In Ireland, creeping bentgrass has become the grass of choice for most new golf course developments or for renovation projects in recent years. Successful creeping bentgrass management can produce first-class golfing surfaces. But mismanagement, as with any grass type, can lead to poor surfaces that are frustrating to golfers. The decision to use creeping bentgrass, and which variety (cultivar) to choose, needs to be based on a detailed knowledge rather than blind hope.
Here, Art Bruneau, of North Carolina State University, and the STRI's Ian Clements, discuss the origins of the newer varieties, and hope to dispel some of the myths associated with their management.
Why creeping bentgrass?
Creeping bent became the most common turfgrass for American putting greens because the browntops and velvet bents did not perform as well. Browntops in the US are less tolerant of close mowing, and more susceptible to disease and cold weather. In addition, they are less tolerant of traffic, slower to recover from injury, and less competitive to annual meadow-grass.
Velvet bent, on the other hand, can withstand low cutting heights and produce a beautiful putting green but only where it is best adapted, which seems to be limited to certain parts of New England. Velvet produces more thatch than creeping, often requiring more frequent topdressing because of its severe thatching tendency. It is also slow to recover from disease and is fairly disease susceptible.
In the last US NTEP (National Turfgrass Evaluation Programme) bentgrass putting green trial, no browntops were entered and the velvets that were entered were the poorest performers.
The early years
The earliest improved bentgrasses were selections taken from old putting greens that had been originally seeded with 'South German' bentgrass or a seeded variety known as Seaside. Seaside was harvested from creeping bentgrass areas indigenous to the coast of Washington and Oregon. South German bent was a mixture of numerous velvet, colonial and creeping bent strains.
Over time, through natural selection, certain strains would dominate the Seaside or South German bent greens resulting in a very patchy, unsightly turf. It is in these old greens that breeders would select stolons from the best looking patches. The material would be further tested under varying conditions and management regimes. The better performers received names such as Cohansey, Arlington and Toronto and were vegetatively increased and released.
Even though they produced seed, the selections had to be vegetatively planted to ensure uniformity. This involved the broadcasting and frequent topdressing of stolons and was common until the 1960s.
The first improved seeded creeping bentgrass was developed by Burt Musser at Penn State University and released commercially in 1954 as Penncross. In the 1950s and 60s Penncross was the most desirable bentgrass to use on greens in the USA.
It was the first seeded variety to produce a fairly uniform, vigorous putting surface. Since seeding was less expensive than 'stolonising', Penncross remained the favourite green turf for over forty years, even though it had a grainy texture and required relatively aggressive maintenance (routine grooming, light verticutting and topdressing) to refine the surface.
The next generation
In the late 1970s, television, golf and club members' demand for tournament conditions (higher quality and faster greens) created a renewed interest in breeding. Penncross, that had performed so well for so many years, did not perform well with the gradual reduction in mowing height (from 4mm to 3mm). Loss of turf vigour, scalping, and increased disease activity were some of the drawbacks noted.
Considerable resource was invested in developing improved varieties that could withstand close mowing (heights of cut in the 1920s were 6.35mm and, by the 90s, 3mm), without spiking up and with improved wear, heat and disease tolerance.
Dr Skogley at the University of Rhode Island collected germplasm from creeping bents in New England, Canada and the Mid Atlantic region out of which he produced (in conjunction with Seed Research Inc.) the variety Providence (SR1019). Dr Milt Engelke at Texas A&M was successful at breeding the varieties Cato and Crenshaw that are tolerant to high temperature stress but susceptible to dollar spot disease. L-93 was developed at Lofts and Rutgers from germplasm collected in the 1980s from golf courses through New Jersey, New York, Pennsylvania and California. Southshore was also developed from the same programme.
The creeping bentgrass varieties, released in 1995, commonly referred to as the A and G series, were developed by Joe Duich at Penn State University out of selections from Augusta, Ga., greens originally sown with Penneagle and Penncross. These are varieties that are capable of producing extremely fine, uniformly dense turf (similar in appearance to velvet bent) and suited to very close (3mm) mowing.
It is now thirteen years since the A and G series were first released and, whilst breeding new varieties is a slow and laborious process, what of the future?
There are currently twenty creeping bent and six velvet bentgrasses in the 2003 NTEP trial in the USA. Some of the new varieties listed under various maintenance practices are showing promise, these include, in no particular order:
• CY-2 (Snow Brand Seed Co & Chiba-Prefecture Agr. Exp.Station)
• Declaration (Lebanon turf products
• 007 - DSB (R.H. Hurley, LLC/Seed Res. Oregon/Pickseed)
• Shark - 23R (Mountain View Seeds)
• Tyee - SRX 1GD (Seed Res. Oregon)
A new NTEP trial, sown in the autumn of 2008 will provide information on the performance of these and, no doubt, newer varieties for the next five years.
New creeping bentgrass characteristics and management
Shoot and root density - A high shoot and root density is desirable for putting green turf. Fine leaves and an erect growth habit help create smooth and true surfaces on which to play. It also reduces the rolling resistance of the golf ball as it travels across the surface. The new Penn A and G series provide shoot densities 50-70% denser than Southshore and Providence and 100-150% denser than Penncross.
They are comparable to the dense stands of Poa annua var. reptans, found in many old push-up greens, and appear similar to the finest velvet bentgrasses in density and texture. People often cite their high-density characteristics as a mechanism to prevent annual meadow-grass ingress. Does this happen? Well, in reality no, annual meadow-grass can still invade these surfaces, if injured or thinning occurs particularly during the dormant winter months. Annual meadow-grass invasion is determined very much by the levels of winter play.
A study at Ohio State University showed that newer varieties with high shoot density (A and G series) have more roots in the spring than earlier varieties. The higher root densities can aid in pest and stress tolerance. This may become more of a concern if hot, dry summers become more frequent.
Mowing, rolling and ball marks - Close mowing helps to retain grass density and these grasses thrive on a tight cutting regime. The optimum mowing heights are between 4mm and 3mm, however some of the newer varieties have been mowed as low as 2.5mm during tournament play. It is common for some courses to roll greens once or twice weekly to minimise the need to reduce the mowing height.
There has been concern that the newer cultivars are not as aggressive as Penncross and this is one reason why ball marks seem to be more evident on greens planted with the newer varieties.
However, studies have shown that these new varieties actually heal just as quickly if not sooner than Penncross. It is felt that this perceived problem was a result of comparing very young turf, having little mat for cushioning, to older Penncross that had developed a cushioning mat. It seems that the ball marks become less noticeable as the green ages, no matter which variety is chosen.
Topdressing - Topdressing with sand that is comparable to the green mix is the most effective means of preventing thatch accumulations. Weekly or bi-weekly applications are the norm in the US. The high shoot density of the newer varieties can lead to quick thatch production if managed incorrectly.
I had the pleasure of visiting Bayville Golf Club, Virginia in 1997, one of the first courses in the States to seed to Penn A4 in 1995. Cutler Robinson, the Superintendent there, explained the maintenance regime to me then.
Topdressings were applied to match growth rates and Cutler was aiming to apply 30-35 dressings over the year (weekly during the growing season). Surface preparation consisted of double cutting on 169 occasions and double rolling on 32 occasions. Greens were single cut on 93 occasions and rolled once on 157 occasions.
Clean and uniform sands integrated into the turf canopy help to reduce mower wear and damage. Mechanical brushing also helps sand integration, but care is required during summer drought stress as this can exacerbate leaf burn.
Aeration - A healthy growing environment is necessary for strong bentgrass growth and, whilst modern golf green constructions can assist, there is still a requirement to aerate frequently. In fact, smaller tines used regularly will offer agronomic benefits while not adversely affecting playability.
Coring with 6mm (often referred to as needle or pencil) tines may be required three to four times over the season and can be supplemented with less aggressive mechanisms such as HydroJecting or solid tining.
One thing is clear, invasive aeration treatments such as hollow coring should only be attempted during the growing season; outside this the holes are a potential gap for meadow-grass invasion.
Verticutting and grooming - Brushing and light grooming is preferred for the maintenance of sward texture and uniformity. Aggressive verticutting should be avoided as this weakens and thins the sward. It is common in the US for greens to be verticut at least once in the spring and again in the autumn.
Frequent grooming, with groomers, brushes or grooved rollers, is an excellent means of minimising excessive thatch while enhancing green speed, but take care! In any case, if topdressing is completed with sufficient frequency there should be little need for verticutting to remove thatch, as it has never been allowed to accumulate in the first instance. Well-diluted mat is always the aim of good turf husbandry.
Nutrition - There is insufficient room here to talk about bentgrass nutrition in depth but it is sufficient to say that, the more you apply, the more aggressive the maintenance regime has to be. One misconception about creeping bentgrasses is that they require high nitrogen inputs. Established Penn A4 greens can get by on as little as 150kg N/ha/yr. Good nutritional programmes, as practiced for the maintenance of any turf, will work although bentgrasses do thrive with ammonium sulphate as the main nitrogen source.
Costs - There is no doubt that the newest creeping bentgrass varieties are more costly to maintain than earlier varieties. Cutler Robinson at Bayville had estimated that his Penn A4 greens management was 16% higher than his previous experiences with Penncross.
Most of this was tied up in extra mowing, rolling and topdressing operations as his pesticide and fertiliser costs had actually reduced! The question should surely be, is it worth it?
The final choice - The philosophies of creeping bentgrass management don't change when new and improved cultivars are chosen. Successful management only comes about through an understanding of the dynamics of environmental conditions on turfgrass growth and a willingness to adapt to the needs of the turf.
An informed decision on cultivar selection should be made on the basis of all the facts available, including the financial constraints of the club. We would all like to own and drive a Lamborghini and might well be able to afford to buy one, but can we afford the running costs? Maybe it is better to have a good workhorse than a finicky thoroughbred.
At tournament sites with low mowing heights and the need to produce tournament conditions regularly, then the Penn A and G series might well be the preferred choice, more so if winter play is carefully controlled. On sites with medium to heavy play, moderate budgets and moderate mowing heights then varieties such as L-93, Providence and Southshore might be preferable.
If you are interested in reviewing the performance of the latest bentgrass variety trials in the USA, these can be seen at www.ntep.org. In the UK, this information is available in the BSPB/STRI publication Turfgrass Seed where ten creeping bentgrass cultivars are currently in trial.