Influence of Nitrogen, Plant Growth Regulators, and Iron Sulfate on Annual Bluegrass (Poa annua L) Populations on a Golf Green

Annual bluegrass (ABG, Poa annua L.) is widely adapted to most growing environments and often is considered a weed on golf greens. Although numerous sustainable and low input management practices have been gaining popularity in the United States and around the world, limited to no research-based information is available on their ability to reduce ABG while promoting more desirable species such as creeping bentgrass (CBG, Agrostis stolonifera L.). The objective of this two year field study conducted in University Park, PA between 2010 and 2011 was to elucidate the interaction of two nitrogen (N) rates, two plant growth regulators (PGRs) and two iron sulfate (Fe) rates as they relate to reducing ABG  populations in a simulated   golf green.   Turf consisted of mature stand of ‘L-93’ CBG  (~75%) and ABG  (~25%).  Main factors included N from ammonium sulfate (21-0-0) (24, or 108 to 147 kg N ha^-1 year^-1),;the PGRs trinexapac-ethyl (TE;0.043 kg a.i. ha^-1 application^-1),and flurprimidol (FL; 0.28 kg a.i. ha^-1 application^-1), and Fe from iron sulfate (0, 12, or 49 kg Fe ha^-1 application^-1). Treatments were initiated in May and applied approximately every 3 wk for a total of 8 and 9 applications in 2010 and 2011, respectively. Annual bluegrass populations were determined using a grid system. The main effect of N and PGR had the greatest impact on ABG populations. Few differences in ABG populations existed among plots treated with TE or no PGR and populations averaged 44% in 2011. Turf within plots treated with FL had a seasonal average of 4 and 14% ABG in 2010 and 2011, respectively. Plots treated with the low N generally had lower ABG populations and an interaction with Fe only was observed in 2011. In 2011, ABG populations were negatively correlated with Fe rate in turf receiving 24 kg N ha^-1 year^-1, but not in plots treated with 147 kg N ha^-1 year^-1. Flurprimidol had the greatest effect in reducing ABG in the N x PGR x Fe  programs. Few, mostly agronomically insignificant  differences in soil pH or organic matter levels were observed among treatments. While ABG populations were reduced or maintained within select treatment combinations, the long-term impact on species composition and overall turfgrass quality remains unknown.