Overseed northern sports fields with bermudagrass

Premier athletic fields exhibit lush, high-density turf. But even on the best fields, conditions deteriorate when play increases or severe weather strikes. In heavily trafficked areas where turf density drops significantly, you must re-establish an acceptable level of turf density. Otherwise, you severely compromise playing conditions and increase the risk of player injury.

In the northern United States, field managers usually overseed worn areas on athletic fields when the fields aren't being used-for schools and many other venues,that occurs at the end of the "cool season" and the beginning of the "warm season." The timing makes it hard to establish cool-season grasses that are commonly used in overseeding-perennial ryegrass, and, to a lesser extent, Kentucky bluegrass or tall fescue.

The result? In the fall, fields are often worn to bare ground after a few events, and overseeding becomes necessary every year.

One solution: use bermudagrass for overseeding.

Bermudagrass is much easier to establish during the summer and has excellent wear tolerance. Its major disadvantage is that, as a warm-season grass, it will go dormant soon after the first frost in the fall, and most Northern winters will kill it off. Nevertheless, if you have to reseed each year, why not do so with a species that is more adapted to your reseeding schedule?

Locations and traffic treatment To investigate the potential for using bermudagrass as an alternative overseeding species in northern climates, I, along with Dr. David Minner (of Iowa State University) and Dr. Steve Keeley (of Kansas State University) conducted research at three locations in 1998 and 1999: Ames, Iowa, Manhattan, Kan. and Lincoln, Neb. In 1998, the Kansas and Nebraska plots were situated on well-used intramural fields. The traffic "treatment" consisted of the actual intramural sports taking place. In 1999, to better control traffic treatments, we moved the Kansas plots to the Rocky Ford Turfgrass Research plots near Kansas State University and the Nebraska plots to the John Seaton Anderson Turfgrass and Ornamental Research Area north of the University of Nebraska-Lincoln.

In Kansas, we imposed traffic treatments with a four-wheel Cushman Truckster by driving back and forth across the plots so that each square foot of the plot area received 24 passes. We simulated shear-traffic by driving at a uniform speed in a circular pattern with a constant radius so that each square foot of the plot area received four passes. The turning action of the rubber tires on the turf resulted in the shearing effect. In Nebraska in 1999, we used a modified Brinkman traffic simulator fitted with cleats to simulate shearing foot and vehicle traffic. In Iowa, the research took place at the Iowa State University Horticultural Farm where traffic was simulated with methods similar to those at Nebraska in 1999. At all three locations, we imposed the traffic treatments weekly from early-September to mid-November. Treatments were set up to simulate a minimum of 20 football games.

Overseeding treatments Table 1 (below) lists the over-seeding treatments. In 1998, we planted the perennial ryegrass/bermudagrass treatments together as a mix. However, in 1999 in Nebraska and Iowa, we seeded the bermudagrass entries in May, followed by a perennial ryegrass overseeding in early August. In 1998, we seeded control treatments of traditional cool-season grasses (tall fescue in Kansas and Kentucky bluegrass in Nebraska and Iowa) for comparison purposes. We also evaluated a Kentucky bluegrass sodded control in Nebraska in 1999. After overseeding, the plots received typical management for their respective regions.

Our data primarily consisted of visual ratings of percent ground cover. After the first frost at all three sites, the bermudagrass cover data was for dormant turf. Results were not consistent from location to location, but were similar from year to year in all locations. Because of this, the following results include a summary of 1998 data and a more thorough coverage of the 1999 results. At this writing, 1999 results for the Iowa location were unavailable.

1998 Summary In Kansas, ground cover for all entries was 100 percent before traffic started. By November, the tall fescue and perennial ryegrass controls had less than 10 percent cover, while the bermudagrass entries had an average cover estimated to be more than 60 percent. Some of the bermudagrass entries had 80 percent cover as late as November. The cover ratings for the bermudagrass/ryegrass entries were higher than bermudagrass alone and, depending on bermudagrass cultivar, had up to 15 percent more cover than bermudagrass without perennial ryegrass. Similar results occurred in Iowa. The bermudagrass plots showed 25 percent more cover in October than the ryegrass or bluegrass plots. No data was taken in Nebraska after September because a 4-inch rainfall followed by a major flag-football tournament severely damaged the intramural fields.

1999 Results * Nebraska. Biweekly injury observations began on September 13 and continued through October (see Table 2, above). Establishment of the overseeded perennial ryegrass was poor and bermudagrass dominated the overseeded plots. Differences between turf injury from the wheel and from the cleated part of the traffic simulator were evaluated separately. Perennial ryegrass and Kentucky bluegrass sod showed the lowest amounts of damage on Sept. 13 and 22, and Oct. 5. Observations in October showed that all the bermudagrass had gone dormant, although cover remained relatively high at 70 to 90 percent, even in trafficked areas. Perennial ryegrass and Kentucky bluegrass were still green at this time, with the ryegrass maintaining 100 percent cover in the tire and cleat tracks and Kentucky bluegrass (both sod and seeded blend) having 50 to 60 percent cover in tire tracks and 100 percent cover in the cleat tracks.

* Kansas. We rated plots for percent cover and visual quality on a biweekly basis beginning on Sept. 15, 1999 and ending on November 11. We also evaluated percent cover using a grid on Sept. 15 and Nov. 11.

- Percent cover. All treatments except the ryegrass check were at or near full cover by the time traffic treatments began (see Table 3, below). Full cover, or near full cover, was achieved in less than 2 months with the treatments that included bermudagrass. By Sept. 15, the ryegrass check had only about 60 percent cover and this was virtually all goosegrass. Poor establishment of the cool-season perennial ryegrass was not surprising in view of the mid-May seeding date. The treatments containing bermudagrass competed much better against goosegrass, although multiple applications of MSMA and quinclorac were still necessary. All bermudagrass-containing treatments maintained greater than 90 percent cover through the mid-October rating.

While all the bermudagrass-containing treatments showed significantly better cover than the ryegrass check on Sept. 15, Sept. 30, and Oct. 13, no significant differences in cover existed among the bermudagrass cultivars. Percent cover declined significantly in the bermudagrass-containing treatments at the Oct. 29 and Nov. 11 rating dates. The rapid decline was due to the decreased ability of the bermudagrasses to tolerate traffic as the weather cooled and its growth slowed. No significant differences in cover existed among any treatments at the latter two dates. Cover in the ryegrass check plots remained fairly stable during late October and early November.

- Visual quality. No consistent significant differences in visual quality occurred among bermudagrass cultivars during the study (see Table 4, page Contractor 6). However, visual quality of all bermudagrass-containing treatments was significantly better than the ryegrass check on Sept. 15, Sept. 30 and Oct. 13. By Oct. 29, quality of the bermudagrass-containing treatments had declined to the point where they were not significantly different from the ryegrass check. Overall, quality of the bermudagrass-containing treatments was fairly good to good on Sept. 15 and 30, fair on Oct. 13, and poor on Oct. 30 and Nov. 11. Quality of the ryegrass check treatment was poor on all rating dates.

Conclusions and recommendations Based on these studies, we feel bermudagrass is a feasible alternative on athletic fields in the northern United States when the window of opportunity for overseeding occurs during the heat of the summer. The primary advantages:

* Seeding can take place in the late spring and summer when conditions are favorable for bermudagrass growth. Because of the vigor of bermudagrass during hot weather, attaining excellent field quality for the fall sports season is easier than with cool-season grasses, which are under stress during the summer.

* The cost of improved bermudagrass seed is comparable to that of cool-season species. * The aggressiveness and wear tolerance of bermudagrass make it well suited for athletic-field use.

The primary disadvantages: * The field will be dormant, or nearly so, for the last few games of the season. Thus, as the season progresses, traffic tolerance and recuperative ability of bermudagrass drops.

* Bermudagrass requires annual reseeding because most seeded cultivars do not survive cold Northern winters.

A good strategy is overseeding bermudagrass fields with perennial ryegrass for fall sports use. Bermudagrass provides a strong base, and the ryegrass provides increased traffic tolerance and green color for the latter part of the season.

Seeding the perennial ryegrass at the same time as the bermudagrass, as we did in this study, will not give the desired results. For improved recuperative ability and color, field managers should seed the ryegrass in mid- to late August (about 2 weeks before the first game) at a rate of 10 to 20 pounds per 1,000 square feet. Alternatively, a green turf dye could achieve similar results.

If you cannot afford ryegrass overseeding, you can use a bermudagrass monoculture, but realize that recovery from traffic will be minimal to nonexistent toward the end of the season.

Bermudagrass cultivars did not differ in their cover or quality in these studies. We expect that most of the elite, improved bermudagrass cultivars currently available should provide similar results.

Dr. Roch Gaussoin is an extension turfgrass specialist at the University of Nebraska (Lincoln, Neb.); Dr. David Minner is an extension turfgrass specialist at Iowa State University, (Ames, Iowa); Dr. Steve Keeley is an extension turfgrass specialist at Kansas State University (Manhattan, Kan.). This work was funded in part by a grant from Seeds West, Inc.

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