana (<1%). Solamente 17% de la soya RR fue tratada únicamente con glyphosate, al compararse con 35% de soya LL que fue tratada solamente con glufosinate. En los cuatro estados, el costo promedio de herbicidas en sistemas de soya RR y LL fue US

Consultant Perspectives on Weed Management Needs in Midsouthern United States Cotton: A Follow-Up Survey

78 y US

EST-SSR Development from 5 Lactuca Species and Their Use in Studying Genetic Diversity Among L. serriola Biotypes

91 ha−1, respectivamente. Colectivamente en los estados, el total del área evaluada que estuvo bajo labranza convencional fue 42%, siembra retrasada 37%, y cero labranza 21%. Amaranthus palmeri e Ipomoea spp. fueron las malezas más problemáticas en todos los cuatro estados. Adicionalmente, Echinochloa crus-galli y Conyza canadensis fueron las terceras malezas más problemáticas en Arkansas y Tennessee, respectivamente, y Lolium perenne fue la tercera maleza más problemática en Louisiana y Mississippi. A. palmeri resistente a glyphosate infestó menos campos en Louisiana (16% de los campos) que en el resto de los tres estados (54% colectivamente). El promedio del costo de deshierba manual de A. palmeri en el Sur medio fue de US

Herbicide Programs for Enhanced Glyphosate-Resistant and Glufosinate-Resistant Cotton (Gossypium hirsutum)

59 ha−1. Tres cuartos de los asesores del Sur medio estipularon la necesidad de investigación y educación continuas enfocadas en el manejo de malezas resistentes y tolerantes a glyphosate

Acetolactate Synthase–Inhibiting, Herbicide-Resistant Rice Flatsedge (Cyperus iria): Cross-Resistance and Molecular Mechanism of Resistance

Abstract Glyphosate-resistant giant ragweed in Arkansas was reported in 2005. A study was conducted to (1) confirm and characterize the glyphosate resistance in giant ragweed, (2) determine if reduced absorption or translocation is the mechanism of glyphosate resistance in giant ragweed, and (3) evaluate the efficacy of nine POST-applied soybean herbicides to control glyphosate-resistant and -susceptible giant ragweed. Based on the rate required to kill 50% of plants (LD50 values), resistant giant ragweed biotypes from Greene and Jefferson counties were 2.3- to 7.2-fold less sensitive to glyphosate compared to susceptible biotypes. Glyphosate absorption and translocation for glyphosate-resistant and -susceptible biotypes was similar at 24 and 72 h after treatment. Thus, differential absorption or translocation is not a mechanism of glyphosate resistance in this resistant giant ragweed biotype. Control of resistant giant ragweed biotypes with glyphosate at a labeled field application rate of 840 g ha−1 was only 60% or less compared to complete control of a susceptible giant ragweed biotype. However, bentazon, carfentrazone, cloransulam, and fomesafen controlled both biotypes more than 95%. Nomenclature: Bentazon; carfentrazone; cloransulam; fomesafen; glyphosate; giant ragweed, Ambrosia trifida L.; soybean, Glycine max (L.) Merr.

Use of Imazosulfuron in Herbicide Programs for Drill-Seeded Rice (Oryza sativa) in the Mid-South United States

Abstract In fall 2011, cotton and soybean consultants from Arkansas, Louisiana, Mississippi, and Tennessee were surveyed through direct mail and on-farm visits, and rice consultants from Arkansas and Mississippi were surveyed through direct mail to assess the importance and level of implementation of herbicide resistance best management practices (HR-BMPs) for herbicide-resistant weeds. Proper herbicide timing, clean start with no weeds at planting, application of multiple effective herbicide modes of action, use of full labeled herbicide rates, and prevention of crop weed seed production with importance rating of ≥ 4.6 out of 5.0 were perceived as the most important HR-BMPs in all crops. Purchase of certified rice seed was on 90% of scouted hectares. In contrast, least important HR-BMPs as perceived by consultants with importance ratings of ≤ 4.0 in cotton, ≤ 3.7 in rice, and ≤ 3.8 in soybean were cultural practices such as manual removal of weeds; tillage including disking, cultivation, or deep tillage; narrow (≤ 50 cm)-row crops, cover crops, and altered planting dates. Narrow crop rows and cover crops in cotton; altered planting dates in cotton and soybean; and cleaning of farm equipment and manual weeding in rice and soybean is currently employed on ≤ 20% of scouted hectares. Extra costs, time constraints, adverse weather conditions, lack of labor and equipment, profitability, herbicide-related concerns, and complacency were perceived as key obstacles for adoption of most HR-BMPs. With limited adoption of most cultural practices that reduce risks of herbicide-resistant weeds, there are opportunities to educate growers concerning the proactive need and long-term benefits of adopting HR-BMPs to ensure sustainable weed management and profitable crop production. Nomenclature: Cotton; Gossypium hirsutum L.; rice; Oryza sativa L.; soybean; Glycine max (L.) Merr. Resumen En el otoño de 2011, se encuestó a asesores para la producción de algodón y soya de Arkansas, Louisiana, Mississippi, y Tennessee mediante correo directo o visitas en finca, y a asesores de producción de arroz de Arkansas y Mississippi mediante correo directo, para evaluar la importancia y el nivel de implementación de las mejores prácticas de manejo de resistencia a herbicidas (HR-BMPs) para el manejo de malezas resistentes a herbicidas. El momento apropiado de aplicación del herbicida, la siembra en condiciones libres de malezas, la aplicación de múltiples herbicidas efectivos con diferentes modos de acción, el uso de la dosis alta del herbicida, y la prevención de producción de semilla de malezas dentro del cultivo fueron percibidas como las HR-BMPs más importantes en todos los cultivos con niveles de importancia ≥4.6 de 5.0. La compra de semilla certificada de arroz estuvo presente en 90% de las hectáreas evaluadas. En cambio, las HR-BMPs menos importantes según la percepción de los asesores con niveles de importancia ≤4.0 en algodón, ≤3.7 en arroz, y ≤3.8 en soya fueron prácticas culturales tales como la deshierba manual, la labranza con discos, el cultivo, o la labranza profunda, el uso de distancias de siembra reducidas entre hileras (≤50 cm), uso de coberturas vivas, y modificación de fechas de siembra. El uso de distancias reducidas entre hileras y de coberturas vivas en algodón, la modificación de fechas de siembra en algodón y soya, y la limpieza de equipo agrícola y la deshierba manual en arroz y soya son utilizados actualmente en ≤20% de las hectáreas evaluadas. Costos extra, limitaciones en disponibilidad de tiempo, condiciones climáticas adversas, falta de mano de obra y equipo, rentabilidad, preocupaciones relacionadas a los herbicidas, y la complacencia fueron percibidos como los principales obstáculos para la adopción de la mayoría de las HR-BMPs. La limitada adopción de la mayoría de las prácticas culturales para reducir los riesgos de las malezas resistentes a herbicidas, indican que existen oportunidades para educar a los productores sobre la necesidad y los beneficios en el largo plazo de adoptar HR-BMPs para asegurar el manejo sostenible de malezas y la rentabilidad de la producción.