Issue link: http://read.dmtmag.com/i/82830
Continued From Page 39 more efficient at extracting that nutrient. While phosphorus exists predominantely in the top 4 of soil, poas rootzone is most effective at this depth. In terms of phosphorus availability, and in contrast to bentgrass physiology, poas rootzone is ideally adapted at shallow depths. Subsequently, those resources are not wasted on deep rooting, but are allocated to tillering or seed production. The gradual evolution of diploid poas can be visible in just 10yrs. The 60+ year poas on older courses can have extremely high shoot densities, and occasionally super high densities 10X that of the tightest bent grasses. The aforementioned selection forces and close mowing over six decades result in the adaptation of the lowest tightest turfs in the world - that adaptation associated with close mowing. When we review the relative competitiveness of both bent and poa, and efforts to maintain bents over poa, we must realize poa has its competitive advantage in spring and fall during cooler weather. Where bentgrasses have higher fitness in the summer, the seed bank of poa remains ready to establish whenever bare areas in the stand occur and should therefore we should be most diligent in maintaining dense surfaces during poas periods of advantage. To further assess the best management strategies to compete with diploid poas, diploid plugs were cut into bent surfaces and proved that Pennlinks and Pencross were in fact less resistant to spread than A-4 or G series due to their aggressive growth 2010 US OPEN AT PEBBLE BEACH habits. However, having visited many courses over the years, there are many superintendents who still maintain poa free greens in these older bent varieties. Those that have managed traffic, winter kill and recuperation and ensured dense surfaces, have proven the greater advantage against encroaching poas. As a result, without germination of those annual biotypes, the diploid poas have no chance to evolve, having little or no opportunity to escape the seed bank. Applying minimum nitrogen rates around 2.1lbs per year on older Pencross bents also provide an advantage over the early stage poas. When considering interseeding of A's and G's and convert old to new, we must also realize that equivalent opportunity for the poas can germinate. Although reviews are mixed, the recurring statements 'high rates and diligence' are most common. For those wanting to favor the diploid adaptation and promote poa greens, once the surface is primarily poa beyond their tenth year, minimizing bare areas will reduce the likelihood of the seed bank germination, minimize annual type germination and keep the existing perennial biotypes adapting. PGRs have also been enhancing poas adaptability to compete on low height of cut surfaces, by forcing the poa plant to level out its hill and valley growth pattern. By denying the growth surge, the poa plant is forced to conserve energy over seed pulse period. Saving it for use through the stressful summer periods, this improves its competitive ability to the otherwise summer bentgrass advantage. While sometimes unavoidable, the seed bank can still release early stage diploids and set you back, but the goal should be to encourage its perennial attributes by aerating in early to late summer during the seed head pulse. Try using 3-6" centers with Ω 0.5" tines to maximize recuperative times and heal quicker for a dual benefit - getting conditions back up. Where older diploid poas exist, the preferred method for renovation of one or more greens on a predominantly old poa course, is to aerate and sprig out the diploid plugs back onto the new surface. This technique will provide the best opportunity to maintain consistency while undergoing multi-year greens renovations. Jason Pick is an Instructor in the Turf Management Program at Olds College and a WCTA Director. 44 WESTERN CANADA TURFGRASS ASSOCIATION IMAGE COURTESY USGA