Prodiamine is a dinitroaniline herbicide labeled for PRE control of goosegrass in warm-and cool-season turfgrass. In 2013, several golf course roughs in Maryville, TN reported poor goosegrass control (< 20%) following prodiamine treatment at 1,120 g ai ha -1. We harvested suspected prodiamine-resistant (PR) and prodiamine-susceptible (S) goosegrass phenotypes from the field and exposed them to a range of increasing prodiamine concentrations in hydroponic culture. Exposure to prodiamine at 0.001 mM reduced root growth of the S phenotype to 11% of the non-treated check. By comparison, exposure to 0.001 mM prodiamine had minimal effect on the PR phenotype, as root growth was 94% of the non-treated check. Molecular analyses revealed that PR plants contained a threonine (Thr) to isoleucine (Ile) substitution at position 239 on the α-tubulin 1 (TUA1) protein. The substitution, found in all PR plants, is the mechanism of prodiamine resistance in this phenotype. In field studies, topramezone controlled PR goosegrass 72% to 89% by 50 d after treatment (DAT) compared to only 22% to 23% for foramsulfuron. Topramezone treatment injured bermudagrass 34% to 60% from 7 to 14 DAT; however, injury was ≤6% 28 DAT and 0% by the end of the study. Our results indicate that POST applications of topramezone can control dinitroaniline-resistant goosegrass. In addition, we established an easy-to-use genotyping assay to quickly screen goosegrass phenotypes for a target-site mutation (Thr-239-Ile) on TUA1 associated with resistance to dinitroaniline herbicides such as prodiamine. Future research should work to expand this assay for use with other weed species and herbicidal modes of action. Nomenclature: Foramsulfuron; prodiamine; topramezone; goosegrass, Eleusine indica L. Gaertn.; bermudagrass, Cynodon dactylon L. Pers.
Poor annual bluegrass control was reported in golf course roughs following treatment with prodiamine (1120 g ai ha −1 ) and glyphosate (840 g ae ha −1 ) during hybrid bermudagrass dormancy. Research was conducted to determine if this annual bluegrass phenotype was resistant to both prodiamine and glyphosate and to determine the efficacy of herbicide mixtures for controlling this phenotype in the field. In PRE or POST dose-response experiments, 9 to 31 times more prodiamine or glyphosate was needed to control (or reduce dry biomass of) this resistant phenotype by 50% compared to an herbicide-susceptible phenotype. Moreover, glyphosate-susceptible plants accumulated 50% more shikimic acid (898 mg kg −1 ) 6 d after treatment than those resistant to glyphosate (394 mg kg −1 ). October (fall) applications of herbicide mixtures containing trifloxysulfuron, simazine, S-metolachlor, or mesotrione controlled this resistant annual bluegrass phenotype 84 to 98% in April (spring), with no differences detected among treatments. Our findings document the second instance of annual bluegrass evolving multiple resistance in a managed turfgrass system. However, several herbicide mixtures can be used to effectively manage this resistant phenotype. Nomenclature: glyphosate; mesotrione; prodiamine; simazine; S-metolachlor; trifloxysulfuron; annual bluegrass, Poa annua L.; hybrid bermudagrass, Cynodon dactylon × Cynodon transvaalensis Burtt-Davy. Key words: Turf, turfgrass, golf course, mitotic-inhibiting herbicide, EPSPS.Control limitado de Poa annua fue reportado en "roughs" de campos de golf después de tratamientos con prodiamine (1120 g ai ha −1 ) y glyphosate (840 g ae ha −1 ) durante el período de dormancia del césped bermuda híbrido. Se realizó una investigación para determinar si este fenotipo de P. annua era resistente a prodiamine y glyphosate y para determinar la eficacia de mezclas de herbicidas para controlar este fenotipo en el campo. En experimentos de respuesta a dosis con herbicidas PRE o POST, se necesitó de 9 a 31 veces más prodiamine o glyphosate para controlar (o reducir la biomasa seca) de este fenotipo resistente en 50% en comparación a un fenotipo susceptible a estos herbicidas. Además, plantas susceptibles a glyphosate acumularon 50% más ácido shikimic (898 mg kg −1 ) 6 d después del tratamiento que plantas resistentes a glyphosate (394 mg kg −1 ). Aplicaciones en Octubre (otoño) de mezclas de herbicidas que contenían trifloxysulfuron, simazine, S-metolachlor, o mesotrione controlaron este fenotipo resistente de P. annua 84 a 98% en Abril (primavera), sin detectarse diferencias entre estos tratamientos. Nuestros resultados documentan la segunda instancia de P. annua que evoluciona resistencia múltiple en un sistema manejado de céspedes. Sin embargo, varias mezclas de herbicidas pueden ser usadas para manejar efectivamente este fenotipo resistente.
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