Supina bluegrass: a new turf species for the North
Maintaining quality turf stands that withstand athletic-field conditions has always been a challenge, particularly in cool-season climates. Athletic-turf managers in warm-season climates typically use bermudagrass because of its high recuperative potential and exceptional stability. Unfortunately, a turfgrass with such qualities has not been available for cool-season turf managers.
Kentucky bluegrass (Poa pratensis) and perennial ryegrass (Lolium perenne)-the most commonly used turfgrasses for athletic fields in cool-season regions of the United States-provide good wear tolerance, but heavy traffic will wear the turf to bare ground, and these grasses' rate of recuperation is limited.
In Germany and other areas of Europe, supina bluegrass (Poa supina) has been used for many years on athletic fields because of its competitiveness, exceptional wear tolerance and disease resistance. Unlike other cool-season turfgrasses used for athletic fields, supina bluegrass is stoloniferous.
Research conducted in Germany suggests that supina bluegrass seeded at less than 10 percent of a mix with other cool-season turfgrasses will dominate the stand after several years of heavy traffic. The aggressive recovery from heavy traffic via their stoloniferous growth provides superior turf cover compared with stands that don't have supina bluegrass.
Though supina bluegrass seed is expensive (about $25 per pound), it usually constitutes less than 10 percent of a typical mix.
Studying Poa supina in athletic turf Much of our knowledge about the performance of supina bluegrass is anecdotal or based on research conducted in other countries. Thus, the need for research on this species is great. To better understand how supina performs on athletic fields in the United States, we initiated a series of studies at Michigan State University in 1996. Our study evaluated 'Supranova' supina bluegrass performance in Michigan. We looked at fertilizer requirements, mowing height, shade tolerance and competitiveness with 'Touchdown' Kentucky bluegrass in a seeding mix for athletic-field conditions. A primary objective was to determine the optimal seeding ratio.
To determine changes in stand composition over time with different seeding mixes, we planted six different seeding ratios (0, 5, 10, 25, 50 and 100 percent supina bluegrass). We grew the turf on a sand-based root zone (80:10:10, sand:soil:peat) beginning in June 1995 and fertilized with two levels of nitrogen (4 and 6 pounds per 1,000 square feet per year). Fertilizer regimes began during the 1996 growing season and continued through 1999.
We used a Brinkman Traffic Simulator (BTS) to simulate traffic on some plots, while others remained free of traffic to provide a comparison. We applied the simulated traffic in the fall of each year (1996 through 1999) in a manner intended to simulate wear typical of a National Football League field between the 40-yard lines and hash marks. We applied the equivalent of about 25 games per season. We then conducted plant counts in the spring of 1997 through 1999 to determine the change in composition (percent of each species present) following fertilizer and traffic treatments.
Results and conclusions After only one season of simulated football traffic, the proportion of supina bluegrass significantly increased (see graph, page Contractor 6). Three years of simulated football traffic increased the proportion of supina bluegrass in the stand to where it became the predominant species for most of the initial seeding ratios.
As long as some Kentucky bluegrass was present in the turf-even just 5 percent-no significant differences existed in turf shear strength (stability) compared with a 100 percent Kentucky bluegrass stand. Supina bluegrass alone provides somewhat less stability than Kentucky bluegrass or perennial ryegrass in sand-based fields. This is because supina bluegrass lacks the rhizomes of Kentucky bluegrass and the deep rooting of perennial ryegrass which increase their stability. However, when the ultimate goal is to maintain a uniform playing surface, the combination of supina bluegrass with other cool-season species provides good cover and recuperability as well as adequate stability. Even if the initial seeding of supina bluegrass consists of only 5 to 10 percent of a mix, it's likely the supina will become the dominant species in the most heavily trafficked areas.
Because supina bluegrass is a true cool-season turfgrass, it continues to grow late into the fall when other turf species have stopped growing. This ability to continue late-fall growth makes supina bluegrass a desirable turf species for athletic fields, especially for fall sports like football.
The aggressive growth of supina bluegrass makes it a desirable turf species for heavily trafficked situations. When the goal is to maintain high quality turf that can tolerate athletic field conditions, turf managers need every advantage they can get. Supina bluegrass provides recuperability not possible with traditional Kentucky bluegrass and perennial ryegrass athletic fields.
Other uses of supina bluegrass Investigators at Michigan State University have been researching uses for supina bluegrass in golf courses, athletic fields and home lawns since 1993. Some of the benefits of supina bluegrass are that it tolerates, and even thrives, over a wide range of cutting heights (0.5 to 2.5 inches) and that it has exceptional shade tolerance. In Germany, some golf courses use supina bluegrass on putting greens mown at 0.25 inch. These putting greens use supina bluegrass where the green is too shady to sustain an adequate creeping bentgrass stand. This is consistent with research findings from Michigan State that show exceptional shade tolerance for supina bluegrass. In addition, research investigating the turfgrass species for indoor athletic stadiums determined supina bluegrass was the superior turfgrass. Of course, this shade adaptability also is useful for shaded areas of home lawns.
Supina bluegrass is native to the mountain regions of central Europe where its tolerates and continues to grow under adverse (cold) growing conditions. It is usually the last turfgrass to go into fall dormancy and the first to begin actively growing in the spring.
In Michigan, the only turfgrass disease problem we've seen with supina bluegrass is pink snow mold. However, by the time other cool-season turf species have begun active growth in the spring, the supina bluegrass has already outgrown the effects of the disease.
The future of supina In addition to the research we are conducting at Michigan State, supina bluegrass is being studied in Germany as well as at several universities in the United States. Dr. John Stier at the University of Wisconsin-Madison has been looking into supina bluegrass's aggressiveness in mixes with tall fescue, perennial ryegrass and Kentucky bluegrass for athletic fields, and its competitiveness with annual bluegrass in golf course fairways. Studies of its cold and herbicide tolerance also are underway. Thus, our level of knowledge of this species should increase significantly during the next several years.
Currently, two commercial varieties of supina bluegrass are available-'Supra' and 'Supranova'. Both of these varieties were developed by Saatzucht Steinach in Germany. Philipp Berner (of Saatzucht Steinach) breeds supina in Germany, and a third variety of his will be released in the near future. In the United States, Poa supina seed is available through Ultra Turf Inc. (Lake Oswego, Ore.).
With the great potential of supina bluegrass in North America, U.S. breeders are now working with this species to develop even more varieties. The future of supina bluegrass appears promising, and its use as turf, whether for golf courses, athletic fields or home lawns, will surely increase.
John Sorochan is a turf research associate, and Dr. John N. Rogers III is professor of turfgrass science, both at Michigan State University (East Lansing, Mich.).
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