Differential susceptibility of Conyza bonariensis biotypes to glyphosate and ALS-Inhibiting herbicides in Argentina

The aim of this study was to compare control of three stages biotypes (rosette, bolting, and repro- ductive stage) of Conyza bonariensis glyphosate susceptible biotype (S) and tolerant biotype (T) to glyphosate with glyphosate and mixtures of acetolactate synthase (ALS)-inhibiting. For glyphosate, the dose-response curves confirmed that injury of the biotype T relative to biotype S was signifi- cantly lower for both rosette and bolting stages. Resistance index (RI) for this herbicide was approximately 4 for both weed stages. At bolting, for both biotypes doses much higher than the recommended dose were required. For acetolactate synthase (ALS)-inhibiting herbicides, at the rosette stage, control of both biotypes was excellent with doses significantly lower than the recommended rate. All herbicides within this group showed a very low I50 relative to the recommended rate. These results indicate that biotypes difficult to control with glyphosate at the rosette and bolting stage may be controlled using acetolacte synthase (ALS)-inhibiting herbicides. Control for the reproductive stage was poor. A management program based on the combination of glyphosate with pre- and post-emergence acetolactate synthase (ALS) herbicides may be effective to control the weed.EEA ParanáFil: Puricelli, Eduardo Carlos Jose Maria. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; ArgentinaFil: Faccini, Delma Edith. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; ArgentinaFil: Metzler, Marcelo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Paraná; ArgentinaFil: Torres, Patricia Susana. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; Argentin

Sensitivity of conyza sumatrensis biotypes to glyphosate and ALS-inhibiting herbicides at two growth stages

Conyza sumatrensis es una de las malezas más problemáticas de Argentina, con frecuentes fallas de control después de la aplicación de glifosato. El objetivo del trabajo fue evaluar la sensibilidad de biotipos de C. sumatrensis, en dos estados de desarrollo (roseta y vegetativo), a glifosato y a inhibidores de la enzima acetolactato sintasa (ALS). Se realizaron estudios de dosis-respuesta utilizando 0, 1/16, 1/8, 1/4, 1/2, 1, 2, 4, 8 y 16 veces la dosis recomendada para cada herbicida. Al estado de roseta el nivel de resistencia para glifosato fue de 9,8, mientras que en estado vegetativo ninguno de los biotipos fue controlado con la dosis recomendada, siendo menor la sensibilidad del biotipo R (IR = 2,3). El control de ambos biotipos con inhibidores de la ALS fue excelente al estado de roseta, con dosis menores que las recomendadas. Al estado vegetativo los controles fueron adecuados (80 %) con dosis menores que las recomendadas (0,16 X a 0,97 X), excepto para metsulfuron-metil + clorsulfuron en el biotipo S (1,75 X). Estos resultados confirmarían la existencia de un biotipo resistente a glifosato en Argentina y que los herbicidas inhibidores de la ALS pueden controlar biotipos resistentes e individuos más desarrollados.Conyza sumatrensis is one of the most problematic weeds in Argentina, with frequent control failures after glyphosate application. The objective of this research was to evaluate sensitivity of C. sumatrensis biotypes, at two growth stages (rosette and vegetative), to glyphosate and acetolactate synthase (ALS)-inhibiting herbicides. Dose-response experiments were performed using 0, 1/16, 1/8, 1/4, 1/2, 1, 2, 4, 8, and 16-fold of the recommended dose for each herbicide. At rosette stage, the resistance level for glyphosate was 9.8, while at the vegetative stage neither biotype was controlled with the recommended dose, with lower sensitivity of biotype R (RI = 2.3). Control of both biotypes using ALS-inhibiting herbicides was excellent at rosette stage, with lower doses than the recommended. At vegetative stage controls were good (80 %) with lower doses than recommended (0.16 X to 0.97 X), except for metsulfuron-methyl + chlorsulfuron in biotype S (1.75 X). These results may confirm the existence of a biotype resistant to glyphosate in Argentina and that ALS-inhibiting herbicides could control resistant biotypes and more developed individuals.Fil: Balassone, Federico Emmanuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; ArgentinaFil: Puricelli, Eduardo Carlos Jose Maria. Universidad Nacional de Rosario. Facultad de Cs.agrarias. Departamento de Producción Vegetal. Cátedra Terapeutica Vegetal; ArgentinaFil: Faccini, Delma Edith. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; Argentin

Anoda cristata control with glyphosate in narrow- and wide-row soyabean

Experiments evaluated the effect of glyphosate rate and Anoda cristata density, on crop and weed biomass and weed seed production in wide (70 cm) and narrow rows (35 cm) glyphosate-resistant soyabean (Glycine max). Soyabean density was higher at 35 cm row spacing as an increase in planting rate in narrow-row soyabean is recommended for producers in Argentina. Soyabean biomass at growth stage V4 (four nodes on the main stem with fully developed leaves beginning with the unifoliate leaves) was higher when grown on narrow than in wide-rows but was not affected by the presence of A. cristata. At growth stage R5 (seed initiation – seed 3 mm long in a pod at one of the four uppermost nodes on the main stem, with a fully developed leaf and full canopy development), crop biomass was greater in narrow rows compared with wide rows with 12 plants m−2 of A. cristata. In narrow-row soyabean, a single application of a reduced rate of glyphosate maintained soyabean biomass at R5 and provided excellent weed control regardless of weed density. In wide-row soyabean control was reduced at the high weed density. Regardless of row spacing, A. cristata biomass and seed production were severely reduced by half of the recommended dose rate of glyphosate but the relationship between biomass and seed production was not altered. Glyphosate rates as low as 67.5 g a.e. ha−1 in narrow rows or 540 g a.e. ha−1 in wide rows provided excellent control of A. cristata. To minimize glyphosate use, planting narrow-row soyabean are effective where A. cristata density is low.Fil: Puricelli, Eduardo Carlos Jose Maria. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; ArgentinaFil: Faccini, Delma Edith. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; ArgentinaFil: Orioli, Gustavo Adolfo. Universidad Nacional del Sur. Departamento de Agronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; ArgentinaFil: Sabbatini, Mario Ricardo. Universidad Nacional del Sur. Departamento de Agronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentin