Are more or less fungicide applications needed on greens covered by plastic than on uncovered greens?

December 1, 2022

By Trygve S. Aamlid1, Jørgen Hornslien1, Trond Pettersen1 and Guttorm Tuxen2,
1Norwegian Institute of Bioeconomy Research (NIBIO) Turfgrass Research Group, 2Bærum Golf Course, Norway

Two weeks ago, between November 15 and 20, 2022, almost 30 of Norway’s 172 golf courses covered their greens with impermeable plastic sheets before the winter. The practice is based on four years of positive experiences in field trials at NIBIO Apelsvoll Research Center and on four golf courses in the Oslo region. More detailed information about this successful practice resulting in significantly less damage from ice and melting water can be found in earlier WinterTurf blog posts (Scandinavian research shows better winter survival with impermeable covers on golf course putting greens and Good turnout to study winter survival of greens at NIBIO Apelsvoll, Norway).

Current practice on Norwegian golf courses

One highly relevant question asked by many superintendents this fall has been whether the new practice of using impermeable covers increases or decreases the need for fungicide applications before winter?  Until October this year, only Delaro (prothioconazole + trifloxystrobin, i.e. systemic ingredients) and Medallion (fludioxonil, in practicality a contact fungicide) have been available for use on Norwegian golf courses. The new product Ascernity (difenokonazole + benzovindiflupyr) was approved in October as an alternative to Delaro, but too late to reach any widespread use before the winter.

As insurance, we have so far recommended superintendents who plan to cover their greens to make two or three fungicide applications prior to coverage. This is slightly more than in traditional greenkeeping without covers, in which a survey showed that 44% of Norwegian golf courses didn’t spray their greens at all, 43% sprayed once or twice and only 13% sprayed three times or more (Økland et al. 2018). Based on multiple experiments from about ten years ago, a rule of thumb for Scandinavian superintendents has been that one, two and three fungicide application in the fall reduce the snow mold infection in spring by about 65, 90 and 100%, respectively, as compared with an unsprayed control (Aamlid et al. 2015).

More disease close to ventilation pipes?

two different golf course greens with dead spots due to disease
Figure 1. Photos taken in April 2021 after removal of impermeable covers at Holtsmark (left) and Bærum (right) golf courses. Superintendents had a feeling there was more disease close to the 4” perforated drainage pipes used for ventilation under the covers. Photos by Mads Thers (left) and Guttorm Tuxen (right).

During the winter 2020-21, two of the four pioneering golf courses using impermeable covers reported they had more microdochium patch close to ventilation pipes than elsewhere under the covers (Figure 1). The question came up whether Microchium nivale and Typhula sp., both aerobic fungi, can be inhibited by the lower O2 concentrations and increased CO2 concentrations under the covers. If so, this would be in line with a Canadian study by Stricker et al. (2017) who observed 34% less development of microdochium patch at 800 than at 400 ppm CO2. In our studies at Apelsvoll and on the four Norwegian golf courses, CO2 levels under the covers have usually been higher than 40,000 ppm during most of the winter, while O2 concentrations have occasionally been lower than 5% without any negative impact on the survival of either creeping bentgrass or annual bluegrass (Aamlid et al. 2021).  Could it be that Microdochium nivale and Typhula sp. rea more sensitive to high CO2 / low O2 levels than the grass that we want to preserve and protect? And if so, could it be that impermeable covers – including continuous and careful control of gas concentrations under them – will reduce rather than increase the need for fungicide applications before winter?

New experiments

a golf course green with a white plastic cover
Figure 2. Experimental green at Bærum divided into four quadrants. Photo taken on November 16, 2022 by Guttorm Tuxen.

To answer these questions, we have initiated field trials on a mixed Poa/bentgrass green at Bærum GC (close to Oslo) and on a pure Poa green at NIBIO Landvik turfgrass research center on the Norwegian south coast. The experimental design is a 4-replicate split plot with plastic cover vs. no cover as main plots. For practicality, main plots with covers have been placed adjacent to each other, thus yielding a green with four quadrats (Figure 2). Within each main plot, there are subplots with either 0, 1, 2 and 3 fungicide applications from late September up to the last application shortly before coverage. Sensors for temperature, O2 and CO2 have been dug into the thatch/mat layer on all main plots and gas concentrations are monitored closely. As of December 1, two weeks after coverage (Figure 3), O2 concentrations on covered plots at Bærum GC have declined to around 13%, while CO2 concentrations have increased to 30,000 ppm (3%). The green was covered by snow four days after coverage, but temperature have been rather unstable after that. We are now excited to follow gas concentrations during the winter and see what the implications for snow mold attacks in spring will be. Reports will follow – stay tuned!

a graph showing percent oxygen declining over time and a second graph showing carbon dioxide increasing over time
Figure 3. Concentrations of O2 and CO2 on plots covered with plastic on November 16, 2022 at Bærum GC, Norway.


Aamlid, T.S., M. Thers, G. Jagger, G.R. Tuxen & J. Bentley 2021. Impermeable plastic covers for better winter survival of golf course putting greens: Ventilations under the covers during the winter 2020-2021. NIBIO Report 7(181): 1-55.

Aamlid, T.S., W.M. Waalen & T. Espevig 2015. Fungicide strategies for the control of turfgrass winter diseases. Acta Agriculturae Scandinavica, Section B — Soil & Plant Science 65: 161-169.  

Økland I., A. Kvalbein, W.M. Waalen, L. Bjørnstad, T.S. Aamlid & T. Espevig 2018. Winter injuries on golf greens in the Nordic countries (part 2). Survey of causes and economic consequences. Popular Scientific Article - STERF. 12 pp.

Stricker, S., T. Hsiang & A. Bertrand 2017.  Reaction of Bentgrass Cultivars to a Resistance Activator and Elevated CO2 Levels When Challenged with Microdochium nivale, the Cause of Microdochium Patch.  Int. Turfgrass Soc. Res. J. 13:1–4 (2017).