Overseeding of Fairways – A strategy for finer turf with less broad-leaved weeds and Poa annua.

Research concerning management of golf courses has so far concentrated on golf greens rather than fairways. Legislation regarding pesticide reduction in the Nordic countries will cause serious problems with annual bluegrass (Poa annua) and broadleaved weeds in years to come. Establishing a strong competitive turfgrass sward might be one solution to avoid massive invasion of weeds. This can be accomplished with an appropriate overseeding strategy adapted to the Nordic countries. Therefore, more information regarding the optimal overseeding strategy in the Nordic countries is crucial in order to create a strong fairway with a minimum of annual bluegrass and broadleaved weeds.

The aim of the project was to test a variety of parameters that might influence the outcome of an overseeding procedure. This includes overseeding date (spring or autumn), fertilisation when overseeding and turfgrass species; perennial ryegrass (Lolium perenne), red fescue (Festuca rubra) and Kentucky bluegrass (Poa pratensis) sown as single species.

The experiment was performed on an experimental fairway at Landvik (NIBIO, Norway) and on three golf courses in Denmark (Korsør, Skovbo and Hornbæk) in the period 2011- 2013 and with recording in 2014. Recording was on grass species composition and on weed occurrence, and in the Norwegian trial visual appearance was scored. In addition, the economic costs of the overseeding procedure were estimated for a standard golf course (18- hole course).

The main findings were that perennial autumn overseeding to be more successful, especially with the fertiliser but also on all times and with and without fertiliser when perennial ryegrass was introduced.

In the Norwegian experimental fairway, red fescue was also successfully introduced. On the three golf course fairways in Denmark this could not be demonstrated. For Kentucky bluegrass there was no indication of establishment after three years of overseeding. These findings may be partly due to the highly variable soil conditions that exist on golf fairways. The area at the research station in Norway is much more homogeneous. Another explanation is the use of topdressing and irrigation after overseeding in the Norwegian trial.

Overseeding for a 3-year period was not a successful strategy for control of broadleaved weeds and Poa annua. The amount of weeds was not reduced by the overseeding procedure after the 3-year period.

Recorded appearance, density etc. in the Norwegian trial did not demonstrate a significant effect of any of the treatments. A small increase in appearance and density was seen shortly after the spring overseeding in the perennial ryegrass plots, but the effect was not pronounced over the growing season.

The economics of overseeding were calculated because this is an issue. Today, the costs of overseeding are significant for most golf courses, especially if topdressing is included in order to increase the success. The question is whether it is necessary to overseed the whole golf course. A solution if money is limited could be to overseed selected areas where the turf is poor and open.