Introduction:   Recently released seeded bermudagrass varieties such as Riviera offer quality and cold tolerance equal to the best vegetative types and the ability to seed damaged areas.   Most athletic fields in Virginia consist of mixtures of Kentucky bluegrass and perennial ryegrass.   These grasses do not perform as well as bermudagrass during summer months and are more costly to maintain due to disease and water requirements.   Although it is desirable to convert athletic fields to bermudagrass, most athletic fields and golf fairways must remain in play during the summer.   Research funded by the Virginia Turfgrass Foundation has shown that seeded bermudagrass is difficult to establish in mature turfgrass unless the turfgrass canopy is disrupted for a brief time.   Killing narrow strips was shown to promote 25 to 50% seeded bermudagrass establishment in a single season without reducing turfgrass quality as viewed perpendicular to strips.   Our previous work was conducted with a sprayer that killed a two-inch strip on twelve-inch spacing.   We hypothesized that bermudagrass establishment could be increased by selecting an optimal frequency and width of kill strips.

Research Methods:   Experiments were established in May 2005 in Blacksburg, VA on a 3/4 inch Kentucky bluegrass fairway at the old VT Golf Course to evaluate five variations of strip frequency and width.   Two-inch wide strips were killed on 12, 8, and 4 inch spacing and one-inch strips were killed on 5 and 3 inch spacing.  These treatments are equivalent to killing 17, 25, 50, 20, and 33% of existing turfgrass.   Strips were killed with glyphosate (Roundup) at one quart per acre.   We core cultivated the area in one direction and vertical mowed in one direction prior to seeding with Riviera bermudagrass at one pound pure live seed per thousand square feet.   Plots were sprayed in the morning and seeded in the evening on May 12, 2005.

Research Results:  Bermudagrass cover increased as percent kill of cool-season turfgrass increased.   On October 8, 154 days after seeding, bermudagrass cover ranged from 42 to 100% as the amount of cool-season turf kill increased from 17 to 50%.   The level of bermudagrass cover (42%) obtained when 2 inches of turf was killed on 12 inch centers, was consistent with previous work that evaluated the strip kill method with the same strip width and frequency.   At 47 days after treatment, turfgrass quality was equivalent when plots were viewed perpendicular to strips but quality was not acceptable when viewed along strips of 2 inches kill on 4 inch centers and 1 inch kill on 3 inch centers.   At 66 days after seeding and beyond, turfgrass quality was equivalent between all plots.  

Recommendations:  Converting cool-season athletic fields and golf fairways to seeded bermudagrass can be achieved slowly with minimal reduction in turfgrass quality or quickly with increasing reduction in turfgrass quality.   Minimal bermudagrass establishment can be achieved by simply seeding into established cool-season turfgrass.   However, on athletic fields that have been worn due to sports play, open areas in the turf would contribute to seeded bermudagrass establishment in the same way as killing narrow strips.

• Most rapid bermudagrass establishment occurs when 33% or more Kentucky bluegrass is killed in a strip fashion.

• Manage turf for bermudagrass, not cool-season grasses.   Increase fertility in summer months, decrease mowing height and water use.

• In subsequent growing seasons after at least 50% bermudagrass cover is achieved, use a selective herbicide such as foramsulfuron (Revolver) or trifloxysulfuron (Monument) to eliminate cool-season grasses and promote complete conversion to bermudagrass.

Virginia Tech Researchers: Shawn D. Askew, Ph.D., Assistant Professor of Weed Science; Mike Goatley, Ph.D., Associate Professor of Crop, Soil, and Environmental Sciences.

Sponsors:  Virginia Turfgrass Foundation, Virginia Turfgrass Council, Virginia Agriculture Council.