Controlling herbicide resistant annual bluegrass (Poa annua L.) phenotypes with methiozolin

Authors: BROSNAN, JAMES - University Of Tennessee; VARGAS, JOSE - University Of Tennessee; BREEDEN, GREGORY - University Of Tennessee; BOGGESS, SARAH - University Of Tennessee; STATON, MARGARET - University Of Tennessee; Wadl, Phillip; TRIGIANO, ROBERT - University Of Tennessee

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2017
Publication Date: 6/28/2017
Citation: Brosnan, J.T., Vargas, J.J., Breeden, G.K., Boggess, S.L., Staton, M.A., Wadl, P.A., Trigiano, R.N. 2017. Controlling herbicide resistant annual bluegrass (Poa annua L.) phenotypes with methiozolin. Weed Technology. 31(3):470-476. https://doi.org/10.1017/wet.2017.13.
DOI: https://doi.org/10.1017/wet.2017.13

Interpretive Summary: Effective herbicides for annual bluegrass control are critically important to turfgrass managers given widespread reports of herbicide resistance in annual bluegrass. Researchers at the University of Tennessee and a USDA scientist at Charleston investigated the newly developed herbicide methiozolin for controlling herbicide resistant annual bluegrass. Methiozolin was used because it effectively controls annual bluegrass via a unique mode of action that is not thoroughly understood. To that end, glasshouse research was conducted to evaluate methiozolin efficacy for control of several herbicide resistant annual bluegrass individuals. All resistant individuals and a susceptible control were treated with variable rates of methiozolin. Methiozolin effectively controlled the annual bluegrass in most individuals with resistance to the herbicides glyphosate (also known as Roundup), prodiamine, and simazine. Interestingly, methiozolin failed to effectively control or reduce dry biomass of an individual with resistance to the herbicides trifloxysulfuron, simazine, and indaziflam. Our findings indicate that methiozolin may provide turf managers a tool for controlling select annual bluegrass phenotypes with resistance to glyphosate, simazine, or prodiamine.

Technical Abstract: Methiozolin is an isoxazoline herbicide being investigated for selective POST annual bluegrass control in managed turfgrass. Research was conducted to evaluate methiozolin efficacy for controlling two annual bluegrass phenotypes with target site resistance to photosystem II (PSII) or enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibiting herbicides (i.e., glyphosate), as well as phenotypes with multiple resistance to microtubule and EPSPS or PSII and acetolactate synthase (ALS) inhibiting herbicides. All resistant phenotypes were established in glasshouse culture along with a known herbicide-susceptible control and treated with methiozolin at 0, 125, 250, 500, 1000, 2000, 4000, or 8000 g ha-1. Methiozolin effectively controlled annual bluegrass with target site resistance to inhibitors of EPSPS, PSII, as well as multiple resistance to EPSPS and microtubule inhibitors. Rates required to reduce above ground biomass of these resistant phenotypes 50% (GR50 values) were not significantly different from the susceptible control, ranging from 160 to 421 g ha-1. Interestingly, methiozolin failed to control a phenotype with target site resistance to PSII and ALS inhibitors with GR50 values for the resistant and susceptible phenotypes measuring 863 and 423 g ha-1, respectively. Additional research using ribonucleic acid-sequencing technology is needed to determine if non-target site resistance mechanisms may be up-regulated in this phenotype following methiozolin treatment. Our findings indicate that methiozolin is an effective option for controlling select annual bluegrass phenotypes with target site resistance to several herbicides. However, turfgrass managers must continue to diversify strategies for annual bluegrass control to reduce selection pressure for phenotypes with either target or non-target resistance mechanisms.