Influence of Chemical and Cultural Management Strategies On Annual Bluegrass Populations On Golf Course Putting Greens.

Annual bluegrass (Poa annua L.; ABG) is often considered a weed within creeping bentgrass (Agrostis stolonifera L.; CBG) putting greens.  Management practices designed to eradicate or suppress the species have been met with limited success.  The objective of this field study is to elucidate the interactions of cultural and chemical management strategies on ABG populations using various rates of nitrogen, ferrous sulfate and plant growth regulators.  Four field studies were initiated in 2010 on a research putting green with a mixed stand of ‘L-93’ CBG and ABG (~25%). All trials were conducted at the Joseph Valentine Turfgrass Research Center located in University Park, PA.  Plots measured 0.9 x 1.8 m and were arranged in a randomized complete block design four replications.  The four studies consisted of either a 2 x 3 or 2 x 3 x 3 factorial with main factors of nitrogen (N) (0, 25, or 107 kg N/ha/year), plant growth regulators (PGR) (none, trinexapac-ethyl or flurprimidol), and ferrous sulfate (Fe) (0.0, 12, or 49 kg Fe/ha applied every three weeks).  Treatments were initiated on 26 May 2010 and applied approximately every 3 weeks throughout the growing season in 2010 and 2011.  All treatments were applied in 4073 L H₂O/ha using a CO₂ backpack sprayer (345 kPa).  Ongoing results have shown a wide range of seasonal ABG populations within treatments.  In the three-way factorial study (most recent rating date), treatments resulting in the least and greatest percent ABG had an average of 2% and 58%, respectively.  Overall, plots treated with flurprimidol have shown the greatest suppression of ABG populations when compared to other treatments.  Plots receiving low seasonal N applications (25 kg N/HA/year) generally had lower ABG populations when compared to those receiving 107 kg N/HA/year.  Ferrous sulfate (all rates and combinations) had little impact on ABG populations, but it was effective at improving turf color.