Abstract
EU requirements for Integrated Pest Management (IPM), perhaps even pesticide-free management, have implications for choice of turfgrass species and varieties for golf courses. This paper reports results from variety testing for putting greens in the southern Nordic zone comprising Denmark and coastal areas in south Sweden and south Norway, and the northern zone comprising Finland, Iceland and remaining regions of Sweden and Norway. Forty-one varieties of seven species/subspecies were compared from 2007 to 2010 at Apelsvoll (Norway, 61° 42′ N, 250 m asl) and Korpa (Iceland, 64° 09′ N, 30 m asl) (northern zone), and at Landvik, (Norway, 58° 11′ N, 12 m asl) (southern zone). Once established, the trials were mowed at 3 mm for Agrostis and 5 mm for Festuca, Poa and Lolium. Mean fertilizer rates were 1.7 kg N 100 m−2 yr−1 to A. stolonifera and 1.0 kg N 100 m−2 yr−1 to other species. No pesticides were used. On average for varieties within species, F. rubra, especially ssp. commutata, had significantly less winter damage (biotic and abiotic) than L. perenne and Agrostis sp. F. rubra also had significantly less in-season diseases (mainly Microdochium patch) than A. capillaris and A. canina in the southern zone and in comparison with all Agrostis sp. in the northern zone. On average for varieties, the ranking based on overall visual merit was F. rubra ssp. commutata>F. rubra ssp. litoralis>A. canina>A. stolonifera>A. capillaris>P. trivialis>L. perenne in the northern zone, and A. canina>A. stolonifera>F. rubra ssp. commutata>F. rubra ssp. litoralis>A. capillaris>L. perenne>P. trivialis in the southern zone. For pesticide-free management of putting greens, we recommend pure seed blends or F. rubra in both zones. Seed blends of A. stolonifera or A. canina, and seed mixtures of F. rubra and A. capillaris are compatible with IPM including limited fungicide use. Ranking lists of varieties are presented.
Introduction
Restrictions in pesticide use are a major challenge facing the European turfgrass sector. The Directive 2009/128/EG of the European Parliament, which is now under implementation in most European countries, points to Integrated Pest Management (IPM) as a way of reducing the impact of pesticides on human health and the environment. Article 12 of this directive has a special focus on golf courses, recreational parks, sport grounds and other areas open to the public. For such areas, even a total ban of pesticide has been discussed. On golf courses, these regulations will have implications not only for turfgrass management, but also for the selection of turfgrass species and varieties.
As insect pests are relatively rare, most pesticides used on Nordic golf courses are either herbicides or fungicides. Herbicides are primarily used for control of broadleaved weeds, particularly on fairways (DGU 2011). Golf greens are usually established using pure sand, sand/peat, or sand/compost mixtures with no inherent seed bank, but the grass weed annual bluegrass (Poa annua) often invades from surrounding foregreens and fairways. Another group of weeds that has become more prevalent due to lower mowing heights, reduced fertility levels and milder winters with more rainfall are the mosses (Frahm Citation2010).
Turfgrasses growing on golf greens are exposed to ball marks, wear from players and machinery, and daily mowing to 3–5 mm. This stressful environment makes the turf vulnerable to diseases. Based on data from Scandinavia's largest turfgrass diagnostic laboratory, the most widespread turfgrass diseases are pink snow mould and Microdochium patch, both caused by Microdochium nivale (M. Usoltseva, pers. comm. Nov. 2010). Besides overall winter survival, tiller density and other characters affecting playing quality, resistance to these and other diseases have to be major criteria when selecting turfgrasses for Nordic golf greens. Further development of a more sustainable golf sector also requires the selection of turfgrass species and varieties that require less irrigation water, less fertilizer inputs and less mowing causing CO2 emission.
Variety testing of amenity grasses in the Nordic countries has a long tradition (Molteberg and Aamlid Citation2007), but systematic evaluation of turfgrass varieties on golf greens has only been carried out since 2003. Results from the first test round from 2003 to 2006 were reported by Aamlid and Molteberg (Citation2011). In this paper, we report results from evaluation of turfgrass species and varieties at three experimental sites from 2007 to 2010.
Materials and methods
Entries
In January 2007, breeding companies and their representatives were invited to enter varieties into the project. A total of 35 varieties representing seven species/subspecies were entered (). In addition, the six best varieties of the red fescues and bentgrasses from the previous test round (Aamlid and Molteberg Citation2011) were included as controls. There was no control variety of rough bluegrass or perennial ryegrass since these species had not been included in the previous test round.
Table I. Species and varieties tested in green trials 2007–2010. C = Control variety.
Experimental sites, weather data and the need for reseeding
Based primarily on the risk for abiotic and biotic winter damages, the Nordic countries are divided into one northern and one southern zone for turfgrass variety testing (Skjelvåg Citation1998, Molteberg and Aamlid Citation2007, Aamlid and Molteberg Citation2011). The trials sites Bioforsk Landvik, Norway (58° 20′ N, 12 m asl) in the southern zone, and Bioforsk Apelsvoll, Norway (60° 42′ N, 250 m asl) and Korpa Golf Course, Iceland (64° 09′ N, 30 m asl) in the northern zone are indicated in . Although in the same zone, Apelsvoll has a continental climate with hot summers and cold winters, while Korpa has an oceanic climate with cool summers and mild winters (). The 30-year (1961–90) annual precipitation average is 1230 mm at Landvik, 600 mm at Apelsvoll and 801 mm at Korpa. At the start of the project we also had a fourth trial site at Östra Ljungby Greenkeeper School in southern Sweden, but this trial was closed in 2008 as the school moved to another location. Results from Östra Ljungby are not reported here.
Figure 1. Map of the five Nordic countries showing the two major climatic zones and the experimental sites Landvik, Apelsvoll and Korpa. The trial at Östra Ljungby was discontinued in 2008.
Table II. Mean monthly temperature during the experimental period July 2007 – Oct. 2010 as compared with 30-year normal values (1961–90) at Landvik (southern climatic zone) and Apelsvoll and Korpa (northern climatic zone).
During the course of this project, Landvik had a snow cover of more than 6 weeks duration only during the winter 2009/10. The other winters had temperatures above the 30-year normal values. There were heavy snow falls on unfrozen soil resulting in pink snow mould, but the turfgrass plots always recovered by themselves and never had to be reseeded.
At Apelsvoll the winters 2007/08 and 2008/09 were milder than the 30-year normal values (), but unstable with intermittent snow and rain and temperature fluctuations causing long-lasting ice covers. Despite a good establishment in 2007, all varieties of perennial ryegrass, rough bluegrass, creeping bentgrass and colonial bentgrass had to be reseeded in spring 2008. Only chewings fescue, slender creeping red fescue and velvet bentgrass survived sufficiently to be able to recover without reseeding. The winter 2008/09 was even more severe, taking its toll on all species and requiring reseeding of all plots in spring 2009. The winter 2009/10 had a stable snow cover from 30 Nov. to 15 April and no mild spells causing ice formation; during this winter all plots survived although some were set back by snow mould.
The experiment at Korpa, Iceland, was never exposed to long-lasting snow or ice covers, but there were winter stresses caused by temperature fluctuation and heavy winds drying out the turf. Because of late seeding and lower summer temperatures () requiring a longer grow-in period than at Landvik and Apelsvoll, rough bluegrass and the three bentgrass species did not establish adequately. Combined with winter damage, this resulted in a need for reseeding of these species in spring 2008. No reseeding was necessary after the winters 2008/09 and 2009/10.
Experimental design and turfgrass management
The trials were established according to split-plot designs with three blocks (replicates), species on main plots and varieties on subplots. This allowed different management of the various species. Plot size was 1.0 m×1.0 m. Seeding dates in 2007 were 26 June at Apelsvoll, 11 July at Landvik and 17 August at Korpa. Seeding rates of bentgrasses, rough bluegrass, red fescues and perennial ryegrass were 0.5, 1.5, 3.0 and 4.0 kg 100 m−2, respectively. The same seeding rates were used when reseeding was necessary.
The trials at Landvik and Apelsvoll were mowed 3 times a week to a height of 3.0 mm for bentgrasses and 5.0 mm for red fescues, rough bluegrass and perennial ryegrass. Higher mowing was practised during grow-in, after reseeding, and at the beginning and end of each growing season. Because of the slow establishment and risk for wind erosion, the trial at Korpa was mowed at 20 mm in 2007 and 2008. In 2009, mowing height was gradually reduced from 12 mm in early spring to 5.5 mm by the middle of August, the same height for all species. In 2010, mowing started at 5 mm for all species in spring but was gradually reduced to 3 mm in the bentgrasses. At all experimental sites, mowing was carried out with walk-behind mowers and clippings collected.
The trials received inorganic fertilizers at 2-week intervals at Apelsvoll and Landvik and at 2–4 intervals at Korpa. Except at Korpa in 2007 and 2008, higher rates were given to creeping bentgrass than to red fescues, perennial ryegrass, velvet bentgrass, colonial bentgrass and rough bluegrass. On average for 2008, 2009 and 2010, seasonal rates to the two groups were 1.6 and 0.8 kg N 100 m−2 at Landvik and 1.7 and 0.9 kg N 100 m−2 at Apelsvoll. At Korpa, nitrogen rates to the two groups were 1.6 and 1.6 kg N 100 m−2 in 2008, 1.8 and 0.9 kg N 100 m−2 in 2009 and 2.4 and 1.3 kg N 100 m−2 in 2010. The mineral fertilizers also contained phosphorus, potassium and other macronutrients and micronutrients at balanced rates (Ericsson et al. Citation2012a, Citation2012b). Seasonal fertilizer distributions typically followed an asymmetric curve with the highest inputs in late May and June.
The experimental greens at Landvik and Apelsvoll had automatic irrigation systems (Rainbird Inc.) and were irrigated after seeding/reseeding, fertilization, topdressing and otherwise at 10–15 mm soil water deficit. The trial at Korpa did not have an automatic irrigation system but was irrigated manually during establishment in August 2007, after reseeding in spring 2008 and otherwise when considered necessary. No pesticides or growth regulators were used in any of the trials, but the whole trial at Landvik was treated with the soil surfactant Revolution (Aquatrols Inc., Paulsboro, NJ, USA) at 20 L ha−1 on 3 June 2010. Verticutting was performed once or twice per season in the red fescues and perennial ryegrass and up to four times per season in the other species. Heavy topdressing of all grass species was performed after reseeding and otherwise up to three times per season at Korpa, six times per season at Apelsvoll and 16 times per season (almost weekly) at Landvik. Partly because of the longer growing season, the total amount of sand applied during the experimental period was 18 mm at Landvik as opposed to only 8 mm at Apelsvoll and even less at Korpa.
The experimental greens at Landvik and Apelsvoll were exposed to abrasive wear and compaction from a drum with golf spikes mounted on it. Treatments were sporadic at Apelsvoll in 2008 and 2009, but at least twice per week corresponding to approximately 20.000 rounds of golf per year at Apelsvoll in 2010 and at Landvik in all experimental years. No wear machine was available at Korpa.
Registrations, statistical calculations and presentation of results
The trials were rated at monthly intervals using common terminology for turfgrass variety testing (BSPB/STRI 2011, NTEP Citation2008). The characters were defined as follows:
| • | Visual merit (overall turfgrass quality, 1–9, 9 is best quality): At Landvik, the overall mean was weighed with 1/7 on the sowing year 2007 and 2/7 on each of the following years. Due to reseeding of all plots in spring 2009, the overall mean for Apelsvoll was weighed with 1/6 on 2007, 2/6 on 2008, 1/6 on 2009 and 2/6 on 2010. Due to late sowing with no registration of visual merit in the sowing year and to the high mowing in 2008, the overall mean for Korpa was weighed with 1/5 on 2008, and 2/5 on each of the subsequent years. | ||||
| • | Tiller density (1–9, 9 is highest tiller number per unit area): Values for Apelsvoll and Landvik were weighed between years in the same way as visual merit. After reseeding in spring 2008 and 2009 at Apelsvoll, observations of tiller density were suspended until plant coverage was complete in August. Because of the high mowing in 2008, values for Korpa were weighed with 1/2 on 2009 and 1/2 on 2010. | ||||
| • | Leaf fineness (texture, 1–9, 9 is finest leaves): At Apelsvoll and Landvik, observations were weighed with 1/3 on each of the green years 2008, 2009 and 2010, and at Korpa with 1/2 on 2009 and 1/2 on 2010. | ||||
| • | In-season colour (1–9, 9 is darkest green): At all three sites, in-season colour was weighed with 1/3 on each of the years 2008, 2009 and 2010. | ||||
| • | Winter colour (1–9, 1 is pale or brown, 9 is intensely green): Intensity of green colour outside the growing season. Ratings were weighed with 1/3 on each of the years 2008, 2009 and 2010 at all sites. | ||||
| • | Living turf cover: Per cent of plot area covered with living, undiseased turf of the sown species. At Apelsvoll and Landvik, values were weighed with 1/7 on the sowing year (starting when grow-in was complete) and 2/7 on each of the subsequent years. At Korpa, values were weighed with 1/3 on each of the years 2008, 2009 and 2010. | ||||
| • | In-season disease (per cent of plot area): The most important disease was Microdochium patch although at Landvik, there were also some cases of red thread (Laetisaria fuciformis). Values were weighed as per cent living turf cover. | ||||
| • | Winter damage (per cent of plot area): Includes both biotic and abiotic winter damage. Means of assessments in the spring of 2008, 2009 and 2010. | ||||
| • | Turf cover 3 weeks after sowing in 2007: Indicates establishment rate. The first assessment of plant coverage was undertaken 20, 19 and approximately 40 days after sowing at Apelsvoll, Landvik and Korpa, respectively. | ||||
| • | Daily height increment (mm): Calculated from height measurements with a prism (Check Signature Inc., Shoreview, MN, USA) on the first Monday in each month at Apelsvoll and Landvik in 2008, 2009 and 2010. (The green had been left uncut since Friday.) Not measured at Korpa. | ||||
| • | Mat thickness (mm): Measured by the end of the trial in October 2010 at Apelsvoll and Landvik. This character was not measured at Korpa as very little mat accumulated at this northernmost site. | ||||
| • | Moss (per cent of plot area): Assessed in October 2010 at Landvik. | ||||
In order to facilitate comparison not only within, but also between species, characters were recorded on the same scale for all species. All recordings were undertaken by experienced researchers and technicians but direct comparisons among the three sites are not valid as no attempt was made to standardize scales.
The experimental data were analysed using PROC ANOVA (SAS Institute Citation2002). Significant differences among species/varieties and significant site×species and site×variety interactions were identified. When significant differences occurred, least significant differences (LSD 5%) were calculated for direct comparisons between species or varieties. P-values between 5% and 15% were reported as ‘tendencies’. Mean values for species were presented separately for each experimental site and for each climatic zone (). Due to space limitations for this paper, presentation of variety results within each species (Tables ) were limited to one table for Landvik (southern zone) and one combined table for Apelsvoll and Korpa (northern zone). Separate results from Apeslvoll and Korpa have been published elsewhere (Aamlid et al. Citation2011). Species or varieties were always ranked for visual merit scores. In cases where two or more species (varieties) had the same scores, they were further ranked for winter damage, in-season diseases and tiller density.
Results and discussion
Comparison of species ()
The interaction between species and experimental sites was significant for all characters recorded in the project. Chewings fescue and slender creeping red fescue were ranked significantly before creeping bentgrass, colonial bentgrass, rough bluegrass and perennial ryegrass at Apelsvoll and Korpa. Major reasons for this difference were fewer in-season diseases, primarily Microdochium patch, at Apelsvoll, and better winter survival at both sites. While the winter damage at Korpa and Apelsvoll was mostly abiotic, the red fescues also showed better resistance to pink snow mould which was the major reason for winter damage at Landvik.
Table III. Comparison of species.
Among the two subspecies of red fescue, chewings fescue had a darker in-season colour, and a less attractive, brownish winter colour, but it was more winter hardy and showed better spring performance than slender creeping red fescue. Virtually no invasion of annual bluegrass was observed at any of the three trial sites. In Danish greens trials, Nielsen (Citation2010) found slender creeping red fescue to be more competitive than chewings fescue to annual bluegrass, and he suggested at least 60% of this subspecies in red fescue seed blends for golf greens (N.C. Nielsen, pers. comm. Dec. 2010). In the northern climatic zone, the proportion of slender creeping red fescue should probably be lower since it is less winter hardy than chewings fescue.
Although not as fast as perennial ryegrass, the red fescues, in particular chewings fescue, had faster height growth than the bentgrasses. Because of lower tiller density and more erect leaves in red fescues, this does not imply that turfgrass ball roll is slower or that mowing frequency would have to be higher on red fescues than on bentgrass greens. In a parallel project at Landvik where fertilizer rates were differentiated in a similar way to that in our trials, Ericsson et al. (Citation2012b) found that clipping yields decreased in the order creeping bentgrass > colonial bentgrass > chewings fescue > slender creeping red fescue > velvet bentgrass.
Despite more winter damage from snow mould, creeping bentgrass was ranked significantly before the red fescues at Landvik. In most cases, the snow mould only affected bentgrass leaves, and the turf recovered quickly from tiller apices. Unlike in our previous trial (Aamlid and Molteberg Citation2011), creeping bentgrass was not infected by take-all patch (Gaeumannomyces graminis), and it was more resistant than colonial and velvet bentgrass to Microdochium patch and red thread. Another explanation for better performance of creeping bentgrass than of red fescue at Landvik could be the twofold difference in fertilizer levels; 1.6 kg N 100 m−2 yr−1 to creeping bent grass vs. 0.8 kg N 100 m−2 yr−1 to red fescue. Being located in an area with a long growing season and high rainfall, fertilization of red fescue plots was apparently too low, thus allowing invasion of mosses on the green surface at Landvik. It is noteworthy that red fescue performed relatively better compared with the bentgrass species under the higher fertilizer regime at Korpa. Ericsson et al. (2012a, 2012b) found that the nitrogen requirement for maximal growth of red fescue was only half of that in creeping bentgrass, but when practiced in the trial at Landvik, this resulted in a nitrogen rate that was too low for optimal performance of red fescue. This interpretation is substantiated by Nielsen (Citation2010) who found Danish red fescue greens to require 0.9–1.2 kg N 100 m−2 yr−1 for optimal performance.
In the Nordic countries, red fescue has commonly been seeded in mixtures with 10–20% colonial bentgrass for improved tiller density and autumn colour. Colonial bentgrass was, however, a disappointment as it was susceptible to in-season diseases in both climatic zones and invaded by mosses to the same extent as red fescues at Landvik. Poor performance of colonial bentgrass was reported also in a Danish project where it was less wear tolerant and less competitive than red fescue to annual bluegrass (Nielsen Citation2010). Part of the reason for the poor performance of colonial bentgrass in our trials may be that it received the same amount of fertilizer as red fescue, which is lower than the intermediate requirement (relative figures 50 for red fescue, 71 for colonial and velvet bentgrass, and 100 for creeping bentgrass) predicted by Ericsson et al. (Citation2012a, Citation2012b). That colonial bentgrass requires more nitrogen than red fescue is substantiated by better performance in our previous project where it received the same amount of fertilizer as creeping bentgrass (Aamlid and Molteberg Citation2011) and by Danish results showing seed mixtures of red fescue and colonial bentgrass to have an advantage over pure seed blends of red fescue only if the annual fertilizer rate was 1.5 kg N 100 m−2 yr−1 or higher (Nielsen Citation2010). German green trials with an annual input of 2.0 kg N 100 m−2 yr−1 showed more wear tolerance and better winter hardiness of mixtures with 80% red fescue and 20% colonial bentgrass than of pure red fescue (Wolleswinkel et al. Citation2010).
Although less superior than in our previous project (Aamlid and Molteberg Citation2011) and in British variety trials (BSPB/STRI 2011), velvet bentgrass performed significantly better than any other species at Landvik. In spite of receiving 50% less fertilizer, velvet bentgrass had significantly higher tiller density and better winter survival than creeping bentgrass in both climatic zones. Velvet bentgrass also had finer leaves, better winter colour and less height growth than the other bentgrass species. However, on the negative side, it accumulated a thicker mat layer than the other species, and it was also susceptible to in-season diseases and to pink snow mould. These results are in agreement with the conclusion that velvet bentgrass is an alternative not for golf courses aiming for less fungicide use, but for courses demanding extraordinary playing quality and having sufficient resources for thatch control (Tronsmo et al. Citation2008, Espevig et al. Citation2011, Citation2012).
Perennial ryegrass and rough bluegrass were included in this project mainly because some greenkeepers use them to quickly reestablish turf on dead greens in spring. If such use is at all warranted, our results suggest that rough bluegrass is just as fast in establishment as perennial ryegrass. Rough bluegrass also had less height growth, higher tiller density, finer leaves and darker colour than perennial ryegrass. However, as the varieties of rough bluegrass were primarily developed for overseeding of bermudagrass greens in the southern United States (e.g. Seed Research of Oregon Citation2011) they were not adapted to the light and temperature conditions at high latitudes. Rough bluegrass plots sometimes had a peculiar green appearance in the middle of the winter, and at Landvik they were totally invaded by bentgrasses from neighbour plots. Such a low persistency may perhaps be considered an advantage for a species primarily intended as a nurse crop for other turfgrass species, and rough bluegrass has indeed found a certain use in mixtures for reseeding of winter-damaged golf greens in northern Sweden (Hedlund Citation2006, B. Sandström, pers. comm. 2011). By contrast, perennial ryegrass showed surprisingly high persistence at 5 mm mowing height. Perennial ryegrass may perhaps, in the initial phase, prevent annual bluegrass from establishing from the soil seed bank, but in the long run, the presence of a certain number of perennial ryegrass plants that require frequent mowing and have low tiller densities are hardly helpful in reducing the requirement for pesticides, mowing or other input factors on Nordic golf greens.
Chewings fescue varieties ()
At Landvik and on average for Apelsvoll and Korpa, ‘Musica’ had significantly higher tiller density than any other variety of chewings fescue. At Landvik, ‘Musica’ was also in a class of its own with regard to visual merit score. These results are in good agreement with BSPB/STRI (2011) which ranked ‘Musica’ before other chewings fescue varieties at 4–7 mm mowing height. Poor winter colour is usually a disadvantage of chewings fescue in winter-mild areas, but in that regard, ‘Musica’ represented a significant improvement compared with the other varieties in the project. ‘Musica’ was, however, equally susceptible to pink snow mould, Microdochium patch and red thread as the other varieties of chewings fescue.
Table IV. Chewings fescue varieties.
Besides ‘Musica’, improved varieties of chewings fescue that had sufficient density to prevent invasion moss and other weeds ‘Barswing’ and ‘Greensleeves’ in the southern zone and ‘Greensleeves’ and ‘Charme’ in the northern zone. These varieties were also highly ranked by BSPB/STRI (2011). Norwegian and Swedish breeding lines (designated LøRc and SW RS, respectively) showed no improvement in winter hardiness compared with varieties of more southern origin, but ‘LøRc 0215’ was, nevertheless, among the best varieties in the northern zone.
Slender creeping red fescue varieties ()
The control variety ‘Cezanne’ obtained low scores for turf establishment at all sites. This probably reflects poor quality of the seed lot. ‘Cezanne’ was, nonetheless, ranked among the best varieties in the northern zone, but differences were not significant. The test varieties ‘Viktorka’ and ‘Finesto’ were dense enough to totally exclude moss at Landvik, but none of them represented any improvement in winter hardiness or resistance to in-season diseases. At Landvik, they were almost significantly more affected by snow mould than ‘Cezanne’. Our data suggest that resistance to biotic and abiotic winter damages should be taken more into account when breeding new varieties of slender creeping red fescue.
Table V. Slender creeping red fescue varieties.
Colonial bentgrass varieties ()
Significant site×variety interactions indicated different ranking of colonial bentgrass varieties in the northern and southern zone. The Danish variety ‘Greenspeed’ and the British variety ‘AberRoyal’ were more susceptible to winter damage than the Norwegian varieties ‘Leirin’ and ‘LøEk 0015' in both zones, but due to finer leaves, higher density, better winter colour, and more competition against moss they were nevertheless ranked before the Norwegian varieties and the control variety ‘Jorvik’ in the southern zone. As in the previous test round (Aamlid and Molteberg Citation2011), ‘Jorvik’ represented a compromise between northern and southern adaptation and produced the highest visual merit score on average for Apelsvoll and Korpa. Because of the strong site×variety interaction in colonial bentgrass, the question of whether a pure blend of red fescue or a mixture of red fescue and colonial bentgrass is preferable for IPM management of Nordic golf greens depends, to a large extent, on the availability of seed of climatically adapted varieties of colonial bentgrass.
Table VI. Colonial bentgrass varieties.
Creeping bentgrass varieties ()
On average for two sites, the control variety ‘Independence’ was surpassed only by ‘CY-2’ in the northern zone. ‘CY-2’ showed particularly good performance at Korpa and was also among the mostly highly ranked varieties at Apelsvoll. The quality of ‘CY-2’ on putting greens is in good agreement with NTEP (Citation2008) giving it the highest rank on average for 11 trials in North America.
Table VII. Creeping bentgrass varieties.
In the northern zone, ‘Declaration’ performed poorly, especially at Apelsvoll, but in the southern zone it was ranked on top because of higher tiller density, more freshly green winter colour and better resistance to snow mould than ‘Independence’. Internationally, the greatest advantage of ‘Declaration’ is its high resistance to dollar spot (Sclerotinia homeocarpa, NTEP Citation2008), a disease which, so far, has not been a problem in the Nordic countries. Next to ‘Independence’ but with snow mould damage at Landvik, was ‘Runner’ which was also ranked shortly behind ‘Independence’ by STRI/BSPB (Citation2011). Among older varieties with lower tiller density, ‘L-93’ performed reasonably well in the northern zone.
Velvet bentgrass varieties ()
Differences in visual merit among the three velvet bentgrass varieties were not significant in either zone. ‘Villa’ was, however, less influenced by in-season diseases and therefore ranked slightly before ‘Vesper’ and ‘Legendary’. STRI/BSPB (Citation2011) ranked velvet bentgrass cultivars in the order ‘Vesper’=(9.3) > ‘Villa’ (8.7), but our results are in better agreement with the NTEP (Citation2008) which reported the following visual merit scores: ‘Villa’ (5.3 ) > Legendary (5.2)=‘Greenwich’ (5.2)=‘Venus’ (5.2) > ‘Vesper’ (5.0) > ‘Avalon’ (4.9) (NTEP Citation2008). For an already extremely dense species such as velvet bentgrass, increases in tiller density beyond that of ‘Villa’ can hardly be regarded as an improvement.
Table VIII. Velvet bentgrass varieties.
Perennial ryegrass varieties (Table IX)
‘Chardin’ was ranked significantly before the other perennial ryegrass varieties in both climatic zones. In the southern zone it also had finer leaves and was significantly denser resulting in less invasion of moss. All perennial ryegrass varieties had similar winter survival except for ‘Madrid’ which was significantly more susceptible to snow mould at Landvik
Table IX. Perennial ryegrass varieties.
Rough bluegrass varieties ()
Although ‘Quasar’ was ranked significantly before ‘Race Horse’ at Landvik, differences between the two varieties were generally small in both climatic zones.
Table X. Rough bluegrass varieties.
Conclusion
These trials, managed without pesticides, suggest that several species and species combinations are useful for IPM of golf greens in the Nordic countries. Fewer alternatives are available if pesticides are totally banned from golf courses. The red fescues had significantly better disease resistance and overall winter hardiness than the bentgrasses, and with a total ban on pesticide use, our recommendation for the northern zone will be a pure seed blend of at least two good varieties of chewings fescue (60–70% by weight) and one or preferably two good varieties of slender creeping red fescue (30–40% by weight). With no fungicides, a seed blend of red fescue, but with a higher proportion of the slender creeping type (e.g. 50% chewings fescue + 50% slender creeping red fescue), should be the first option even in the southern zone. Admittedly, a disadvantage of red fescue was lower tiller density and thus less competition to mosses than in the bentgrasses, but this can probably be resolved by selecting the best varieties and applying more nitrogen to immature greens. Invasion of annual bluegrass is another problem commonly encountered on red fescue greens, but again, the use of high-density cultivars such an chewings fescue ‘Musica’ or slender creeping red fescue ‘Viktorka’ may be helpful along with a restrictive irrigation programme.
The present use of fungicides on Nordic golf courses is already very low, usually one or two applications per year. If this practice can be continued as part of an IPM strategy, colonial bentgrass may be mixed into the red fescue at a weight ratio of 5–10%. Since colonial bentgrass varieties are often strongly adapted to climate, it is even more important for colonial bentgrass than for the other species to use different varieties in the northern and southern zone. We also consider creeping bentgrass and velvet bentgrass as compatible with IPM management of golf greens; creeping bentgrass primarily on courses in the southern zone and velvet bentgrass only on courses that have experienced greenkeepers and resources for thatch control.
For repair after winter damage, our primary recommendation is to use an ordinary seed blend or mixture consisting of durable species. Should there be a need for extraordinarily fast repair, e.g. before a tournament, the combination of fast establishment and high tillers density, but low persistency resulting from lack of adaptation to Nordic climate conditions, makes rough bluegrass more suited as a temporary nurse crop than perennial ryegrass.
Acknowledgements
This research was funded by the Scandinavian Turfgrass and Environment Research Foundation (STERF) and variety entrance fees paid by the plant breeders/seed companies.
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