High-traffic areas demand extra attention

One-week-old perennial ryegrass.

The amount of games a field can host is directly related to how much grass cover is present, so the aim is to enter the playing season with 100 percent desirable grass cover. Having a full stand of healthy, mature grass is the best defense against divoting and wear as the playing season progresses, as well as offering the safest playing surface for the athlete. However, with all the best intentions and preseason planning in the world, once the playing season gets underway there are specific areas on fields that always get worn away or thinned. These are referred to as the high-traffic areas and they include:

  • Soccer and lacrosse goalmouths
  • Referee (linesmen) runs on soccer fields
  • The center of football and rugby fields
  • Sidelines of all fields
  • Baseball walk-out paths, behind home plate, umpire positions, outfield position areas, middle infield position area and in front of the pitcher’s mound
  • Entry and exit points on all fields

In these areas, traffic can be so intense that grass cover is lost fairly quickly and regular overseeding becomes part of the routine maintenance schedule. The benefit of overseeding then is primarily associated with providing field users with a high-quality, wear-tolerant, dense stand of turf. Additionally, a strong overseeding program helps crowd out weeds on athletic fields. Weeds like white clover, prostrate knotweed and crabgrass that can grow in compacted soils can be somewhat controlled/crowded out by persistent overseeding.

Classic wear in front of the pitcher’s mound.

When to overseed

The ideal approach to overseeding athletic fields would be to apply seed whenever bare soil or thin turf is visible in high-traffic areas. Overseeding the entire field, particularly outside of the high-traffic areas where there is dense turf, is a waste of time and money.

Many years of research in the golf course management industry have shown that there is little to be gained by overseeding one type of grass over another in the hope of changing the composition of the sward, because the mature, existing grass prevents the seed from germinating. Thus, overseeding should be restricted to high-traffic areas. On heavily used municipal fields this might mean overseeding high-traffic areas every week. Fields that are used less frequently might require overseeding only once or twice a month. At the end of the playing season more aggressive renovation and overseeding might take place over the entire field, particularly if surface levels, accumulated organic matter or severe soil compaction needs addressing at the same time.

In southern and transition areas of the U.S., bermudagrass sports fields that host late fall or early spring sports are oftentimes overseeded with ryegrass so that when the bermudagrass goes dormant and brown from late fall to spring the field remains green. The ryegrass turf grows in the dormant bermudagrass base, providing a playing surface that is green and able to recover from traffic. The ryegrass can also be striped with a mower to produce an aesthetically pleasing field, which might be a factor during a televised event or championship game. The ryegrass, if it is dense enough, will also compete with winter weeds like Poa annua. The transition from bermudagrass to ryegrass in the fall and then the reverse transition from ryegrass back to bermudagrass in the late spring is a challenging process for a sports turf manager. It involves a sound knowledge of both grasses and how they respond to irrigation, fertility, cultivation, growth regulators and mowing. In addition, soil and air temperatures have to be monitored closely.

A growth blanket/cover, or, as they say in Europe, germination sheet, can be used to enhance seed germination and establishment.

There are many sports field managers and turfgrass academics that discourage the process of overseeding bermudagrass with ryegrass, not just because of the intensity of the cultural management, but also because the bermudagrass does not respond well to the transition process in the spring. They feel that bermudagrass comes out of winter dormancy and produces a high-quality playing surface much quicker if it has not been overseeded with ryegrass the previous fall. Suggestions for extending the growing season of bermudagrass so that ryegrass does not need to be overseeded into it includes the use of more cold-tolerant bermudagrass cultivars, growth blankets and green dyes, as well as having a strong fertility program in place. For more detailed information on the transition process, visit the STMA website (www.stma.org) and look for “field maintenance resources.”

Overseeding grasses

Grasses used for overseeding during the playing season need to germinate and establish quickly, which rules out Kentucky bluegrass and tall fescue. These cool-season grasses are ideal for athletic sports, and maintenance programs should be in place to make sure they are added to the field as much as possible during renovations, but they are not quick enough to provide green cover between games.

“Quick” grasses can be listed as:

1. Perennial ryegrass

2. Annual ryegrass

3. Transitional ryegrass

4. Festulolium – a forage grass that does not like low mowing heights or traffic, but grows rapidly.

Classic wear in the middle of a football field.

These grasses typically germinate in three to five days. Festulolium and annual ryegrass can germinate in as little as three days if environmental conditions are favorable. Favorable conditions mean 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. If these grasses are irrigated and fertilized, they can provide green cover in a few days. The process can be enhanced even more if growth blankets are used, which not only encourages quick growth, but also discourages field users from going onto the field during renovations.

Overseeding rates

Seeding rates during overseeding are typically higher than seeding rates used to establish a permanent stand of turf. We have seen some success with rates at 10 pounds per 1,000 square feet per week. Remember the seed only needs to be applied to high-traffic areas. Research by Dr. David Minner found that annual ryegrass had a seeding rate ceiling of 90 pounds per 1,000 square feet, or 18 times the normal seeding rate of 5 pounds per 1,000 square feet. The conclusion for all overseeding research would suggest that higher rates than normal are appropriate during traffic.

The question of whether a “seed bank” can be built up is not quite as clear-cut. Perennial ryegrass has a short dormancy in that it is viable and ready to germinate without extended periods of chilling or other preconditioning. The dormancy of perennial ryegrass is broken when the seed is moist and it has gone through a short cycle of diurnal temperature variations over three to five days. Once the radicle (first root) has emerged and cell division is taking place, the seed has officially germinated. If moisture has caused some cell expansion but then the seed dries, it could possibly survive, but once there is cell division, moisture must be continually provided or the seed will die. For a viable seed bank to build up, the seed must be in the soil but not subject to moisture or the other germination triggers, which is highly unlikely if the seed has been broadcast on the surface and subjected to daily irrigation. To that end, the seed should ideally be applied on a weekly or biweekly basis, rather than just once at the beginning of the season.

Under intense traffic, there is little evidence to suggest that young seedlings survive for very long (hence the high seed rates). Young seedlings can offer some green cover if there is adequate time between games for it to establish, but if daily games are taking place, even the most rigorous of species will succumb. That is not to say that overseeding programs do not work, because as soon as there is a rest period, some of the seedlings will have the chance to produce tillers and mature into plants that can withstand traffic.

Application method

Broadcast seeding, by hand or spreader, prior to games has become a standard method of seed delivery to high-traffic areas, based mainly on testimonials among sports turf managers. There is also some data to back this up. Our research showed that slit seeding during heavy traffic caused significant surface damage and was probably not the best seed delivery method. Broadcast seeding appears to offer the best results without causing soil surface damage, though ideally the seed should be lightly raked in to maximize seed-to-soil contact.

Slit seeders are a great tool for making sure the seed gets into the soil surface, but they cause too much surface damage during heavy traffic.

Tips for overseeding success

Seedings generally fail due to a lack of moisture. The seed must be kept in a constant moist state in order to germinate, so syringing (lightly wetting, not watering) the seed four or five times per day is critical during the overseeding process.

Excessive watering leads to poor root growth, poor turf growth and higher disease incidence, so always apply water judiciously and avoid watering in the early evening to minimize the risk of disease.

One method of ensuring seed germination with limited water is to pre-germinate the seed. This involves soaking a bag of seed in oxygenated/fresh water for 48 to 72 hours (draining and resoaking regularly), and then mixing the seed with sandy soil/straight sand and fertilizer. This is called a divot mix because it is particularly helpful for small areas (divots).

In addition to moisture management, fertilizer applications are crucial to enhance the establishment speed. Research by Dr. Anthony Koski 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.

If a regular overseeding program is in place, it is important that preemergent herbicides use is carefully monitored. Preemergent herbicides are used to prevent the germination of unwanted weed seeds, but at the same time can inhibit germination of grass seed. This also applies to corn gluten meal, which is used not just as a natural organic fertilizer, but also as a natural preemergent herbicide. In research conducted by Dr. Dave Gardner many years ago, he found that corn gluten meal prevented germination of perennial ryegrass seed. Siduron (Tupersan) and mesotrione (Tenacity) are two herbicides that can be used at the same time as seeding, but it is essential to read the label when using any chemical control products during the overseeding process.

Drop/broadcast seeding (left), versus slit seeding, during heavy-traffic research.

Young seedlings, particularly ryegrass seedlings, are more susceptible to diseases like Pythium, brown patch and gray leaf spot. When environmental conditions are favorable for those diseases, it might be pertinent to buy apron-treated seed (seed coated with fungicide) and have a preventative fungicide program in place.

Growth blankets/covers can significantly enhance the overseeding process by retaining heat and moisture and preventing people from using those areas. They are particularly useful for small areas like soccer and lacrosse goalmouths because one person can move them easily if the area needs to be mowed or fertilized. Topdressing after seeding is another way to cover seed and retain heat and moisture. Topdressing is also used to control surface playability and organic management, but not many school and municipal field managers have the manpower or the budget to be on a topdressing program. A lightweight cover may be the answer in that situation.

Regular mowing has a significant effect on seed establishment by encouraging new tillers, which, in turn, produces denser turf.

Nondisruptive aeration equipment with solid tines can help keep the playing surface open and free draining without interfering with games.

Persuade your facility to buy you a light rack so you can grow grass year-round.

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