Editor’s note: This article originally appeared in the June 2013 issue of SportsField Management.
Warm-season turf species like bermudagrass grow best at soil surface temperatures from 80 to 95 degrees Fahrenheit, but they can be established as soon as soil temperatures reach 50 degrees Fahrenheit. Bermudagrass establishment by seed or sprigs is typically carried out in April or May, but no later than June, so that it is mature enough by fall to withstand traffic, wear and the onset of frost. However, it is also OK to establish bermudagrass by seed, sprigs, stolons, plugs or sod during the early summer months as long as there is an available water supply.
Cool-season turfgrasses like Kentucky bluegrass, perennial ryegrass and tall fescue do best between soil temperatures of 50 and 65 degrees Fahrenheit, and they can get severely stressed during the summer months. The ideal time to do any kind of renovation on cool-season turf is early fall (August to September) when soils are warm, there is a good chance of rain, and weed pressure is low.
However, in many cases, fields are used February through May, and then there is some downtime in June and July before fall sports resume in August. Renovating fields in June and July is far from ideal if using cool-season turf due to the hot, dry weather and pressure from weeds like crabgrass, goosegrass and nutsedge. These factors can make it almost impossible to get cool-season grasses established, especially slow-growing species like Kentucky bluegrass. With that said, if there is time to renovate and, more importantly, someone available to nurture the newly established turf, it is possible to renovate successfully in summer if certain tasks are undertaken.
Preparing soil prior to planting seed or sod is key for a successful renovation project, and there are several steps to the process.
First, conduct a soil test to determine if there are nutrient deficiencies or corrections to be made with soil pH and/or organic matter content. Follow recommendations from the lab in relation to fertilizer rate and frequency.
If you’re doing a total renovation, kill the existing vegetation with a nonselective herbicide and remove as much plant material/organic matter as possible by close mowing, scarifying and removing debris from the site. The type of seedbed preparation will then be determined by the quality of the soil, whether it needs improving or not.
If the soil is poor quality or the field needs to be regraded, till the soil to a depth of 4 to 6 inches and remove deleterious material like rocks and glass. The extent to which the soil is remedied or amended will depend upon the soil test, desired soil quality and budget. The goal is to maximize drainage and root growth, so ideally the soil should contain at least 75 percent by weight sand and greater than 5 percent organic matter. At the very least, tilling in 1 to 2 inches of an organic matter material like compost will help to improve soil properties.
A seedbed tilled during the summer months without Tenacity resulted in greater than 90 percent weed cover, namely crabgrass, yellow nutsedge and goosegrass.
PHOTOS BY PAMELA SHERRATT.
Total renovation offers an opportunity to install drainage tile and irrigation pipe, as well as reestablish proper grades. Since weed pressure is so great in the summer, it’s important to treat the seedbed with an herbicide that won’t affect germination of the grass seed. Examples of herbicides for cool-season turf would be Tenacity (mesotrione) or SquareOne (quinclorac and carfentrazone).
In our research, applications of Tenacity resulted in a clean, weed-free seedbed. A seedbed tilled during the summer months without Tenacity resulted in greater than 90 percent weed cover, namely crabgrass, yellow nutsedge and goosegrass (Figure 1). Research from The University of Wisconsin (Pease & Stier) has also shown that Tenacity can be added to a hydromulch slurry to prevent and control grassy and broadleaf weeds. The hydromulch slurry (seed plus fertilizer plus pulp) already offers a way to conserve moisture, and adding a weed control allows for better turfgrass establishment.
If the soil does not need amending or grading, then don’t till it, as tilling will bring weed seeds up to the surface. Avoiding soil disturbance during the late spring and summer months will prevent aggressive weeds like crabgrass and annual bluegrass from taking over.
Prior to seeding, a heavy-duty scarifier can be used to create shallow slits and grooves on the soil surface so good seed-to-soil contact is achieved. Alternatively, a slit seeder will place the seed directly into the soil surface. Research at Ohio State University (OSU) has shown that this particular seedbed preparation, with minimal soil disturbance, results in less than 30 percent weed cover, which is easily controlled with a postemergence herbicide once the new grass seedlings are mature enough that they have been mowed three times. The conclusion here as far as soil disturbance is twofold: try not to disturb the soil and bring weed seeds to the surface; and if the soil is disturbed, use an herbicide at the time of seeding to prevent weed seed germination.
If total renovation is not needed, then overseeding can improve the turf stand. Thin turf or worn areas on the field are remedied by removing thatch and other surface organic matter with a scarifier/dethatcher or a device like the Koro TopMaker, and then slit seeding diagonally in two directions.
Seed, sprig and sod selection and rates
There are many varieties of cool-season grasses: Kentucky bluegrass (Poa pratensis), perennial ryegrass (Lolium perenne) and turf-type tall fescue (Festuca arundiancea). The National Turfgrass Evaluation Program is a good source for information on each variety, as is a local turfgrass seed supplier. Seed rates for cool-season turf are as follows: Kentucky bluegrass at 1 to 3 pounds of seed per 1,000 square feet, and perennial ryegrass and tall fescue at 6 to 8 pounds of seed per 1,000 square feet.
Some rules of thumb when applying seed during the summer would include:
- Choosing seed that has shown greater resistance to summer diseases like Pythium blight, brown patch, dollar spot and grey leaf spot.
- Increasing sward diversity by including three to five cultivars.
- Using seed coated with fungicide (“Apron” treated), especially on perennial ryegrass seed.
- Sticking to the seed rate. Excessive seed rates will result in crowded, weak plants that are more susceptible to traffic and disease problems.
Several varieties of bermudagrass (‘Riviera’, ‘Sunsport’, ‘Veracruz’, ‘Yukon’), centipedegrass (‘TifBlair’) and zoysia (‘Zenith’) produce viable seeds that can be planted from mid-May to early July, no later than 90 days prior to the first fall frost. The recommended planting rate of hulled bermudagrass seed is 1 pound per 1,000 square feet. Centipedegrass should be seeded at the rate of .5 to 1 pound per 1,000 square feet, and 1 to 2 pounds of zoysia seed is recommended per 1,000 square feet.
Sod, sprigs and plugs of vegetatively established varieties of hybrid bermudagrass (‘Tifton 419’, ‘TifSport’, ‘Quickstand’) and zoysia (‘El Toro’, ‘Meyer’, ‘Palisades’) are also available. Bermudagrass and zoysia sprigs are sold by the bushel, with 1 square yard of sod representing one Georgia bushel of sprigs, and one Texas bushel of sprigs equal to a volume of 1.24 cubic feet. A Georgia bushel is occasionally referred to as an industry standard bushel (ISB).
Sprigs are usually broadcast over an area at the rate of 200 to 400 or more bushels per acre, or 5 to 10 or more bushels per 1,000 square feet before being pressed into the soil. Plugs are usually planted 12 or 24 inches on center. A machete can be used to cut sod into plugs. More than 300 2-by-2-inch plugs can be cut from a square yard of sod.
Unlike sod and plugs, which can be irrigated deeply and less often, newly sprigged turf should be kept moist by irrigating lightly and frequently each day. As sprigs produce leaves and a fibrous root system, more water can be applied less often on an as-needed basis (e.g., .5 inch of water when soil is dry). Sod and plugs are usually anchored in soil by three to six weeks after planting. The root systems of seedlings and sprigs might take a little longer to develop.
The alternative to establishing turf by seed or sprigs is to use sod. Sod gives instant turf cover, and it also offers field managers a great way to quickly get a more desirable sward back onto the playing surface.
Sod installation and care
Preparation of the soil is exactly the same for sod installation as it is for seeding. The end goal is to have a seedbed clear of deleterious material and weeds, and the soil tilth should be firm but not compacted. A granular starter fertilizer should be applied to the soil at 1 pound of nitrogen per 1,000 square feet before the sod is installed.
The sod should be mature enough that it holds together well (one to two years old), but not so old that is has excessive thatch. Ideally, the sod would have been maintained at the sod farm at the same level it will be maintained at its new destination. So, if the sod will be used on a high-profile soccer field and maintained at a height of 1 inch, it should have been maintained at a 1-inch height at the sod farm. In reality, the sod usually comes in with a longer sward height and must be brought down to the desired height through good mowing and topdressing practices.
Sod is laid in a staggered, brick-like pattern to prevent long seams and maximize stability.
Sod used on athletic fields should not have any net backing. The netting helps to keep the sod together during transport and installation, but if it ends up on the field and the sod gets worn away, it is easy for athletes to get their cleats tangled up in it.
The sod should be monitored closely during the installation process, with each sod roll undergoing strict quality control to make sure it: has a healthy root system; has not been damaged by heat buildup during transport, though most sod suppliers will transport in coolers if the journey is long; and is weed, pest and disease free. While it is an uncomfortable experience to have to decline sod and send it back to the farm it does happen, so be prepared to have a backup plan in place.
Sod should be installed immediately upon arrival to prevent heat stress. It is laid in a staggered, brick-like pattern to prevent long seams and maximize stability. Ideally, seams are then topdressed with good-quality topsoil or sand to make sure they are tight together and not vulnerable to drying out.
Directly after installation, the sod should be lightly rolled to ensure good sod-to-soil contact. Never roll drought or heat-stressed sod, as that will cause tissue injury. The sod should be irrigated heavily at first, and then moderately, several times a day for the first week to 10 days so the seams don’t dry out.
Newly seeded perennial ryegrass turf that was treated with granular Subdue Maxx (mefenoxam) fungicide at the time of seeding showed improved color, density, biomass, sward height and overall establishment quality compared to untreated perennial ryegrass.
As soon as the sod has firmly rooted, which may take two to six weeks, it should be aerated. Solid or core aerification through the sod layer in conjunction with topdressing helps to create open channels of homogenous material from the playing surface to the underlying soil. If those channels are not opened up regularly, the sod layer can create problems. Most importantly, the sod layer inhibits drainage, which leads to shallow-rooted turf and poor playing conditions. It is common to see sod decline rapidly the second year after installation if it has not been cored and topdressed regularly during the first season.
Seeding and post-seeding care
Once the seedbed is prepared it’s time to seed. A slit seeder is ideal, as it places the seed directly into the soil surface. Slit seeding diagonally in two directions ensures uniform seed distribution and prevents the turf from establishing in stripes. It is important to check the seed hopper to ensure there’s enough seed, since the operator stands at the back of the machine and cannot see the seed dropping out the hopper. This sounds like such an obvious suggestion that it doesn’t warrant saying, but it happens.
For grass seed to germinate it needs moisture, oxygen and soil temps above 50 degrees Fahrenheit. Moisture is the key. If there is moisture stress or drought during early germination, when the seed is taking on moisture and the tissues swell (imbibition), then it may not damage or kill the embryo. However, if there is drought stress during the later stage of germination, when there is cell division and growth, then the seed is more likely to die. So it’s critical that the seed stay moist until green grass cover is visible. With fast-germinating turf species like annual and perennial ryegrass, the germination period is around three to five days, tall fescue is about seven days, and Kentucky bluegrass germinates in seven to 21 days, depending on the variety.
In 2009, granular Heritage and Subdue Maxx were applied at the time of seeding. Results were similar to those seen in 2008 in that fungicide-treated turf provided better quality and quicker establishment. However, midway through the study untreated and Subdue treated turf became infected with rust disease. The turf treated with Heritage was not affected by rust.
Keeping the seed in a constant state of moisture until green tissue is visible requires syringing the seed several times daily. There is no hard and fast timing on the amount of syringing cycles needed, as it depends on daily weather conditions. On sunny, windy days, with a high evapotranspiration (ET) rate, seed may need syringing as much as five times per day, while on cloudy, calm days (low ET rate) seed may only need to be syringed three times per day.
An example of a syringing cycle could be: 9 and 11 a.m., and 1, 3 and 5 p.m. During late June, July and August when there are more daylight hours, a 7 p.m. cycle may also be required. Syringing is not the act of replenishing water lost through ET, or applying water deeply and infrequently to encourage growth. Syringing is a light application made purely to wet the seed. Syringing is done either by a quick rotation of an irrigation head (with an inground/pop-up automated irrigation system) or by hand. Syringing by hand is a common practice and involves light watering with a hose equipped with a syringing nozzle. The purpose of syringing is to lightly wet the seed, not blast it off the soil surface, so a syringing nozzle on the end of the hose is essential.
As mentioned previously, a starter fertilizer is applied with the seed, and repeat applications of starter or maintenance fertilizer are an important part of the renovation process. Typical rates would be .75 to 1 pound of nitrogen per 1,000 square feet per calendar month until there is 100 percent sward density. Some field managers prefer lighter, more frequent rates of .5 pound of nitrogen every two weeks.
To prevent seed movement and soil erosion after a heavy rain, the seed and fertilizer should be lightly covered with topdressing sand, a growth blanket, hydromulch or straw. A cover helps to retain moisture and heat, and prevents seed and soil movement until the seedlings are established. It might also deter field users from using the area until the renovation is complete.
Applying starter fertilizer and water so liberally in summer will increase the newly seeded areas susceptibility to diseases like Pythium blight and brown patch. A preventative approach is to use fungicide-coated or “Apron” treated seed and to apply a liquid or granular fungicide at the time of seeding. It is crucial to have a fungicide program planned if renovation is taking place over the summer, when environmental conditions are favorable for disease. There are several fungicide families that target Pythium blight and brown patch, and they should be rotated to discourage fungicide resistance. A fact sheet called “Families of Fungicides for Turfgrass” can be found at www.turfdisease.osu.edu.
The fungicide effect
During previous studies at OSU, there has been some evidence to suggest that fungicides could have a beneficial, nontarget effect on turf health, particularly during the summer establishment period. In 2008, newly seeded perennial ryegrass turf that was treated with granular Subdue Maxx (mefenoxam) fungicide at the time of seeding showed improved color, density, biomass, sward height and overall establishment quality compared to untreated perennial ryegrass. The Subdue treated turf also contained greater (.5 percent) tissue nitrogen compared to the nontreated turf. Neither of the grasses showed symptoms of disease, so the fungicide appeared to have a nontarget effect on turf health (Figure 3).
In 2009, both granular Heritage (azoxystrobin) and granular Subdue Maxx were applied at the time of seeding. Results were similar to those seen in 2008 in that fungicide-treated turf provided better quality and quicker establishment. Midway through the study however, the untreated and Subdue treated turf became infected with rust disease, so the nontarget effect was lost. The turf treated with Heritage was not affected by rust.
While it is challenging to establish turf during the summer months, it is not impossible. A good seedbed is critical, as is irrigation and fertilizer. What is also important for summer renovation that may not be as critical in the fall is a sound fungicide and herbicide program, because the pressure from weeds and disease is so high.
Author’s note: Thank you to Dr. John Sorochan at The University of Tennessee Knoxville for kind permission to use some text on bermudagrass establishment.
Pam Sherratt is a sports turf specialist at Ohio State University and served on the STMA board of directors from 2010-2011. Dr. John Street has been a professor of turfgrass science at Ohio State University for the last 30 years.