1. Soil compaction (high bulk density) is by far the most common and problematic issue on sports fields. Soil compaction is caused by an increase in soil bulk density attributed to foot traffic. Problems associated with soil compaction include an increase in surface hardness, ball roll and bounce; poor growing conditions for turfgrasses; and inadequate drainage.
Maintaining 100 percent desirable grass cover is the crux of preventing soil compaction, since the maintenance practices needed to grow healthy turf also include routine and effective soil cultivation. A strong soil cultivation program with solid tines used during the playing season and the more disruptive machines (core aerifiers, verti-drains, etc.) used out of season will help keep the playing surface open. If soil compaction is routinely a problem, mechanical cultivation alone may not be sufficient, and soil amendment with sand or compost may be needed).
2. A field’s grade is the underlying factor that dictates the success or failure of the playing surface, since poor grades cause major problems with puddles and soil erosion. The problems caused by poor grades not only lead to poor growing conditions for turf, but also lead to soil compaction issues and commonly to canceled games and loss of revenue.
Poor grade on baseball infield.
A crown on a native soil field or a sloped grade on a baseball field influence how quickly water and soil move from the surface during a rain event. Excessive/high grades result in quick water movement, but can also result in soil erosion, particularly on skinned infields. Conversely, a flat or undulated grade results in very slow water movement and puddling. Sand-based field drainage rates are not as reliant on surface runoff, since infiltration rates are high, and grades may range from virtually flat to 0.5 percent slope. On native soil fields, where infiltration rates are low, runoff is more important and higher grades of 1 to 2 percent are installed.
On baseball infields the grade is critical, since infiltration rates are extremely slow, but there is no turf cover to hold the infield soil mix in place. Even the smallest failure in grade can lead to standing water. For that reason it’s important that the majority of any renovation budget be invested in good grading, because getting the grade wrong results in a field that will never drain. A grade of 0.25 to 0.5 percent slope is common on skinned infields, with the pitcher’s mound the highest point and all slopes running from it to the back and sides. Outfields have a great slope of 1 percent. Higher grades on the infield would facilitate faster water movement, but would also result in much greater movement of the infield mix, with it migrating into the surrounding turf and creating lip problems.
One final point on the subject of grades is that water doesn’t flow upward, so any kind of hole or undulation – outside a turtle-back crown on a football field, a depressed soccer goalmouth, a lip on a baseball field, etc. – will trap water and create puddles. The slop and grade are critical during the building phase, but the annual upkeep of surface evenness through filling in holes, topdressing and divoting is also important. Having an infield laser-graded every couple of years is also a good idea.
3. Inadequate drainage is the curse of many native soil fields. It’s not uncommon to see infiltration rates as low as 0.01 inch per hour on soil fields, especially if a strong soil cultivation and topdressing program is not in place.
Ideally, a field should yield saturated hydraulic conductivity values of 1 to 2 inches per hour, which is a recommended minimum permeability for high-traffic athletic fields. This goal is achieved by establishing sufficiently high sand contents in the rootzone, typically ~75 percent by weight. The increase in sand results in 15 percent of the total pore volume composed of larger-sized pores (> 0.05-mm), which are responsible for rapid air and water movement. A soil should contain at least 10 to 20 percent of these macropores to allow adequate infiltration, drainage and gas exchange.
Soil modification with sand is performed in a variety of ways: blending the entire rootzone on or off-site, installing sand slits/bands into the existing native soil, installing a sand cap, or topdressing with sand each year as part of the annual maintenance program. Adding organic material like bulky compost to soils that are devoid of organic matter is also an option. Composts reduce the bulk density of a soil and increase the nutrient status and water-holding capacity, but applications should be made thoughtfully and in conjunction with careful monitoring of infiltration rates.
4. Most sports fields need some kind of supplemental irrigation to get them through dry spells or periods of intense use. Even fields located in parts of the U.S. that get up to 40 inches of rainfall each year can still have spells six to eight weeks long during the summer with no rainfall. Fields that are underwatered cannot recover from sports traffic or provide the right environment for growing grass. They can also be hard and unforgiving on athletes. Supplemental irrigation is therefore important and is used to:
- Maintain turf growth and recovery.
- Encourage new seeds, sprigs, plugs and sod.
- Lower canopy temperatures during intense heat stress.
- Water-in fertilizers and pest control products.
- Soften hard and compacted surface playing conditions on native soil fields.
- Produce firm, fast playing surfaces on sand fields.
- Control dust on baseball and softball fields.
There are several approaches to conserving water on fields, starting with turfgrass selection. Bermudagrass is a C4 grass that has relatively low water use rates. Of the C3 grasses used for sports, tall fescue is the most drought-tolerant and is adapted to the transition and cool-season zones. Other moisture conservation options include using growth blankets, applying wetting agents, raising mowing heights, and applying irrigation early in the morning. An accepted integrated pest management (IPM) tactic when applying irrigation to turf is to replace the water lost through evapotranspiration with a “deep and infrequent” approach to timing. If an inground irrigation system in not economically viable, rain trains or water cannons are an option. In many situations, fields with an inground irrigation system are watered too much, causing agronomic problems and increased costs.
5. Annual bluegrass (Poa annua) is one of the top five most widely distributed plants in the world. It is ubiquitous. Unfortunately, annual bluegrass’ shallow roots, light green color, and sensitivity to heat and drought make it unsuitable for sports field use. Environmental conditions that favor annual bluegrass growth include compacted soils, moist soils, low mowing heights and moderate to high fertilizer use. Cultural control includes handpicking, avoiding soil disturbance (i.e. core cultivation) during peak germination in the fall, judicious use of water and fertilizer and regular overseeding with desirable grasses. Chemical control options are being studied by Dr. John Street at Ohio State University (OSU). His preliminary results are summarized in Table 1.
6. Prostrate knotweed (Polygonum aviculare) is a broadleaf, laterally spreading weed that can quickly take over a sports field. It is a summer annual weed that germinates very early in the season (March in Ohio) and is sometimes mistaken for crabgrass when it first emerges.
The predominant environmental condition that favors prostrate knotweed growth over desirable grasses is soil compaction, so it is seen frequently in high-traffic areas of the field. A cultural approach to prostrate knotweed control would be to perform regular soil cultivation to relieve bulk density and to aggressively overseed, sprig or sod to maintain 100 percent grass cover.
Prostrate knotweed can be prevented with the application of a preemergence herbicide prior to seedling emergence, before soil temperatures are consistently in the mid-40 degree Fahrenheit range. The most effective preemergence herbicides persist for quite some time (~12 weeks) in the soil, which could push back any kind of seeding operation until June or July. A postemergence approach using a broadleaf herbicide containing dicamba would effectively control prostrate knotweed, and there would only be a three to four-week waiting period before reestablishing new turf.
7. Summer diseases like brown patch (Rhizoctonia solani) and Pythium (Pythium spp.) continue to cause problems on cool-season turf during hot and humid weather conditions. Applying fertilizer and water liberally in summer will significantly increase the likelihood of newly established areas getting diseases like Pythium blight and brown patch. A preventative approach is to either use fungicide-coated or Apron-treated seed, or to apply a liquid or granular fungicide at the time of seeding. It is crucial to have a fungicide program if renovation is taking place over the summer, because environmental conditions are so favorable for disease to occur.
Summer diseases including Pythium blight
Fields that contain an appreciable amount of perennial ryegrass are more susceptible to summer diseases, and tall fescue fields need to be watered and fertilized carefully to avoid brown patch. There are several cultivars of both species that show improved resistance to summer diseases. Lists of those cultivars are available on the National Turfgrass Evaluation Program website (http://www.ntep.org).
There are several fungicide families that target Pythium blight and brown patch, and they should be rotated to discourage fungicide resistance. A factsheet, “Families of Fungicides for Turfgrass,” can be downloaded free from the OSU Turfgrass Disease Team website at: http://www.turfdisease.osu.edu.
8. Gray leaf spot, caused by the pathogen Pyricularia grisea (Magnaporthe grisea) is a serious disease of both cool and warm-season turfgrasses. Under optimal environmental conditions and on susceptible hosts, small leaf spots quickly turn into water-soaked lesions, which rapidly coalesce together and progress to twisted necrotic leaf tips. If left unchecked, the disease moves rapidly to other susceptible plants.
The overall appearance often resembles severe drought stress, but if soil moisture is checked, the test will show that the soil has adequate water. Severe outbreaks look as if the turfgrass was scorched with a flamethrower. The onset of gray leaf spot has been described as a general chlorosis of the sward followed by a rapid blighting of the entire plant. This is an unforgiving disease.
Gray leaf spot
Cultural approaches to controlling gray leaf spot include choosing cultivars with improved genetic resistance , and being careful with irrigation and fertilizer applications during times that are most favorable for the disease to occur. Since duration of leaf wetness is a contributing factor in the development of the disease, early morning mowing or brushing to remove dew, improving air circulation with portable fans, and careful use of plastic rain tarps are all important factors.
Fungicides are important for gray leaf spot control on sports fields, particularly high-profile game fields with a lot of perennial ryegrass on them. Fungicide applications should begin prior to the onset of disease and continue every one to three weeks as needed when warm, humid weather prevails. The extent of disease pressure will greatly influence fungicide performance. If gray leaf spot outbreaks are in an advanced state by the time fungicide sprays are initiated, it is likely that levels of control will be unacceptable. Fungicide-resistant strains of the pathogen have been identified. Fungicide selection should be guided by a sound resistance-management strategy.
9. Spring dead spot (Ophiosphaerella korrae and O. herpotricha) on bermudagrass first appears as circular patches of grass that do not come out of winter dormancy. These patches then collapse and leave sunken areas of dead turf that adversely affect the safety and playability of fields.
Spring dead spot is a disease that attacks the roots and rhizomes of bermudagrass turf, therefore any remediation work done in early spring needs to be carefully administered so as not to further stress the turf. Practices such as aggressive verticutting should be avoided in order to give the turf time to recover its root system.
Spring dead spot
Another problem that may occur with bermudagrass during early green-up is root dieback. This phenomenon, first discovered by Texas A&M in the late ’70s, describes a process whereby the root system will die rapidly, sometimes over a period of 24 hours. Loss of the root system through dieback or spring dead spot adversely affects the turf’s ability to establish in the spring and also makes that turf prone to biotic and abiotic stresses.
An IPM approach to managing spring dead spot includes:
- Choosing bermudagrass cultivars with improved resistance. Since winter-hardiness of bermudagrass is directly related to its susceptibility, it’s not surprising that the most cold-tolerant bermudagrass cultivars are better at resisting damage. A list of cold-tolerant cultivars can be found at the National Turfgrass Evaluation Program website.
- Maximizing soil health by alleviating soil compaction, improving soil drainage, controlling thatch and maintaining a soil pH under 7.0 (ideally 5.5-6.0).
- Providing the turf with light applications of nitrogen in the fall (no more than 0.5 pound/M after mid-September) and two fall applications of potassium, which has been shown to reduce spring dead spot damage. Recovery the following spring should be encouraged by light and frequent irrigation and soil cultivation, not by heavy applications of nitrogen, since that will encourage top growth and not root recovery.
- Controlling spring dead spot with preventative fungicides requires patience, as it may take several years. It is also critical to have a clear understanding of fungicide type, timing and application method.
10. White grubs and billbug larvae can be problematic on sports fields during the summer months, especially during drought conditions. In some instances, the symptoms of billbug or white grub attack can be misdiagnosed as drought, but there are easy identification tests, such as the tug test for billbugs, or checking the thatch-to-soil interface for white grubs (see Dr. David Shetlar’s website for instructional videos of both at http://www.entomology.osu.edu).
If bluegrass billbugs are a consistent nuisance, it might be a good idea to grow different grasses on the field. For example, tall fescue contains endophytes that eliminate surface-feeding insect problems. If white grubs are an issue, thatch control is key, as is growing turf with deep, healthy roots, since grubs chew through the roots as they consume organic matter.
White grubs and billbugs
Wait until these pests have been confirmed to be present before utilizing a chemical approach (as evidenced by damage last year). Once confirmed, make an application of clothianidin (Arena) in mid-May to control both for the season. Stay away from the pyrethroid insecticides because of skin sensitivity issues. A rescue treatment for white grubs can be made with products containing trichlorfon (Dylox), but keep people off the field for 24 hours after the application.
Pam Sherratt is a sports turf specialist at Ohio State University and served on the STMA board of directors from 2010-2011.