SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.
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FieldScience | Brian F. Bornino Overseeding bermudagrass fields on the north edge of the transition zone B ERMUDAGRASS is widely used in southern and transitional zones of the United States for ath- letic fields. Its popularity is due to its recuperative potential via aggres- sive stolons and rhizomes and toler- ance to heat, drought, and low (≤ 1 inch) mowing. With improved cold hardiness in seeded and vegetative cultivars, bermudagrass has been pushed to the northern edge of the transition zone. The major draw- backs of use in more northern cli- mates are the possibility of winterkill and an extended dor- mancy period that results in a straw- brown appearance that can last from first frost in the fall until soil tem- peratures at a depth of 4 inches rise above 50°F; this is usually late May to early June in the northern transi- tion zone. To overcome this, turf managers routinely overseed bermudagrass athletic fields with a cool-season ryegrass mixture in late summer/early fall to achieve year- round color and improved aesthetic quality. Although dormant bermudagrass can withstand consid- erable traffic, overseeding can im- prove resiliency and performance under intense use. Overseeding bermudagrass also has its disadvantages. From an agro- >> THIS PHOTO OF ROSS-ADE STADIUM at Purdue was taken right before the last home game, November 20, 2010. The field has bermudagrass from wall to wall but is overseeded only inside the media lines; see the contrast of overseeded vs. non- overseeded. nomic standpoint, overseeding is basically growing two types of plants with different management requirements in the same location. Ryegrass out-competes the dormant bermudagrass for light, nutrients and water throughout the fall, winter and transition period in the spring. Another po- tential disadvantage is scheduling the overseeding within the optimum planting window without interfering with play on the field. Overseeding too early in the fall reduces establishment of the ryegrass seedlings due to the competi- tion with bermudagrass and the possibility of disease, whereas overseeding too late hampers establishment be- cause of reduced germination and seedling development in suboptimal temperatures. Although the majority of literature is geared toward the golf course industry, recommendations for overseeding rates of perennial ryegrass (PRG) range anywhere from 12 to 15 pounds pure live seed/1000 ft2/year for southern ath- letic fields. These recommendations were found to be very inefficient in the colder climate when they were followed the first year (2006) we had bermudagrass at Purdue Uni- versity’s Ross-Ade Stadium. In addition, while several of the studies evaluated the effect of seeding rates when planted on a single date, little research had been conducted evaluat- ing the impact of multiple overseeding events into bermudagrass turf. The objectives of this study were to de- termine optimum perennial ryegrass seeding rates for over- seeding bermudagrass athletic fields in the northern transition zone and to determine if multiple seeding events improved overall (PGR) establishment compared to a sin- gle seeding event. STUDY DETAILS The study was conducted at the Purdue University var- sity football practice complex in West Lafayette, IN, which is in the USDA Hardiness Zone 5a, approximately 220 miles north of zone 6a and 6b, which could be considered the transition zone between cool- and warm-season turf- grass adaptability. This site was selected because it provided a moderate amount of wear from the football team while practicing four times per week from August to November. The test plots were located just outside the hash marks in an area where the defensive backs ran their daily drills en- suring that each one received similar traffic. This gave us a more practical understanding of how the overseeding would respond to wear, rather than using the standard cleat simulator. The field was originally sodded with Patriot bermuda- grass in June 2006 and subsequently overseeded with Riv- iera bermudagrass in May 2007 after approximately 70% turf loss resulted from winterkill. This was a 2-year study that consisted of three application strategies and five seed- ing rates. Seeding rates of the perennial ryegrass blend were 12.5, 25, 50, 75, and 100 pounds/1000 ft2/year pure live 12 SportsTurf | June 2011 www.sportsturfonline.com By