The effect of daily treatment with UV light of turf grass greens infected by Sclerotinioria homoeocarpa and Microdochium nivale. Introduction In the Netherlands, golf is increasing in popularity and the present golf courses are occupying 7300 hectares in total (Zibb: Portal voor ondernemers. Tips, tools en het laatste nieuws). Turf grasses are plants that are made very susceptible to infection by fungi because of their prerequisites. Especially the greens have high demands: The grass should be kept very short and has to form a smooth surface with as little unevenness as possible.
Every time the grass is mowed, the plants are mechanically wounded and are therefore more easily penetrated by fungi. Throughout the year, turf grasses are dealing with a lot of different fungi, which all have a different ideal combination of factors to infect the grass. Sclerotinioria homoeocarpa or Dollarspot and Microdochium nivale or Snow Mold are the most common fungi and cause severe infections of greens. Dollarspot occurs from early spring till late autumn over the whole world.
Many species of turf grasses are susceptible to these fungi. We this fungus infects the grass, small, circular, straw coloured spots occur. These can reach a width of 15 cm (Couch, 3th edition). The fungus can be spread by human, animals, wind and water and gets active when dew occurs on the edge of the grass. Wet leaves also favourable for the fungus. (Smiley et al, 3th edition). Snow mold can occur in every month of the year and doesn’t exactly need a snow cover in order to be present. This fungus grows in cold and humid weather conditions.
In autumn and winter, when the grass doesn’t grow as fast or not at all, it is extremely susceptible to snow mold (Smiley et al, 3th edition). Many fungicides are used by golf keepers, but these are costly and often environmental damaging substances. Moreover, fungicides can only be used in restricted amounts in order to avoid that the fungi adapt genetically to and detoxify those chemicals. Making use of resistant cultivars is another approach but is not durable, because fungi can adapt themselves easily and their resistance is mostly broken within a few years.
UV light can damage and kill many micro organisms (figure 1). From research done by Wageningen University, it was proven that UV-C light can reduce the germination of spores of Phytophthora infestans (Kessel and Forch, 2006). Analogous, this would be also suitable for Sclerotinioria homoeocarpa and Microdochium nivale. Figure 1. The effect of UV light on the DNA of living organisms. When the applied dose is high enough, the DNA helix is destroyed or gets damaged, so in the end, the DNA is dysfunctional. (American Air & Water®, Inc. – UV Disinfection Systems).
With field trails, we want to test if a daily applied dose of UV light will reduce the symptoms of Dollar spot and snow mold. Field trials The field trials that are described in this report were conducted in October 2007 on a green of a golf court in Geijsteren and in November 2007 in Andersteijn. The green keepers cooperated by applying the UV light daily on the test plots of the greens. The Greens-Cleaner was put behind a gator and a few minutes before the treatment the lamps were turned on in order to function properly. The dose of UV we applied was ….. determined by former experiments … Field trial in Geijsteren (Dollarspot) Set up of the field trial The first trial was done on a green in Geijsteren, the Netherlands, where symptoms of Dollarspot could be clearly distinguished (figure 2). This trail was mainly conducted to determine the optimal duration of UV application: long enough to reduce the symptoms of the fungus, but not too long in order not to damage the grass. Figure 2. Symptoms of Dollarspot on the green in Geijsteren. In this trail, 7 plots of equal size were marked.
UV light was daily applied by the green keeper on 6 plots during two weeks. One plot was used as a control, so was not treated (figure 3). Every few days, pictures were taken to compare if reduction of the symptoms occurred. In the second week, the grass was not mowed anymore because of the start of the winter period, when the grass doesn’t grow for a while. Figure 3. Field trial in Geijsteren. In the green (circle), seven plots were marked. The applied dose of UV light was: 30 s, 45 s, 1 min, 2 min, 3 min and 4 min. One plot was used as a control(C). This plot was not treated.
Results From the first field experiment, the ideal dose was determined to use an as low as possible dose UVC light as possible. Discussion This experiment was done to determine whether a daily treatment of 15 seconds of the green with the Greens-cleaner, reduces the symptoms of fungal diseases. One should take notice that these experiments, done in autumn, have a less clear effect then when the experiments would have been done in spring or summer. In these months, more sunlight is present and the length of the light period is longer than in autumn or winter.
Therefore, grasses can’t grow as vigorously and can only recover very slowly from a pathogen attack. An important fact is that dew is amelioration the conditions for fungi to spread between plants by water. The ideal combination to prevent fungi from spreading though the green and to reduce the symptoms is to make use of a combined machine of a sweeper with the Greens-cleaner attached to it. It should be taken into account that the Greens-cleaner is an environmental friendly, durable manner to reduce the symptoms on greens, when applied daily, from the moment on when the first symptoms of a fungal disease are present.
Field trial in Andersteijn (Snow mold) Set up of the field trial The purpose of this trial, done in Andersteijn, the Netherlands, was to find out if the Greens Cleaner, also effective on a green where Snow Mold is present (figure 4). Another thing that was considered was if a daily treatment of 15 seconds with UV light is sufficient to reduce the symptoms. ? Figure 4 Symptoms of Snow mold on the green in Andersteijn. In total, five plots were marked on the green and three indications were made to point the position of the tripod.
During two weeks, the treatment with UV light was conducted between 13. 00 and 13. 30 h. Four plots were daily treated for 15 seconds with UV light with the Greens Cleaner and one plot was not treated and was the control (figure 5). Straight afterwards, a picture was taken from the same position every day (figure 6). Figure 5 Field trial in Andersteijn. In the green (circle), five plots were marked. Plots 1-4 were daily treated for 15 seconds with UV light. One plot was used as a control(C). This plot was not treated.
Figure 6 Indication of the position of the tripod on the green in Andersteijn. Results In this field trial, differences were seen between the treated and non-treated plots, but it was not clear whether there was a true reduction of the symptoms on the treated plots, because of the season. Discussion Many fungi that are harmful to turf grasses occur on the surface of the plant. Treating infected greens with the Greens Cleaner is an environmental friendly and durable method to treat fungi like Dollarspot and Snow mold.
When symptoms of fungi appear a daily treatment with the Greens Cleaner can be applied. It is not clear yet how many seconds the grass has to be treated because the duration of an effective treatment to destroy the fungus and its spores depend on the type of fungus. It is also important that when the Greens Cleaner is used in spring and summer, the reduction of the symptoms will be much clearer than in autumn and winter. The reason for this is the reduction of daylight and temperature from autumn on.
The grass will therefore not be able to fulfil photosynthesis as effective and won’t grow and recover as fast as in spring or summer. This is also the reason why grass is not mowed from late fall onwards. Plants can recover only slowly after infection by pathogens, even if the mycelium of the fungus is destroyed by UV treatment. When dew is present, the conditions for the production and spread of spores of Dollarspot and Snow mold are very favourable, so a combination of the Greens Cleaner with a sweeper would be an appropriate manner to reduce the activity of fungi on turf grass.
The Greens Cleaner destroys the mycelium and mostly spores of fungi and the sweeper can prevent the spread of the surviving spores via dew. Experiments will be done that are statistically correct to attribute the treatments randomly, which will give more detailed conclusions. This survey will be done in spring, so we can look how fast the turf grass recovers form the disease symptoms of fungi after UV treatment.
Literature list 1American Air & Water®, Inc. – UV Disinfection Systems. http://www. americanairandwater. com/uv-facts/germicidal-uv. tm Gevonden op 8-12-2007. 2Couch, H. B. Diseases of turfgrasses 3e editie. 3Kessel, G. J. T and Forch, M. G. Effect of UV-exposure on germination of sporangia of Phytophthora infestans. (2006) Plant Reseach International B. V. , Wageningen 4Smiley, R. W, Dernoeden, P. H, Clarke, B. B. Compendium of turfgrass diseases, 3e editie 5Zibb: Portal voor ondernemers. Tips, tools en het laatste nieuws. http://www. zibb. nl/web/Bedrijfsvoering/management/Nieuws/Management-nieuwsbericht/Aantal-golfbanen-explosief-gestegen. htm Gevonden op 8-12-2007