Putting Green Annual Bluegrass Suppression with Flurprimidol, a Nitrogen Regime, and a Soil Surfactant.

Creeping bentgrass [Agrostis stolonifera L.: CBG] continues to be the preferred putting green species throughout the cool-humid region where a uniform, reliable and persistent surface is desired.  On older greens the uniformity can be disrupted by annual bluegrass (Poa annua L.: ABG) encroachment.  Managers utilize a variety of tools such as soil surfactants (SS), root-absorbed plant growth regulators (PGRs) like flurprimidol (FL) and/or modifications in fertility programs to favor CBG populations.  This two-year field study evaluated the influence of a commercial SS applied every 28 days, FL (0.28 kg a.i. ha^-1 every 14 days), two liquid applied fertilizer sources (46-0-0 vs. 20-20-20) at two nitrogen (N) rates (7.5 vs. 15 kg N ha^-1every 14 days) on a native-soil research green containing ≈30% ABG initially.  Products were foliar applied from early June through October of each year.  After two years, ABG populations were not affected by the SS and the greatest suppression occurred where FL was applied, decreasing ABG ≈60-85% from initial.  Where FL was not applied there was a strong fertilizer source and rate effect.  ABG populations decreased ≈25% when 46-0-0 was applied at either rate. By contrast, the application of 20-20-20 resulted in no ABG population changes for the low N rate and an ≈84% increase for the high N rate.  The interaction between soil moisture, PGR use and fertility regime continues to be complex, but worthy of further long-term study.