Influence of Nitrogen, Plant Growth Regulators, and Iron Sulfate on Annual Bluegrass Populations on a Golf Green

Abstract

Annual bluegrass (ABG, Poa annua L.) is often considered a weed on golf greens. Although numerous sustainable and low‐input management practices have gained popularity, 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 2‐yr field study was to elucidate the interaction of nitrogen (N) rates, plant growth regulators (PGRs), and iron sulfate (Fe) rates as they relate to reducing ABG populations in a golf green. Turf consisted of a mature stand of ‘L‐93’ CBG (∼75%) and ABG (∼25%). Factors included N from ammonium sulfate (21 N‐0 P‐0 K) (24 or 108–147 kg N ha−1 yr−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 in 2010 and 2011. Plots receiving 24 kg N ha−1 yr−1 received only four applications during the season. The effect of N and PGR was greatest on ABG populations. Few differences in ABG populations existed among plots treated with TE or no PGR. Turf within plots treated with FL had a seasonal average of 4 and 14% ABG in 2010 and 2011, respectively. Plots treated with 24 kg N ha−1 yr−1 generally had lower ABG populations. In 2011, ABG populations were negatively correlated with Fe rate in turf receiving 24 kg N ha−1 yr−1, but not in plots treated with 147 kg N ha−1 yr−1. Flurprimidol had the greatest effect on ABG populations in the N × PGR × Fe programs. Few differences in soil pH or organic matter levels, mostly agronomically insignificant, were observed among treatments. While ABG populations varied among select treatment combinations, the long‐term impact on species composition and overall turfgrass quality remains unknown.