Confirmation and Control of Annual Bluegrass Resistant to Photosystem‐II‐Inhibiting Herbicides

Abstract

An annual bluegrass (Poa annua L.) phenotype suspected to be resistant to photosystem II (PSII)‐inhibiting herbicides was identified in a zoysiagrass [Zoysia matrella (L.) Merr., cv. ‘Royal’] sod production field during 2013. Research was conducted during 2013 to 2015 to confirm if this phenotype (R) was resistant to PSII‐inhibiting herbicides and evaluate alternative herbicide options for effective preemergence control. In the glasshouse, treatment with the PSII‐inhibiting herbicide simazine at the maximum labeled rate for use in sod production (2240 g ha−1) only controlled this R phenotype 33%, and increasing the application rate to 9000 g ha−1 did not improve control. Comparatively, simazine controlled a known susceptible phenotype (S) 100% at both rates. DNA sequencing identified a genetic mutation in R annual bluegrass that resulted in a serine‐to‐glycine substitution at amino acid residue 264 on the D1 protein targeted by simazine. In the field, applications of simazine at rates of 140 to 9000 g ha−1 controlled R annual bluegrass ≤3% by 212 d after treatment. Applications of indaziflam (35, 52.5, and 70 g ha−1), oxadiazon (3350 g ha−1), prodiamine + sulfentrazone (844 + 416 g ha−1), and pendimethalin + dimethenamid‐P (2240 + 1686 g ha−1) controlled this R phenotype 98 to 100% and reduced plant counts similarly. Our findings confirm the presence of annual bluegrass in a zoysiagrass sod production field that is resistant to PSII‐inhibiting herbicides via target site mutation of the D1 protein. However, rotation to preemergence herbicides with alternative mechanisms of action to simazine can effectively control this phenotype. This marks the first reported case of herbicide‐resistant annual bluegrass in a sod production system. Management of this phenotype is critically important considering that harvesting and shipment of sod could potentially disseminate plants with target site mutations conferring resistance to PSII‐inhibiting herbicides over a wide geographical area.

Annual bluegrass (Poa annua) resistance to indaziflam applied early‐postemergence

“…For example, PRE applications of indaziflam at 52.5 to 70 g ha −1 controlled dinitroaniline‐resistant annual bluegrass 88–97% rated 180 days after treatment (DAT) . Similar responses have been reported following PRE applications of indaziflam to control annual bluegrass with resistance to acetolactate synthase (ALS) and photosystem II (PSII) inhibiting herbicides …”

“…This is a first report of annual bluegrass resistance to indaziflam applied early‐postemergence. Evolution of annual bluegrass with resistance to indaziflam is concerning given that the herbicide is an important tool for turfgrass managers controlling annual bluegrass with resistance to mitotic inhibitor, PSII‐, and ALS‐inhibiting herbicides . The scope of multiple resistance documented herein is perhaps more concerning given that annual bluegrass surviving EPOST treatment with indaziflam was also able to survive EPOST treatment with six other modes of action.…”

Herbicide-resistant weeds in turfgrass: current status and emerging threats

“…For example, Hutto et al (2004) identified simazine-resistant annual bluegrass on 43% of golf courses in Mississippi. Simazine resistance was also identified in annual bluegrass on a sod farm in Tennessee (Brosnan et al 2017b), which could perpetuate the issue over a wider geographical area. Moreover, annual bluegrass with multiple resistance to PSII inhibitors and other SOAs, particularly ALS inhibitors, has been reported (Brosnan et al 2015(Brosnan et al , 2016.…”

Annual bluegrass control in bermudagrass using dimethenamid and pendimethalin

“…In turfgrass, FreeHand effectively controlled simazine (6‐chloro‐2‐ N ,4‐ N ‐diethyl‐1,3,5‐triazine‐2,4‐diamine)‐resistant ABG when applied preemergence in a zoysiagrass ( Zoysia spp.) sod production field (Brosnan, Breeden, Vargas, & Grier, 2017).…”

“…A survey of ABG populations on 90 golf courses in Tennessee (representing 30% of the 297 courses in the state) revealed sizeable percentages of ABG that was resistant to glyphosate (64%), foramsulfuron (21%), prodiamine (58%), or simazine (97%) (Brosnan, Vargas, Breeden, & Zobel, 2020a). Several researchers have demonstrated that herbicide mixtures with several modes of action can be useful in managing herbicide‐resistant grassy weeds (Breeden et al., 2017; Brosnan et al., 2017; Busi, Powles, Beckie, & Renton, 2019).…”