Effects of Seasonal Fertilizer Distribution on Turf Quality, Spring Green-up and Competition from Annual Bluegrass Poa Annua

Invasion of annual bluegrass (Poa annua L.) is a major concern on red fescue (Festuca rubra L.) putting greens. Our objective was to determine the effect of three seasonal fertilizer distribution treatments on red fescue turf quality and annual bluegrass encroachment. The experiment was conducted over 2 yr on a USGA-specified putting green at NIBIO Turfgrass Research Center Landvik, Norway (58° N). A complete liquid fertilizer was applied weekly for an annual nitrogen input of 11 g m⁻² in all treatments. In the FLAT rate treatment, the weekly fertilizer rate was 0.45 g N m⁻² wk⁻¹ from 5 May to 28 September. The FALL+ treatment received 0.68 g N m⁻² wk⁻¹ from 11 August to 28 September and 0.23 g N m⁻² wk⁻¹ from 5 May to 21 June, whereas the SPRING+ treatment was the opposite. The SPRING+ fertilization resulted in significantly better turf quality and significantly less annual bluegrass than the two other treatments in the second year of the study. The FALL+ fertilization gave higher quality ratings in the fall and early spring, but this effect came at the expense of more annual bluegrass. In conclusion, we recommend a fertilizer regime with the highest input from early May until midsummer to produce red fescue putting greens with the highest possible turfgrass quality and minimal encroachment by annual bluegrass.