Control of Perennial Annual Bluegrass Biotypes with Postemergence Herbicides.

Annual bluegrass (Poa annua L.; ABG) is generally considered an undesirable species on creeping bentgrass (Agrostis stolonifera L.) putting greens due to its poor heat tolerance, increased disease susceptibility, and prolific production of seedheads.  Unfortunately, postemergent control of ABG is limited and limited information on herbicide efficacy on perennial ABG biotypes exists.  The objective of this study was to investigate the tolerance of perennial ABG biotypes to three herbicides.  A greenhouse study was conducted in the spring of 2011.  Mature plugs of six known perennial ABG biotypes were removed from the field and potted in a greenhouse.  Pots were arranged in a randomized complete block design with three replications.  Treatments included amicarbazone (0.147 kg a.i./ha), bispyribac-sodium (0.074kg a.i./ha), methiozolin (2.0 kg a.i/ha), and an untreated control.  All treatments were applied twice on a 14-day interval in 815 L H₂0/ha using a CO₂ backpack sprayer (276 kPa).  Severe injury to ABG was observed within 1 and 2 weeks following the first application of amicarbizone and bispyribac-sodium, respectively.  In general, near or complete death to all ABG occurred 2 weeks after the first and second application of amicarbizone and bispyribac-sodium, respectively.  Injury to the perennial biotypes of ABG treated with methiozolin was slow with most biotypes not exhibiting visual signs of injury until 2 to 3 weeks following the second application.  Although no biotypes died completely from the methiozolin rates applied, 5 out of 6 biotypes were nearly completely killed.  The remaining ABG biotype, however, only exhibited moderate injury. Results from this study indicate that postemergence control of perennial ABG biotypes may be possible, but tolerance among these naturally occurring ABG biotypes may exist.  Evaluation of 30 seeded perennial and annual ABG biotypes is currently being conducted.