To determine if seeded bermudagrass can be established in the summer and then used for intensely trafficked sport fields in late summer/early fall.

This is a cooperative research project with Dr. Roch Gaussoin, University of Nebraska, and Dr. Steve Keeley, Kansas State University. Field plots were also established in Kansas and Nebraska, but only the Iowa data is reported at this time. This field research project was established at the Iowa State University Horticulture Research Station, Ames, IA. On 19 June 1998 the study area was prepared by treating the existing stand of grass and weeds with glyphosate. Eleven days later all of the vegetation was dead and approximately 50 percent of the area was showing exposed soil. On 2 July 1998 the test area was verticut in two directions to a depth of 0.5 inches. The area was immediately fertilized, seeded, and watered. One pound of N, P₂0₅, and K₂0 was applied per 1000 sq. ft. Six bermudagrass varieties (3 lbs. seed /1000 sq. ft.) and Bright Star perennial ryegrass (15 lbs. seed/1000 sq. ft.) were established in 8 foot by 15 foot whole-plots. Grass was watered and mowed to a two-inch cutting height. Plots were rated on 24 August and then half of each bermudagrass whole-plot was slit seeded with Bright Star perennial ryegrass (10 lbs/1000 sq. ft.) to provide a 4-foot by 15-foot split-plot. The experimental design was a randomized complete block with seven whole-plot treatments (bermudagrasses: Sultan, Numex Sahara, SWI-10, Blend C, Mirage, and Pyramid), two split-plot treatments (with or without perennial ryegrass), and three replications.

In 1999 treatments were established on the same plots that were used in 1998. The intent was to keep any existing vegetation (bermudagrass or perennial ryegrass) that may have overwintered in the plots. Sports field managers are reluctant to kill any vegetation in high traffic areas and re-establishing into the existing vegetation in this manner provided a realistic approach to providing maximum cover during the summer. By mid-June it was evident that no bermudagrass had survived the winter and the split plots containing only bermudagrass contained about 50% Poa annua. To maximize desirable turf cover the only plots treated with Round-up were those that received 100% bermudagrass. The 100% perennial ryegrass plots and the bermudagrass plots overseeded with perennial ryegrass were not treated with Round-up. Round-up was applied on 10 June and all plots were seeded on 15 June 1999. Seeding and fertility rates were the same as in 1998.

Traffic was applied with a Brouwer roller that was modified with football cleats to supply differential-slip-type traffic. Fifteen passes over the test area were made with the traffic simulator between 27 August and 15 September 1998 and 60 passes were made between 16 September and 24 October in 1999

Table 1 shows the advantage of establishing a warm season grass like bermudagrass during the summer compared with perennial ryegrass. On 24 August all of the bermudagrass selections had greater than 90% turf cover, while perennial ryegrass had only 23% turf cover. This resulted in a substantial advantage that would coincide with the beginning of a normal fall football season. Even with an additional perennial ryegrass seeding on 24 August, the bermudagrasses provided more turf cover than perennial ryegrass at the end of the football season. Bermudagrass cover was approximately 75% compared with 52% for perennial ryegrass (Table 2).

All of the bermudagrass varieties retained 100% of their green color on 15 September. By 1 October the bermudagrasses were showing signs of winter dormancy and green color retention was approximately 60 percent. By 16 October 1998 bermudagrass leaves were mostly brown with only about 30% green tissue present. Table 2 shows that there was a slight improvement in turf color on 16 October when bermudagrass was overseeded with perennial ryegrass. By 16 October the perennial ryegrass only treatment had much better color than the bermudagrass or the bermudagrass/overseeded with rye treatments.

In mid-June 1999 it was evident that no bermudagrass survived the winter and the plots seeded with only bermudagrass had approximately 50% cover by Poa annua. The winter-killed bermudagrass plots that were contaminated with Poa annua were treated with Round-up on 18 June in preparation for seeding. Just as in 1998, all the plots were again seeded in early July 1999. The difference in 1999 was that the perennial ryegrass and ryegrass plus bermudagrass treatments already had some residual established turf from the previous 1998 season. Any treatments that received perennial ryegrass in 1998 had approximately 50% perennial ryegrass at time of seeding on 1 June 1999. Table 3 shows the effect of interseeding bermudagrass and perennial ryegrass into this situation. The residual perennial ryegrass from 1998 combined with the additional seeding in 1999 resulted in a 90% turf cover stand. In 1998 the summer seeding of perennial ryegrass on bare ground only produced 23% turf cover. This is a good indication of why athletic field managers do not like to start over by killing existing vegetation, even though it may be sparse. When the mixture of bermudagrass and perennial ryegrass was seeded into the existing 50% stand of perennial ryegrass, it appeared that the bermudagrass would only establish where there was bare ground or exposed soil. This resulted in a stand of approximately 25% bermudagrass and 75% perennial ryegrass at the beginning of the fall traffic period compared to the bare ground plots that when seeded with 100% bermudagrass resulted in 100% turf cover (Tables 1 and 3).

There was very little difference among bermudagrass varieties in terms of turf quality or cover as it relates to traffic. The most compelling result for using bermudagrass for summer overseeding in the north is evident from the amount of bare ground or exposed soil data (Table 3). At the end of the fall traffic period perennial ryegrass alone resulted in 37% of the ground having exposed soil, while bermudagrass alone or mixed with perennial rye had less than 10% exposed soil.

This study has shown that seeded bermudagrass can be used to quickly establish grass on intensely trafficked cool-season fields. While it does not over winter, it has provided better turf cover and less exposed soil compared to conventional overseeding only with perennial ryegrass. Turf quality in terms of color and texture are of little importance to the athletic field manager who is battling excessive traffic. Germplasm that specifically addresses the issue of turf cover should not be overlooked just because it has less appeal from a visual quality basis.

Listed below are some of the desirable characteristics for selecting seeded bermudagrasses that could be used for annual overseeding of cool season grasses in northern climates.

Table 2. Turfgrass color, quality, and %cover on 16 Oct 1998 at the end of the simulated traffic season.