Influence of Nitrogen, Plant Growth Regulators, and Ferrous Sulfate On Annual Bluegrass Populations.

Annual bluegrass (Poa annua L.; ABG) is widely adapted to various growing environments and is often considered a weed in creeping bentgrass (Agrostis stolonifera L.; CBG) putting greens.   Various management strategies have been implemented to eradicate or suppress the ABG, but its control has proven elusive.  The objective of this field study was to elucidate the ability of various nitrogen rates, ferrous sulfate rates and plant growth regulators to reduce ABG populations in a CBG putting green.  A two-year field study was initiated in 2010 on a research putting green with a mixed stand of ‘L-93’ CBG (~75%) and ABG (~25%) in University Park, PA.  Plots measured 0.9 x 1.8 m and were setup as a 2 x 3 x 3 factorial and arranged in a randomized completed block design with four replications.  Main factors included nitrogen (24 or 108 to 147 kg N ha^-1 year ^-1), ferrous sulfate (0, 12 and 49 kg Fe ha^-1 application^-1) and plant growth regulators (trinexapac-ethyl at 0.043 kg a.i. ha^-1, flurprimidol at 0.28 kg a.i. ha^-1 and none).  Treatments were initiated on 26 May 2010 and applied approximately every 3 weeks throughout the growing season in 2010 and 2011.  On the final rating date (12 Sept 2011), the main effect of nitrogen and plant growth regulators were significant.  Turf receiving low and high seasonal N had 32% and 37% ABG, respectively.  Turf treated with flurprimidol, trinexapac-ethyl and no plant growth regulators had 15%, 44% and 45% ABG, respectively.  The least percent ABG (6%) was observed within plots receiving 24 kg N^-1 year^-1 + flurprimidol + 49 kg Fe ha^-1 application^-1.  The greatest percent ABG occurred within plots receiving 24 kg N^-1 year^-1 + trinexapac-ethyl (57%).  The long-term impact of these programs on species composition and overall turfgrass quality remains unknown.