Influence of Cultural Factors on Species Dominance in a Mixed Stand of Annual Bluegrass/Creeping Bentgrass

Annual bluegrass (Poa annua var. reptans (Hausskn.) Timm.) is a weedy species that is a component of most close-cut, irrigated fairways. Research was conducted to determine the effect of five management factors and their interactions on the species composition of a mixed stand of annual bluegrass and creeping bentgrass (Agrostis palustris Huds.) maintained at 13 mm. Soil was an Owosso-Marlette sandy loam (fine-loamy, mixed, mesic, Typic and Glossoboric Hapludalfs). Management factors investigated for 3 yr were irrigation (daily at 75% open pan evaporation (OPE), triweekly at 110% OPE, and at wilt); clipping treatments (returned or removed); N fertility (98 or 293 kg N ha⁻¹ yr⁻¹); plant growth regulator (PGR) treatments (mefluidide, N-[2,4-dimethyl-5-[[(trifluoromethyl)-sulfonyl] amino] phenyl] acetamide, at 0.14 kg ha⁻¹; EL-500, α-(1-methylethyl)-α-[4-(trifluoromethoxy)phenyl] 5-pyrimidine methanol, at 1.12 kg ha⁻¹ and a control) and ‘Penncross’ creeping bentgrass overseeded (49 kg ha⁻¹ yr⁻¹) or not overseeded). Changes in annual bluegrass (AB) populations for each growing season were determined utilizing the point quadrat method. The effect of clipping removal on AB seed in the soil was determined. Returning clippings increased annual bluegrass 12% over plots in which clippings were removed. Overseeding with creeping bentgrass (CB) increased CB populations 8% compared to plots irrigated daily at 75% OPE and not overseeded. Mefluidide in combination with high N fertility resulted in AB populations 8% higher than control or EL-500 plots at the same fertility level. Mefluidide also increased AB populations relative to control or EL-500 treatments when clippings were removed. The greatest significant decrease in AB (28%) occurred with the treatment combination of clippings removed, overseeded, and no PGR. Removing clippings reduced the number of viable AB seeds in the soil by 60%. Contribution from Dep. of Crop and Soil Sciences and the Michigan Agric. Exp. Stn., Journal Article no. 12527, Michigan State Univ.