A Biotype of Annual Bluegrass (Poa annua) in Tennessee Is Resistant to Inhibitors of ALS and Photosystem II

Abstract

Annual bluegrass resistance to inhibitors of acetolactate synthase (ALS) and photosystem II (PSII) in managed turf has been confirmed in the southeastern United States. A biotype of annual bluegrass that had developed resistance (R) to the PSII inhibitor simazine was not controlled by POST applications of foramsulfuron or trifloxysulfuron in 2011 or 2012. In whole plant dose-response experiments, trifloxysulfuron, simazine, and indaziflam controlled a susceptible (S) population of annual bluegrass > 91% when applied POST to nontillering plants. However, trifloxysulfuron applications at 3.5 to 223 g ai ha−1only controlled R annual bluegrass ≤ 40%. Similarly, simazine at 140 to 9,000 g ai ha−1only controlled R annual bluegrass ≤ 20%. R annual bluegrass plants were more tolerant to indaziflam applied POST to leaf stage plants prior to tillering, as rates > 100 g ai ha−1were needed to control R annual bluegrass ≥ 96%. No differences in the activity of ALS in R and S plants exposed to increasing foramsulfuron concentrations from 0 to 100 µM were detected suggesting that nontarget mechanisms could explain reduced efficacy of POST herbicide applications in whole plant dose-response experiments. Applications of indaziflam (35 to 70 g ha−1) and oxadiazon (2,240 to 4,500 g ai ha−1) effectively controlled R annual bluegrass when applied PRE. This biotype of R annual bluegrass is the first reported instance of a weed developing resistance to multiple modes of action in managed turf. Education is needed among turf managers regarding the consequences of exclusive use of the same herbicides for annual bluegrass control leading to the onset of herbicide resistance.

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 …”

A new amino acid substitution (Ala-205-Phe) in acetolactate synthase (ALS) confers broad spectrum resistance to ALS-inhibiting herbicides

“…Globally, annual bluegrass populations have developed resistance to nine different herbicidal mechanisms of action; however, instances of a single population developing multiple resistance are limited (Heap 2014 ). A population of annual bluegrass resistant to ALS and PSII inhibiting herbicides (POAAN-R3) was identified on a golf course in Memphis, Tennessee (Brosnan et al 2015 ). Trifloxysulfuron applications at rates as high as 223 g ha −1 only controlled POAAN-R3 ≤40 %.…”

“…Analysis of the genes coding for the target sites of ALS and PSII inhibiting herbicides in POAAN-R3 is needed to further elucidate mechanisms endowing resistance to trifloxysulfuron and simazine in this population (Brosnan et al 2015 ). Considering previous reports of weed species having multiple mutations associated with ALS herbicide resistance (Warwick et al 2008 ; Yu et al 2008 ), we hypothesize that POAAN-R3 will contain multiple target site mutations conferring resistance to ALS and PSII inhibitors.…”

Target-site Mutation and Fitness Cost of Acetolactate Synthase Inhibitor-resistant Annual Bluegrass

“…Annual bluegrass (Poa annua) is considered a most problematic annual winter weed in managed turfgrass, such as golf courses (Cross et al, 2013). This weed has traditionally been controlled by herbicides; however, populations that are resistant to various herbicides have been identified and studied (Brosnan et al, 2015;Heap, 2017;Kelly et al, 1999;McElroy et al, 2013). In the United States, P. annua accounts for more than half of reported herbicide resistance in managed turfgrass system since the 1980s, including populations resistant to photosystem II inhibitors, microtubule inhibitors, 5-enolpyruvylshikimate-3-phosphate synthase inhibitors, and, most recently, ALS inhibitors (Heap, 2012).…”

“…In the United States, P. annua accounts for more than half of reported herbicide resistance in managed turfgrass system since the 1980s, including populations resistant to photosystem II inhibitors, microtubule inhibitors, 5-enolpyruvylshikimate-3-phosphate synthase inhibitors, and, most recently, ALS inhibitors (Heap, 2012). Since 2012, the number of biotypes of P. annua resistant to ALS inhibitors has been increasing faster than any other mechanisms of action, resulting in resistant populations in Tennessee, Alabama, South Carolina, and Georgia (Brosnan et al, 2015;Heap, 2012). Annual bluegrass biotypes resistant to ALS inhibitors have not been documented previously in Mississippi.…”