Amicarbazone for Annual Bluegrass Control in Creeping Bentgrass Putting Greens.

     Annual bluegrass is a common and troublesome weed in bentgrass putting greens.  Currently, there are no effective postemergent herbicides labeled for annual bluegrass control in bentgrass putting greens.  Research trials were initiated to evaluate sequential applications of amicarbazone late summer, fall or spring for annual bluegrass control and creeping bentgrass tolerance. 

      Evaluated bentgrass cultivars included ‘A1’, ‘A4’, ‘Crenshaw’, ‘G6’, ‘L93’ and ‘Penncross.’  Treatments were applied at 304 l/ha, replicated four times and utilized 4.5 m² plots.  Evaluated amicarbazone rates ranged from 49 – 123 g/ha.  Data collected included visual estimates of annual bluegrass control and bentgrass phytotoxicity.

                 Single amicarbazone (70WG) applications applied early September through mid-October did not provide annual bluegrass control through spring, regardless of application rate.  Partial annual bluegrass control (50%) was obtained with early November sequential applications (123 g/ha).  Further research trials indicate amicarbazone (49 g/ha) applied four times on weekly intervals beginning in spring may provide >80% annual bluegrass control while causing minimal bentgrass injury (≤11 %).  Other treatments including two applications at 61 or 92 g/ha did not provide consistent annual bluegrass control across trial locations.  Three applications (61 g/ha) did not provide adequate annual bluegrass control while three applications (91 g/ha) provided good annual bluegrass control although bentgrass response was not consistent across trials with some exhibiting unacceptable injury.  These data indicate amicarbazone (49 g/ha) applied four times on weekly intervals may provide selective control of annual bluegrass in creeping bentgrass putting greens.  Other application regimes may also provide selective annual bluegrass control although application timing and rate may need to be refined.