Safety is the greatest concern for any sports field manager. As long as the field is safe for the players, then everything else will fall into place. A safe field consists of an even, consistent surface with no holes or undulations, and ideally has 100 percent desirable grass cover to provide the athlete with shock absorbency.

 

During a game, it is common to see pieces of the turf ripped up, particularly when it is raining. In Kentucky bluegrass and bermudagrass, these divots can be quite large, possibly because these grasses have an interwoven mat of rhizomes that pulls out in large clumps. In contrast, bunch-type grasses, such as perennial ryegrass, tend to produce small clumps of tissue.

Applying divot mix by hand.

The size of the divot depends on the athlete and the maneuver. It isn’t difficult to imagine the amount of damage caused by a 6-foot-tall, 200-pound professional soccer player performing a sliding tackle, or a football player changing direction quickly and cutting into the turf. The type of rootzone also affects the frequency and severity of divots, with sand-based rootzones more prone to divots due to their low shear strength. Field managers have also reported seeing an increase in the amount of divot damage recently caused by the cleat length and design on new athletic shoes. In essence, the longer and more dense the cleat pattern, the more aggressive the divot injury.

Divot prevention

A turf sward with a deep, healthy root and rhizome system is less prone to divots than a thin, unhealthy sward. Sound cultural practices like deep tining, spiking and verticutting done in the spring and fall will keep the playing surface and underlying soil open and free from compaction. Done in conjunction with topdressing, these practices are the foundation of any turf management program. Fertilizer and water also greatly contribute to the health of turf roots and should be done judiciously during those times of the growing season where root growth can be maximized. However, too much fertilizer and water can have a detrimental effect on turf roots.

In addition to cultural practices, there has been some research to suggest that applications of the plant growth regulator trinexapac-ethyl, applied prior to the beginning of the playing season, can help prevent divots. Research at Penn State (Serensits, 2008) showed that applications of trinexapac-ethyl made monthly from May to July resulted in smaller and less frequent divots on Kentucky bluegrass turf under traffic during the fall playing season. There have been similar results at Ohio State, whereby fall-applied trinexapac-ethyl resulted in increased traffic tolerance the following spring. Both of these studies suggest that trinexapac-ethyl could be used as a preseason conditioner to improve traffic tolerance during the playing season.

Divot repair

Walking across the field during halftime and immediately following a game is an important practice because it offers the opportunity to replace or remove divots quickly. In some cases, if the divot is large enough, it is possible to put the divot back where it came from and compress the area to maximize divot-to-soil contact. The extent to which the divot will reestablish depends upon how quickly it is replaced and the immediate care it receives. The most important factor is moisture, because if divots are allowed to dry out, they will do so quickly and die. For this reason, it is more common to remove divots from the playing surface and later fill in bare spots and holes with a divot mix.

Once the divot and all other organic material (leaf tissue, thatch) has been removed, the bare area needs to be prepped for new seed. On a small scale this can be accomplished with a divot fork or divot repair tool similar to the ones used on golf green divots. The hand-held fork is used to gently lift the surface and surrounding area and create a soil tilth or seedbed. On a larger scale this can be accomplished with a long-handled fork or garden weasel.

Divot mixes

The main material used in a divot mix is pure sand for sand-based fields, and good quality sandy loam topsoil for native soil fields. Commonly used material mixes include: 100 percent pure sand, a 50-50 mix of sand and soil, an 80-20 mix of sand and peat (or other organic), or other combinations of these materials. Ideally, the mineral material used in the divot mix should match the existing rootzone.

The next ingredient in the divot mix is seed. Fast-establishing species like annual ryegrass, transitional ryegrass and perennial ryegrass are commonly used in divot mixes because they offer the best opportunity to get some kind of ground cover in place prior to the next scheduled event. If there is a longer establishment time available, slower growing species like Kentucky bluegrass can be used. Some field managers prefer to persevere with Kentucky bluegrass, as they do not want perennial ryegrass to take over their fields.

A 50-50 mix of Kentucky bluegrass and perennial ryegrass is common. It is important to match the color of the new seed variety with the existing stand of turf, especially with Kentucky bluegrass, which varies greatly in color from light green to the darker Midnight types. Ryegrasses typically germinate in three to five days, with Kentucky bluegrass and bermudagrass germinating in seven to 10 days if conditions are favorable. Favorable conditions means that the soil temperature is consistently above 50 degrees Fahrenheit and there is adequate moisture for germination. The growth initiation temperature for perennial ryegrass is 41 degrees Fahrenheit. Growth stops at approximately 86 degrees Fahrenheit, and optimum growth occurs at 68 to 77 degrees Fahrenheit.

Repaired divots.

If these grasses are irrigated and fertilized, they can provide green cover in a few days. The process can be further enhanced if growth blankets are used. Growth blankets not only encourage quick growth, they also discourage field users from coming onto the field while renovations are taking place.

Divot repair is carried out during the entire playing season, both during and after the game. During the cooler months divot recovery can be painfully slow, but there are things, like pregerminating seeds, that can help expedite the process.

There are several ways to get the best out of the divot repair process: seed can be coated (“Apron Coated”) with a fungicide to prevent summer seedling diseases like Pythium; seed can be coated with a liquid fertilizer or seaweed, which will provide nutrition to the newly emerging seeding; or seed can be pregerminated.

Using a garden weasel.

For pregerminating, the seed is soaked in water for 24 to 48 hours prior to use. It’s important to keep oxygen flowing through the water, either by draining the water every 12 hours and replacing it, or feeding the tank with an air line. Once the seed has been soaked there’s no turning back; if the seed dries out again it will die. After 24 to 48 hours, the pregerminated seed is added to the divot mix. The mix cannot be applied with a drop or rotary spreader as it is too wet and will clog up the spreader, so it is usually applied to bare spots by hand. It can be dried out just prior to spreading, but seedling mortality is a concern.

More details on this practice can be found in an Iowa State University Extension Bulletin, “Pregerminated Divot Mix for Repairing Athletic Fields” (http://apps.hort.iastate.edu/turfgrass/extension/EGathfldpregerm.pdf), by Mike Andresen, CSFM, and Dave Minner, extension turfgrass specialist.

While some field managers will only use rootzone material and seed in their divot mixes there are other products that can be added:

  • Green dye or green sand is used to mask the color of the divot mix. Another way to mask turf damage from the stands/bleachers is to spread grass clippings over the damaged areas just prior to the game. As game time approaches, the fresh green clippings are spread on the bare spots. This will give the illusion, from the stands, that there is grass on the field. With this technique, timing is key. There is a three-to-five-hour window before the clippings start to turn brown, but for most sporting events, that is enough time. A final way to mask damage is to put a logo of some kind on the field. By having an on-field logo and crisp, white painted lines, it takes the fans’ focus off the turf damage. This can also be done with the use of creative mowing patterns.
  • Internally porous inorganic amendments like calcined clay are sometimes used to conserve moisture. They are mixed with sand (for example an 80-to-20 mix of sand and calcined clay) and offer the benefit of moisture and nutrient conservation.
  • Starter fertilizer is typically added or applied directly after to provide nutrients to emerging seedlings.
  • Parts of the field that have a lot of divots, bare spots and thin turf can be covered with growth blankets or seed germination covers.

Divot fork.
Photo by Phil Sharples.

Divot aftercare

First and foremost, the successful recovery of a divot depends on the amount of moisture it receives. Seedings generally fail because of lack of moisture. In order for seed to germinate it must be kept constantly moist, so syringing the seed four or five times per day is critical during the divot recovery process.

In addition to moisture management, fertilizer applications are crucial to enhance the establishment speed. Some research even suggests that standard fertilizer applied at .5 and 1 pound of nitrogen per 1,000 square feet on a biweekly or monthly basis may be more effective for maintaining acceptable turf quality and density under traffic than overseeding, at least in the short term.

Regular mowing has a significant effect on seed establishment by encouraging new tillers, which in turn produces denser turf. Rollers on the mower will also help this process. In addition, nondisruptive aeration equipment with solid tines can help keep the playing surface open and free-draining without interfering with games or causing too much damage to newly seeded areas.

Lastly, if possible, limit foot and vehicular traffic on the field between events. By limiting the traffic on the field you increase the likelihood that the newly seeded divot areas will have a chance to germinate and survive.

Pam Sherratt is a sports turf specialist at Ohio State University and served on the STMA board of directors from 2010-2011.