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1 January 2014 Annual Bluegrass ( Poa annua) Control in Glyphosate-Resistant Perennial Ryegrass Overseeding
Michael L. Flessner, J. Scott McElroy, Glenn R. Wehtje
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‘Replay' and ‘JS501’ perennial ryegrass cultivars have been conventionally bred for reduced sensitivity to glyphosate, potentially allowing the herbicide to be used for selective weed control in overseeded bermudagrass. Field experiments were conducted to evaluate optimal glyphosate application rate, regime (single and sequential applications), and timing for annual bluegrass control in bermudagrass overseeded with these cultivars. Additionally, greenhouse experiments were conducted to compare the sensitivity to glyphosate of Replay and JS501 to susceptible cultivars ‘Caddy Shack' and ‘Top Gun II' through log-logistic rate-response analysis. In field experiments, only two treatments resulted in > 90% annual bluegrass control and < 25% perennial ryegrass injury. These two treatments were a single application of 280 g ae ha−1 glyphosate in January and 140 g ha−1 followed by an additional 140 g ha−1 applied in January. Perennial ryegrass cultivars were compared using 50% inhibition (I50) values, i.e. 50% visible estimates of injury or 50% reduction in clipping weight. I50 values obtained 6 wk after treatment from injury data were 2.56, 2.64, 0.81, and 0.84 g ha−1 glyphosate for Replay, JS501, Caddy Shack, and Top Gun II, respectively. Replay and JS501 were similar in sensitivity to glyphosate and were up to four times more tolerant than Caddy Shack and Top Gun II across rating dates and data types.

Nomenclature: Glyphosate; annual bluegrass Poa annua L.; hybrid bermudagrass Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt Davy ‘Tifway'; perennial ryegrass Lolium perenne L. ‘Caddy Shack'; ‘JS501’; ‘Replay'; and ‘Top Gun II'.

Los cultivares de Lolium perenne ‘Replay’ y ‘JS501’ han sido mejorados convencionalmente para tener una sensibilidad reducida a glyphosate, potencialmente permitiendo el uso de este herbicida para el control selectivo de malezas en césped bermuda con L. perenne en sobre-siembra. Se realizaron experimentos de campo para evaluar la dosis de aplicación óptima de glyphosate, el régimen (aplicaciones sencillas o múltiples), y el momento de aplicación para el control de Poa annua en césped bermuda con sobre-siembra con estos cultivares de L. perenne. Adicionalmente, se realizaron experimentos de invernadero para comparar la sensibilidad a glyphosate de Replay y JS501 en relación con los cultivares susceptibles ‘Caddy Shack' y ‘Top Gun II' mediante análisis de respuesta a dosis usando modelos log-logísticos. En los experimentos de campo, solamente dos tratamientos resultaron en >90% de control de P. annua y <25% de daño de L. perenne. Estos dos tratamientos fueron una sola aplicación de 280 g ae ha−1 de glyphosate en Enero y 140 g ha−1 seguidos por otros 140 g ha−1 adicionales aplicados en Enero. Los cultivares de L. perenne fueron comparados usando valores de 50% de inhibición (I50), i.e. 50% de daño con base en estimaciones visuales o 50% de reducción en el peso del tejido foliar cortado durante la chapia. Los valores de I50 obtenidos 6 semanas después del tratamiento, con base en los datos de daño, fueron 2.56, 2.64, 0.81, y 0.84 g ha−1 de glyphosate para Replay, JS501, Caddy Shack, y Top Gun II, respectivamente. Replay y JS501 fueron similares en su sensibilidad a glyphosate y fueron hasta cuatro veces más tolerante

Michael L. Flessner, J. Scott McElroy, and Glenn R. Wehtje "Annual Bluegrass ( Poa annua) Control in Glyphosate-Resistant Perennial Ryegrass Overseeding," Weed Technology 28(1), 213-224, (1 January 2014).
Received: 28 June 2013; Accepted: 1 October 2013; Published: 1 January 2014

herbicide tolerance
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