Abstract
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.
Highlights
Goosegrass is a summer annual weedy grass that is problematic throughout warm- and cool-season turfgrass (McCullough et al 2013)
Goosegrass germination is stimulated by fluctuating air temperature and light, with optimal germination observed following 16 h at 20°C and 8 h at 35°C with light (Nishimoto and McCarty 1997). Dinitroaniline herbicides such as prodiamine and pendimethalin are frequently used PRE to control annual weeds such as goosegrass in managed turfgrass systems
Topramezone, a hydroxyphenyl-pyruvate-dioxygenase inhibitor, is a pyrazole herbicide labeled for POST goosegrass control in turf at rates of 12.3 to 36.8 g ai ha-1 (Anonymous 2015)
Summary
Goosegrass is a summer annual weedy grass that is problematic throughout warm- and cool-season turfgrass (McCullough et al 2013). Goosegrass germination is stimulated by fluctuating air temperature and light, with optimal germination observed following 16 h at 20°C and 8 h at 35°C with light (Nishimoto and McCarty 1997) Dinitroaniline herbicides such as prodiamine and pendimethalin are frequently used PRE to control annual weeds such as goosegrass in managed turfgrass systems. These herbicides prevent microtubule polymerization in cells of susceptible species by binding to the globular protein tubulin (Vaughn et al 1991). Topramezone and foramsulfuron may provide turf managers with options for controlling dinitroanilineresistant goosegrass POST. Our objectives were to (1) determine the sensitivity of a putative PR goosegrass phenotype collected from this location, (2) elucidate the mechanism of resistance in this phenotype, and (3) identify options for effective POST control of this phenotype in the field
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