Managing the New Alpha-Bents
A group of new creeping bentgrass varieties released several years ago have earned the collective nickname “A and G series.” These grasses were selected by turfgrass breeder Dr. Joe Duich, Pennsylvania State University, from old Penncross putting greens in Georgia. They include A-1, A-2, A-4, G-1, G-2 and G-6. Their shoot density is 25 percent greater than Penncross, which may better allow them to resist invasion by annual bluegrass (Poa annua). As a group, they typically rank at or near the top of the National Turfgrass Evaluation Program (NTEP) trials due to their fine leaf texture, uniform surfaces and high quality. Some users boast of their disease-resistance, which could reduce fungicide applications.
Duich recommends a low mowing height, about 0.125 to 0.156 inch, and has said they require more frequent topdressing and cultivation than cultivars like Penncross in order to avoid problems with excessive thatch development. Consequently, many turf managers have been afraid to adopt the A and G cultivars because they want to avoid additional management costs. Another concern turf managers have is that the sheer density of the grasses might prevent topdressing from working its way down through the canopy, causing an excessive amount of the coarse sand particles to be picked up. The result would be a layer of fine-textured sand that might interfere with water infiltration.
DETERMINING THE TRUE MANAGEMENT REQUIREMENTS OF THE A AND G SERIES BENTGRASSES
We set out to determine the extent of additional topdressing and cultivation requirements for managing A-4 and G-2 compared to Penncross. Plots of A-4, G-2 and Penncross were seeded at the O.J. Noer Turfgrass Research and Educational Facility in Wisconsin during autumn 1998. We mowed the turf six days each week at a height of 0.125 inch and removed the clippings. Turf was fertilized four times yearly with about 1 pound nitrogen (N) per thousand square feet with each application. In spring 1999, we began topdressing the turf on either a monthly or biweekly interval, with and without verticutting before topdressing. We used an 80:20 sand:peat topdressing mix and applied a total of 0.031 inch depth each month, equal to about 110 pounds per thousand square feet. The topdressing mix met USGA requirements, so the majority of the sand particles were of medium size, with much smaller fractions of coarse and fine materials. We brushed the topdressing into the turf then irrigated to replace the estimated daily water loss (ET). Coring (core aeration) was stripped across all plots to compare the effects of monthly versus a single annual core aeration in the fall. We used 0.25-inch-diameter tines for the monthly coring and 0.5-inch-diameter tines for all the plots for the final or single fall aeration. We removed the cores, and the monthly topdressing treatment always followed coring. Most golf courses are reluctant to use core aeration more than once in the fall or spring because of the time required for the turf to recover from the damage. Core aeration is a proven method to reduce thatch production, and we needed to find out if aggressive coring made a difference in thatch production and loss of topdressing through mowing.
The day following topdressing, we separated the topdressing collected in the mower buckets from the leaf clippings. The topdressing was sieved to determine the sizes of particles picked up by the mower. Each month we rated the turf for color, quality and disease. When disease occurred we allowed it to progress to a point where we could “rescue” the turf with a fungicide before rating disease severity. Once each fall in 2000 and 2001, we collected cores from each plot to measure thatch depth and weight.
As expected, both A-4 and G-2 had significantly better turf quality than Penncross throughout the year. On a one to nine scale, with nine equal to perfect turf and six considered acceptable for a putting green, both A-4 and G-2 rated a seven to eight throughout the growing season. Their turf quality was acceptable by May, while Penncross didn't have acceptable turf quality until June in 2000 and July in 2001. The color of G-2 was a noticeably lighter green than either A-4 or Penncross, but was not unacceptable. Both A-4 and G-2 had noticeably better turf density, which helped to prevent weeds such as Poa annua. The overall uniformity of A-4 and G-2 was significantly better than Penncross, which tends to form patches of different colors and textures over time. Penncross had significantly less dollar spot than either A-4 or G-2, with an average of 19 spots per 1,000 square feet versus 40 spots in G-2 and 150 spots per 1,000 square feet in A-4 turf. The difference in dollar spot occurrence could be due to the lower turf density of Penncross, which makes it more difficult for the dollar spot fungus to spread leaf to leaf. The large difference between dollar spot disease in G-2 and A-4, however, indicates G-2 simply may have better disease resistance, as turf density was about the same.
TOPDRESSING LOSSES BY MOWING
Surprisingly little topdressing sand was removed by mowing. A-4 had the most topdressing removed at 2.8 percent, while G-2 and Penncross both had only about 1.8 percent of the topdressing removed. The size of sand removed was fairly equally spaced among the coarse, medium and fine particle sizes. Given the relative uniformity of loss between particle sizes and the small amount of total topdressing lost, there is no reason to believe that A-4 or G-2 will cause a layer of finely-sized sand particles to develop and inhibit drainage in a putting green.
Topdressing frequency and the use of verticutting affected topdressing losses only by a small amount. Topdressing monthly resulted in the loss of 2.3 percent of the topdressing applied, compared to losses of 2.0 percent for biweekly topdressing and 1.7 percent for biweekly topdressing following verticutting. Although the combination of verticutting and applying topdressing at two-week intervals caused the least amount of topdressing to be lost, the temporary disruption to the putting green surface caused by verticutting may not be worth the price of retaining an extra 0.6 percent of topdressing.
Coring monthly had the opposite effect than was intended. Monthly coring resulted in 2.1 percent of the topdressing being picked up by mowing, while only 1.8 percent of the topdressing was removed in plots cored once a year. As it turns out, monthly coring brought more sand to the surface for mowers to pick up than it allowed to fall into the putting green profile.
Both A-4 and G-2 produced significantly more thatch than Penncross (see Table 1, above). By 2000, A-4 and G-2 both had about 0.6 inch of organic matter at the surface compared to 0.5 inch for Penncross. In 2001, both A-4 and G-2 had about 1 inch of organic matter compared to 0.6 inch for Penncross. However, the turf surfaces did not feel any more “puffy” than the Penncross surfaces due to the dilution of the thatch with the topdressing. In other words, all of the topdressing and cultivation combinations effectively diluted the thatch to produce a “mat” layer. Although high in organic material, with individual roots and stolons still often visible, a mat layer is acceptable as its firmness allows mowing without scalping and provides a firm playing surface compared to undiluted thatch.
None of the cultivation methods significantly affected the thatch layer. Although topdressing biweekly may have allowed a slightly greater amount of topdressing to enter into the turf to dilute the thatch layer, the extra labor and equipment wear and tear is probably not worth the cost. Thus, monthly topdressing with one annual core aeration will generally be acceptable for managing A and G series bentgrasses. Avoid going too long between topdressing because a sandwich-like layer of thatch and mat layer can develop, which will prevent good drainage.
NO EXTRA EFFORT
A-4 and G-2 require about the same amount of topdressing and coring efforts that are required for management of Penncross greens. Biweekly topdressing and verticutting, combined with monthly coring, can slightly decrease the amount of topdressing lost by mowing, but because no more than 3 percent of topdressing is removed even from the dense turf of A-4, the overall effect is minor. Both A-4 and G-2 have far better turf quality than Penncross. A-4 is more susceptible to dollar spot disease than either G-2 or Penncross. Of the three cultivars, G-2 should provide the best combination of turf quality, dollar spot resistance and management requirements.
Dr. John Stier is associate professor of environmental turfgrass science at the University of Wisconsin (Madison, Wis.).
|Depth of thatch (inches)||Weight of thatch (oz / in
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