8 Cultural Practices
Dense, healthy turf with adequate infiltration plays an important role in preventing runoff and erosion. Cultural practices promote both turf density and health, in balance with providing a high-quality playing surface. These practices include cultivar selection, mowing, aeration, surface cultivation, topdressing, and rolling.
8.1 Cultivar Selection
Site preparation, the choice of cultivar, and correct management practices are essential to establishing and maintaining turfgrass. Delaware is in the transition zone where the cool-season grasses (Kentucky bluegrass, perennial ryegrass, tall fescue, red fescue) are stressed during hot and humid summers, and the warm season grasses (Bermuda grass and zoysia grass) turn brown after a frost and can be invasive. Turf-type tall fescue is well adapted for Delaware and requires less fertilizer than bluegrass and ryegrass.
Numerous new turfgrass cultivars continue to be developed and released by turfgrass breeders. However, many of these cultivars are adapted to the environmental conditions that prevail in other regions of the country and are not adapted to the specific environmental conditions that occur in the transition zone. Thus, to identify cultivars that perform well in this region, extensive cultivar trials are evaluated each year at the University of Delaware and University of Maryland. The cultivar performance data obtained at various trial locations is often reviewed in a joint meeting of university researchers and representatives of the Department of Agriculture of Mid-Atlantic states.
The use of recommended cultivars usually results in a turfgrass stand of higher quality and density, greater stress tolerance, lower nutrient requirements, less water usage, and fewer pest problems. Also, the use of recommended cultivars generally has the benefits of greater water infiltration, reduced need for pesticide applications, reduced water runoff, and the enhancement of the environmental benefits of properly managed turfgrass.
The National Turfgrass Evaluation Program (NTEP) provides information on the testing and adaptation of the turfgrass cultivars, searchable by state and NTEP test location. Delaware will have tall fescue test data beginning in 2019 (Figure 17), but Maryland test results and recommendations can be reviewed and information from eastern Maryland is relevant for Delaware. When selecting cultivars for a specific site, considerations include desired use, site and microclimate conditions, disease resistance, and spring transition traits. For more information, see Recommended Turfgrass Cultivars for Certified Sod Production and Seed Mixtures in Maryland. 2017. University of Maryland.
Mowing is the most basic and perhaps the important cultural practice to consider when developing a management plan. Mowing practices impact turf density, texture, color, root development, and wear tolerance. Failure to mow properly results in weakened turf with poor density and quality.
Proper mowing height is a function of the quality of the cut, mowing frequency, the cultivar being managed, and the intended use of the site. Other factors influencing mowing height include mowing frequency, shade, mowing equipment, time of year, root growth, and abiotic and biotic stress. For example, mowing frequency affects turfgrass growth habit. Frequent mowing increases tillering and shoot density, but also decreases root and rhizome growth. Therefore, mowing practices should balance these two physiological responses to enable quick turf recovery through decisions related to height of cut, frequency, and mowing patterns. Mowing too infrequently results in alternating cycles of vegetative growth followed by scalping, which further depletes food reserves of the plants. Proper equipment maintenance is also key to maintaining healthy turf, as sharp mower blades reduce the risk of creating wounds that can favor microbial infection and, in some cases, dissemination of pathogens.
8.2.1 Height of Cut
In general, a taller turf offers a better defense to pests and other stressors, while a closer cut turf is often considered more aesthetically pleasing. Determining the best height of cut (HOC) requires balancing the stress response to mowing with golfer expectations of playability, staffing levels for mowing frequency, weather conditions, and budget considerations for the increased maintenance and inputs of lower HOCs. Especially at low turf heights (<1.5 inches), the corresponding reduction in root strength requires more intensive maintenance (e.g. water and fertilizers) to maintain turf density.
Ideal tolerance ranges for turf height vary by cultivar. The ideal range maximizes density, though staying within the tolerance range will provide adequate density assuming water, nutrients, etc., are provided optimally. Recommended golf course mowing heights for Mid-Atlantic turf species are found in Tables 6 and 7 below:
Table 6. Recommended minimum golf course mowing heights, by area (in inches).
|Turf Species||Greens Healthy Maintenance||Greens Tournament Play||Tees, Collars, Approaches||Fairways|
Table 7. Recommended mowing heights for roughs (in inches)*.
|Kentucky bluegrass||Perennial ryegrass||Tall fescue||Fine fescues||Bermudagrass|
|1.0 – 6.0||1.0 – 6.0||2.0 – 6.0||2.5 – 6.0||0.75 – 2.50|
Mowing height can also be varied seasonally to improve turf responses to changes in weather and available sunlight such as during spring greenup, summer stress, and cold hardening. For example, in the early spring, warm season grasses have a more prostrate growth habit and can be mowed closer without negatively affecting overall plant health. At this time of year, close mowing can control thatch, increase turf density, remove dead leaf tissue, and promote earlier greenup. In the summer, by contrast, a higher cut helps moderate stress through a variety of means such as insulating the crown from heat stress, reducing weed competition, and reducing water needs.
In shaded areas, shoots elongate to capture sunlight, resulting in a weakened root system. Therefore, the HOC should be raised to increase photosynthetic area and improve carbohydrate availability. Mowing stress can also be reduced by minimizing turning in these areas. In addition, a plant growth regulator (PGR) can be used as a regular management tool to control growth in shaded environments.
8.2.2 Mowing Frequency
Maintaining an optimal root-to-shoot ratio is critical. Following the traditional rule, mowing should be frequent enough so that no more than one-third of the top growth is removed at any one time. Removing more than 40% of the leaf area inhibits root growth because the grass will use more energy to regenerate new shoots than for sustaining roots. Published recommended mowing frequency during active growth based on various mowing heights is shown in Table 8 (republished with permission from Environmental Best Management Practices for Virginia’s Golf Courses, Table 7-3, p. 93):
Table 8. Mowing frequency based on various mowing heights.
|Mowing height (in inches)||1/3 rule height (in inches)||Frequency|
|0.12||0.18||Every 1 – 1.5 days|
|0.25||0.37||Every 2 days|
|0.5||0.75||Every 2 – 3 days|
|1.00||1.50||Every 3 – 4 days|
|1.50||2.25||Every 4 – 5 days|
|2.00||3.00||Every 5 – 6 days|
|3.00||4.50||Every 6 – 7 days|
|4.00||6.00||Every 7 – 8 days|
In addition to maintaining an optimal root-to-shoot ratio, mowing should only be performed when field and growing conditions are good. Turfgrass stressed by excessive heat, cold, moisture, drought, traffic, or damage from cultural practices should be mowed at a reduced interval or not mowed at all to aid recovery. When favorable conditions return and if the turf is excessively tall, scalping can be avoided by lowering HOC in small increments so as not to remove more than 30% to 40% of the leaf blade when mowing.
8.2.3 Mowing Patterns
Whenever possible, the direction of cut with mowing equipment should be altered to prevent excessive lateral growth (“legginess”) and to maintain the desired HOC. On greens, the direction should be changed every time it is mowed. On most features that are mowed, particularly on fairway-height or lower HOCs, a “clean-up” pass is made around the edge. The frequency with which this area is mowed can often be reduced to alleviate stress, especially in the summer. It may also be necessary to raise the HOC of the clean-up pass at times due to turf loss, thinning, scalping, or other issues negatively impacting the turf.
8.2.4 Mowing Equipment
Several types of mowers are available. Reel mowers are preferred for turf with low HOC (<1.5 inches) because they produce the best quality cut when compared with other types of mowers. Rotary mowers, when the blades are sharp and properly adjusted, deliver acceptable cutting quality for turf that will be cut above 1 inch in height. Flail mowers are most often used to maintain utility turf areas that are mowed infrequently and do not have a high aesthetic requirement. Mowing equipment should be checked daily after use to ensure the best possible quality of cut. Blades should be sharpened or adjusted as often as necessary to achieve this quality of cut as dull blades can have several undesirable physiological effects, resulting in shredding of leaf tissue, increasing water loss, and boosting the potential for disease.
8.2.5 Clipping Management
Whenever possible, grass clippings should be returned to the grass canopy. Clippings return provides multiple benefits, such as:
- Nutrient recycling of N, P, and K (e.g. up to 1 pound N per 1,000 feet2 per year) and other essential nutrients.
- Reduced need for supplemental nutrients.
- Elimination of the need to remove clippings to other areas of the facility or an off-site disposal area.
In areas where clippings cannot be returned (such as greens), they can be blown, dragged, or otherwise moved away, though they should not end up in or near stormwater treatment structures or wetlands. Alternately, clippings can be collected and composted. Composted clippings can be used as soil amendment or fertile topdressing during establishment of new tee, fairway, or rough areas. PGRs can also be used to reduce clipping production.
Cultivation practices – aeration practices and surface cultivation practices – disturb the soil or thatch through the use of various implements to achieve important agronomic goals that include relief of soil compaction, thatch/organic matter reduction, and improved water and air exchange. However, cultivation can require significant time for recovery, thus disrupting play, and should be used judiciously. Cultivation frequency should be based on traffic intensity, level of soil compaction, and the amount of accumulation of excessive thatch and organic matter, which reduces root growth, encourages disease, and creates undesirable playing conditions. Table 9 shows advantages/disadvantages of aeration practices.
Table 9. Turfgrass aeration methods and rankings of agronomic benefits.
|Method||Compaction Relief||Thatch control||Water/air movement||Disruption of play|
|Core aeration||High||Good||High||Medium to high|
|High-pressure water injection||None||Low||High||None|
8.3.1 Core Aeration
Core aeration is effective at managing soil compaction and aiding in improvement of soil drainage by removing small cores or plugs from the soil profile. Cores are usually 0.25 to 0.75 inches in diameter. Using bigger tines and therefore removing larger cores will disrupt play for longer.
8.3.2 Deep Drilling
Deep-drill aeration creates deep holes in the soil profile through use of drill bits. Soil is brought to the surface and distributed into the canopy. Holes can be backfilled with new root-zone materials if a drill-and-fill machine is used. These machines allow replacement of heavier soils with sand or other materials in an effort to improve water infiltration into the soil profile.
8.3.3 Solid Tining
Solid tining causes less disturbance to the turf surface and can be used to temporarily reduce compaction and soften surface hardness during months when the growth rate of grasses is reduced. However, the benefits of solid-tine aeration are temporary because no soil is removed from the profile, except when using a deep tine aerator with a “kicking action” that results in some soil loosening. “Venting” or “needle-tining” is often used to describe the practice of solid tine aeration using small-diameter tines (0.25 to 0.375 inches). This is an effective tool that can be used to help provide increased gas exchange to root systems and can be particularly useful in alleviating summer stress on putting greens. It can also be performed with minimal impact on putting surface quality when followed by mowing or rolling.
8.3.4 High-pressure Water Injection
High-pressure water injection promotes water penetration and air exchange. Steams of water are injected at high velocities 4 to 8 inches into the soil at 1/8 to ¼ inch diameter. High pressure water injection doesn’t disrupt play.
8.4 Surface Cultivation
Surface cultivation manages organic matter accumulation above the soil, reduces the formation of leaf grain, improves infiltration, and improves surface consistency (Table 10). While these methods are generally less disruptive than traditional aeration practices, they usually have a limited to no impact on soil compaction relief.
Table 10. Surface cultivation practices.
|Method||Compaction relief||Surface disruption||Water/air movement||Disruption of play|
|Vertical mowing||Low||Medium – High||Medium||Low – High|
|Grooming||None||Very low||Very low||None|
8.4.1 Vertical Mowing
Vertical mowing (verticutting) can be incorporated into a cultural management program to achieve a number of goals. The grain of a putting green can be reduced by setting a verticutter to a depth that just nicks the surface of the turf. Deeper penetration of knives will stimulate new growth by cutting through stolons and rhizomes while removing accumulated thatch. Deep vertical mowing (0.5 to 1 inch depth) removes a greater amount of thatch than core aeration and can be considered for aggressive thatch removal as it can remove up to 15% of the thatch at one time. However, it is aggressive and should only be done during less stressful times (e.g. cooler temperatures) and on well-rooted turf. Unlike deep mowing, shallow vertical mowing (0.5 inches or less) does not remove thatch. Instead, it severs stolons to promote new growth while also standing up blades for removal of old growth and minor canopy thinning. Shallow vertical mowing can be practiced regularly during the growing season except in times of drought or excessive heat.
Groomers, or miniature vertical mowers attached to the front of reels, are effective at improving management of grain and improving plant density through the cutting of stolons but provide very low or no relief for compaction or thatch.
Spiking/slicing reduces surface compaction and promotes water infiltration with minimal surface damage. Slicing is faster than core aeration but is less effective. Spiking can break up crusts on the soil surface, and improve water infiltration.
Topdressing the playing surface with sand is primarily done to improve surface firmness and smoothness, dilute thatch, improve recovery from turf thinning or cultural practices, and, over time, modify the root zone. Topdressing should be of a particle size distribution that is compatible with the existing soil medium to maintain even water distribution in the soil profile. The use of very fine materials can result in layering that impedes uniform water distribution. Topdressing practices can be described as heavy or light for different reasons:
Heavy topdressing, with sand depths up to 0.25 inches, following core aeration and vertical mowing, aids in recovery of turf. Rates can vary based on the various cultural practices that were performed but should not exceed the capacity that the turf canopy can absorb. The use of dry sand helps fill aeration holes completely in one application, as well as speed recovery.
Light and frequent topdressing is important for maintaining a smooth, firm, and uniform playing surface throughout the season, although research has also illustrated that it protects the plant crown from heat and drought stress, equipment traffic, and disease. This supplemental application of sand is also important to do regularly in order to reduce layering in the thatch profile and maintain good water-infiltration rates. Frequency should depend on turfgrass growth potential but can be done as often as weekly. Timing these applications just prior to rain or a deep irrigation cycle can help incorporate the sand into the canopy and minimize any negative impact on mowing equipment the following day.
Rolling of turf is performed at various intervals primarily to help smooth putting surfaces and increase green speed for daily play or tournaments (Figure 18). Periodic rolling of putting surfaces following mowing can increase putting speeds, allowing for improved ball roll without lowering HOC. By increasing green speed, rolling may reduce mowing frequency and thus the stress of mowing. It can also be used to smooth the surface and remove dew in late or early season periods when little shoot growth is occurring.
In some instances, “target” rolling of greens can provide an ideal putting surface near the hole where it is most beneficial to the golfer with less effort. While most common in the preparation of golf course greens, rolling should also be considered (and is just recently beginning to be more common) on fairways or tees to reduce the occurrence of some turf diseases. As with all cultural practices, rolling should be done under the appropriate field conditions in order to reduce stress. Adequate soil moisture (but not saturation) reduces the potential for compaction.
8.7 Cultural Best Management Practices
Cultivar Selection Best Management Practices
- Select cultivars that are adapted to the desired use, taking note of disease resistance, spring transition traits, and other traits such as shade and wear tolerance.
- Develop and implement strategies, such as hydro-seeding or hydro-mulching, to effectively control sediment, minimize the loss of topsoil, and protect water quality.
Mowing Best Management Practices
- Tall grass should be mowed frequently, and the height should be gradually decreased until desired HOC is achieved.
- In shaded environments, HOC should be increased by at least 30% to improve the health of turf.
- Consider using a PGR as a regular management tool to improve overall turf health for grasses growing in shaded environments.
- Increase HOC during times of stress (such as drought), as much as use will allow, to increase photosynthetic capacity and rooting depth of plants.
- Mowing frequency should increase during periods of rapid growth and decrease during periods of slow growth.
- Vary mowing patterns.
- On greens, change mowing direction every time.
- Reduce clean-up passes at times of stress.
- Utilize equipment maintenance regimes that allow for best possible quality of cut.
- Use reel mowers whenever possible for maintaining turfgrass that requires HOC below 1.5 inches.
- Keep blades of reel and rotary mowers sharp and properly adjusted.
- Return clippings to canopy whenever possible to recycle nutrients and reduce the need for fertilizer inputs.
- Remove or disperse clippings when the amount is so large that it could smother the underlying grass or on golf greens where clippings might affect ball roll.
- Dispose of collected clippings properly; options include composting or dispersing clippings evenly in natural areas.
Aeration Best Management Practices
- Annual core aeration programs should be designed to remove 15% to 20% of the surface area.
- High-traffic areas may require a minimum of two to four core aerations annually.
- Aeration should take into account when weeds are germinating and should be conducted only when grasses are actively growing and not under stress in order to aid in the quick recovery of surface density.
- Aeration events should be as deep as practical to prevent development of compacted layers in the soil profile as a result of cultivation.
- Solid tine aeration should be avoided on wet native soils because it causes compaction and reduction in water movement.
- Backfill holes with new root-zone materials if a drill-and-fill machine is used.
- High pressure water injection can be applied once every 3-4 weeks throughout the summer.
- Venting should be periodically performed to help provide oxygen to root zones, particularly prior to the onset of summer stress. It can also help dry out excessively wet soils.
Surface Cultivation Best Management Practices
- Aggressive or deep vertical mowing should not be used when the turf is growing slowly.
- Shallow vertical mowing and/or brushing could be utilized during the active growing season on putting greens to prevent excessive thatch accumulation.
Topdressing Best Management Practices
- Topdress the playing surface at a rate that will allow the material to be worked into the canopy without burying the plants.
- During favorable weather conditions, light and frequent applications of topdressing sand on putting greens can smooth out minor surface irregularities, aiding in the prevention of thatch accumulation.
- Use only weed-free topdressing materials with a particle size similar to that of the underlying root zone to dilute thatch.
Rolling Best Management Practices
- Utilize rolling for intensely managed turfgrass to reduce stress, mowing needs, and disease pressure.
- To reduce the potential for compaction, do not roll saturated soils.
- To minimize potential for compaction caused by rolling, use lightweight rollers.
- Consider rolling on fairways or tees as well as on greens to reduce mowing frequency and disease pressure.
- Alternate start/stop points on greens to limit wear, changing directions as with mowing.
- Keep roller off of collars except when exiting/entering the green.