80 RASEN · TURF · GAZON 4/2024 ment, and uncertainties about winter hardiness, explain why tall fescue has not been used in seed mixtures for fairways up to recently. This is now changing as European plant breeders have started to develop fairway seed mixtures with tall fescue as the predominant grass species. There are also recent results from North America showing new tall fescue varieties to tolerate mowing down to 15 mm, i.e. 5 mm lower than in this experiment (L. Brilman, DLF-USA, personal communication). All in all, we think that tall fescue warrants further testing in seed mixtures for golf courses even in southern part of the Nordic countries, especially for semi-rough, but also for fairways with no or limited access to irrigation. Within perennial ryegrass, it was a new experience for us that tetraploid varieties had better drought tolerance and recovered faster from drought than diploid varieties. Apparently, the drought triggered many of the diploid varieties to form seed stalks which resulted in poor mowing quality and uneven plots. In contrast, tetraploid varieties have double chromosome numbers which normally imply lower tiller density, but more vigorous growth and perhaps better root development than diploid varieties. However, we also documented significant differences among the diploids, with ‘Slugger’ og ‘Zoom 2’ as two of the most drought sensitive and the old variety ‘Bargold’ as one of the more drought tolerant varieties. Creeping bentgrass developed, as expected, a rather fluffy surface at 20 mm mowing height, but coverage was less affected by drought than in most of the other species. Creeping bentgrass also showed the fastest recovery of all species when resuming irrigation after the drought period. In other words, while it is often argued that maintenance of creeping bentgrass fairways require extra resources to fertilizer, topdressing and mechanical thatch control, this argument is not valid when comparing irrigation requirement on fairways mowed at 20 mm. However, it remains to be tested if this holds true even for creeping bentgrass fairways mowed at 8 – 10 mm. Within colonial bentgrass, the Norwegian variety ‘Leirin’ had coarse leaves and low density, while the American variety ‘Heritage’ resembled creeping bentgrass, although with a less fluffy appearance. Our results confirmed earlier American results showing colonial bentgrass to be less drought-tolerant than creeping bentgrass, but that recovery after drought is similar in the two species (DaCosta & Huang, 2006). Of Kentucky bluegrass, two supposedly drought tolerant American varieties were entered in addition to the highly ranked European variety ‘Limousine’. ‘Prafin’ showed better color retention under drought than ‘Limousine’, but characters such as tiller density, leaf fineness and competitive ability against weeds were superior in the European variety. Across the three varieties, the drought tolerance and recovery ability of Kentucky bluegrass was intermediate compared with the other species. Perhaps the greatest disappointment in this experiment were the three subspecies of red fescue. Most turfgrass textbooks consider red fescue as one of our most drought tolerant turfgrasses, but in our experiment, most red fescue varieties lost their green color after 3 – 4 weeks of drought. In particular, that was the case for chewings fescue which also had the slowest recovery after drought. Because of higher tiller density and less weed encroachment, Chewings fescue was, nonetheless, ranked higher than strong creeping red fescue for turfgrass quality. The most drought tolerant subspecies of red fescue was slender creeping red fescue, in particular variety ‘Seroa’. A possible measure to avoid fine fescue dominated fairways from wilting during dry periods could be to replace some of the red fescue seed with seed of hard fescue or sheep fescue. In this experiment, sheep fescue had better color retention and was all-in all, more drought tolerance than hard fescue, but recovery after drought was poor in both species. A relevant question is to what extent hard fescue or sheep fescue can replace other species in fairway seed mixtures without compromising wear tolerance on golf courses with a high number of played rounds per year. Concluding remarks It is too early to draw conclusions as this experiment will continue with new drought and recovery periods in 2025. However, the first-year data presented may perhaps inspire turfgrass managers to rethink what is meant by a ‘drought tolerant turfgrass species’. In FAIRWATER we define this as a species which, at 20 mm mowing height, retains high coverage and high visual quality during prolonged drought periods. Other quality parameters such as high tiller density, fine leaves, low clipping yields, low requirements for pesticides and fertilizers, and to what extent the turfgrass stand carries the ball, may perhaps be equally important. For many years, these characters have been important arguments for the choice of red fescue as the primary component in seed mixtures for fairways in the Nordic countries. While most greenkeepers are likely to acknowledge that red fescue dominated fairways turn yellow or ‘golden’ during drought periods, it may perhaps be harder to accept that red fescue, and especially Chewings fescue, are among the slowest to recover once rainfall or irrigation resumes. Regardless of that, most golfers will probably prefer to play on fine-leaved, yellow-to-brown red fescue fairways as compared with green, but coarse-leaved fairways dominated by tall fescue. Yet, the question remains what will happen if the drought period becomes so long and severe that the red fescue does not recover but leaves open spaces for annual bluegrass encroachment once water again becomes available? Rather than drastic changes, we recommend greenkeepers to discuss species compositions and perhaps establish small demos with seed mixture that include tall fescue and/or tetraploid perennial ryegrass on their most drought sensitive fairways. It must also be clarified to what extent the tall fescue varieties currently available in Europe will tolerate a reduction in mowing height from 20 to 15 mm. Reference DaCosta, M. & B. Huang, 2006. Minimum water requirements for creeping, colonial and velvet bentgrass under fairway conditions. Crop Science 46: 81-89. Autor: Trygve S. Aamlid Anne F. Borchert Karin J. Hesselsøe Iris Eik Trond Pettersen Paula Lawicka NIBIO Turfgrass Research Group. Reddalsveien 215 N-4886 Grimstad E-Mail: trygve.aamlid@nibio.no
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