When alternatives to the long-used stalwart Penncross creeping bentgrass began to emerge, they quickly became known for their improved quality. The Penn State varieties (Penn A-4 and Penn G-2 among them) were noteworthy for having upright growth, high shoot density and narrow leaves. In some quarters, it was thought that aggressive and upright growth could lead to more thatch, resulting in more rigorous thatch management and more frequent topdressing and aeration.
By the late 1990s, there was a lot of chatter about thatch, but not much research to determine whether the concerns were valid. So, in 1998, John Stier, Ph.D., who was then at the University of Wisconsin, set out to determine whether the chatter was true. Did the newer (for that time) Penn varieties really need more cultivation and topdressing sand? And, given the higher shoot density of the new cultivars, were there issues with incorporating the sand?
In 1998, new plots of Penncross, Penn A-4 and Penn G-2 were seeded on a sand-based (USGA-recommended) root zone. A recently released variety of a Poa annua var. reptans (called, at the time, DW-184) was also included as a seeded treatment. All the varieties were allowed to establish until spring 1999, when the greens reached a final mowing height of 0.125 inch (3.2 mm).
In May 1999, the aeration and topdressing treatments were started. They consisted of: (1) topdressing (no verticutting) monthly or every two weeks, or topdressing every two weeks following verticutting; and (2) core aeration (with cores removed and topdressing applied) either once (October) or four times (May, July, September and October). The October aeration used tines that were 0.5 inch (1.3 cm) in diameter, and the other applications used tines that were 0.25 inch (0.6 cm) in diameter.
Cultivation was performed through 2001, and data on thatch depth and thatch mass (collected by combusting the samples to eliminate the effect of sand) was collected. The amount of topdressing sand collected in clippings was also determined, with the sand separated from clippings collected one day after topdressing application. Additional data included plot quality, color and disease severity.
Not surprisingly, the newer varieties of Penn A-4 and Penn G-2 had more thatch and thatch mass than Penncross and the Poa annua. However, neither aeration frequency (once or four times) nor topdressing method affected the thatch of any of the cultivars. Although there were some differences in removal of topdressing sand via mowing (for example, combining the topdressing with vertical mowing reduced mower pickup), the overall loss of sand was small.
Anytime topdressing was applied, the overall loss of sand in clippings was only 1% to 3% of the amount applied, and, in general, the variety had no effect on sand loss. Finally, turf quality was most affected by variety, not cultivation. In this study, Penn A-4 and Penn G-2 consistently had higher quality than Penncross or the P. annua cultivar. In general, the topdressing and aeration needs of Penn A-4 and Penn G-2 did not differ significantly from typical practices, and the quality of these grasses was not reduced by the topdressing or aerification treatments.
Source: Stier, J.C., and A.B. Hollman. 2003. Cultivation and topdressing requirements for thatch management in A and G bentgrasses and creeping bluegrass. HortScience 38:1227-1231.
Beth Guertal, Ph.D., is a professor in the Department of Crop, Soil and Environmental Sciences at Auburn University in Auburn, Ala., and president-elect of the Crop Science Society of America. She is a 20-year member of GCSAA.