Applied in the late fall, pre-emergent herbicides should help prevent winter weeds on skinned areas until the field manager can start dragging in the spring.
Photos courtesy of Pamela Sherratt.

Now is a great time to do a variety of tasks that will prepare athletic fields for 2014. I believe it was Dr. Dave Minner that coined the phrase “putting the field to bed,” and it captures perfectly the idea that there are certain maintenance tasks that can be done right now, just before winter, that will have a tremendous benefit next spring.

Soil cultivation

First off, late fall is a good time to carry out soil cultivation. Fields with holes or undulations in high-traffic areas need renovating at the end of the playing season. Sandy loam or soil material that matches the rootzone needs to be imported and holes filled in. Ideally, the holes should be sodded or covered, because soil left bare over winter is prone to runoff and erosion.

In the fall, soils are typically moist but not yet frozen, and are in prime condition for aeration equipment to move across the field without causing too much surface damage or soil compaction. Aeration equipment opens up the soil surface and allows for gas exchange. In addition, it creates open spaces for seed, fertilizer and topdressing. Scheduling fall coring into the calendar is oftentimes the most challenging part of the process, especially if fields are used until winter. From an agronomic perspective, coring should be done when the turf is actively growing and the likelihood for environmental stress is low. If I had to quantify the ideal period, it would be when the average soil temperature is in the mid-60s. If coring is done when soil temperatures are high, there is a risk of injury to the plant. Conversely, waiting until late fall/early winter when temperatures are cool means that turf recovery (ex. filling in the holes) is slow.

On compacted soils, research on loamy sand has shown that hollow-tine coring (HTC) decreases the soil bulk density and increases air porosity and hydraulic conductivity. The soil strength is decreased with HTC, which may or may not be a desired characteristic. Solid-tine coring (STC) is often a desired practice because it causes less disruption to the turf surface. However, STC is not as effective as HTC with regard to the previously mentioned soil physical properties. HTC decreases the soil bulk density to a greater extent than STC, while air porosity is 19 to 21 percent greater with HTC than STC. Regarding soil macropores, HTC produces a greater percentage of these pores than STC. Hydraulic conductivity is also lower with STC when compared to HTC, while soil strength is greater with STC.

Aeration equipment opens up the soil surface and allows for gas exchange.

Increased root growth from coring in the fall will likely not be observed until late fall or more likely the following spring. It is important to stagger the depth of coring to break or reduce the potential for the development of a compacted soil pan. Coring and removing the core results in no permanent reduction in thatch, but the reincorporation of the cores can help to dilute the thatch layer. In general, coring in combination with other management practices like topdressing will help in thatch management.

Coring during the fall potentially increases the opportunity for annual bluegrass invasion. And recently reported findings out of Penn State University have found that the potential for Poa annua invasion is less when solid tines are used versus hollow tines. A possible reason for this is that with hollow tines the soil brought to the surface also brings Poa annua seeds. This may be an advantage for using solid tines over hollow tines at that time of year.

Seeding and weed control

Any seed applied in the fall will be considered a dormant seed in that it will not germinate until spring 2014. Kentucky bluegrass is an ideal candidate for dormant seeding. Some caution is needed with tall fescue and perennial ryegrass, as they may germinate in warm fall weather, and then be subsequently killed by frost. Bermudagrass also performs relatively well when dormant seeded. In fact, it is better to apply bermudagrass as a dormant seed than risk doing a late summer seeding and losing the sward to winter injury.

A dormant seed typically has a higher mortality rate than a conventional seeding, so 30 to 50 percent more seed is needed. The added advantage of a dormant seed is that seed is in place and ready to germinate, which may give the seed a slight competitive edge over aggressive spring weeds like crabgrass and knotweed.

Table 1: Survey Results of Trinexapac-ethyl Rates used by Sports Turf Managers in the U.S.

The best time to control perennial broadleaf weeds such as dandelion is in the fall, when the plants are storing energy reserves in roots and rhizomes. Herbicides applied at that time are transported downward, killing underground structures as well as the top growth. Warm-season weeds like crabgrass will die at the end of October and may cause problems during the fall renovation if they are too thick, so killing them prior to fall renovations would help. It would also be helpful to have a pre-emergent herbicide ready for late winter (end of February to early March) to prevent weeds that emerge first, namely prostrate knotweed and annual bluegrass. Another use for pre-emergent herbicides is on baseball skins. Applied in the late fall, pre-emergent herbicides should help prevent winter weeds on skinned areas until the field manager can start dragging in the spring. A list of pre-emergent and post- emergent herbicides for both annual and perennial weeds can be found in tables 2 and 3.

Fertilizers in the fall

Fields that are still being used until midwinter are typically fertilized in October and again in November. The November fertilizer application is referred to as late-season fertilizer (LSF) and is made when the grass is still green but top growth has stopped. In other words, the application is made directly after the last mow of the season.

The nitrogen source for LSF is 100 percent quick-release, so that it is rapidly taken up the turf plant. A suitable material (and economically the best) is urea 46-0-0. Field managers that have conducted soil tests and have deficiencies in phosphorus (P) and potassium (K) may look for a blended quick-release fertilizer source that also contains P and K, otherwise 46-0-0 is sufficient. The rate for LSF is 1 to 1.5 pounds of nitrogen (N) per 1,000 square feet. Field managers with sandy soils should apply lower rates to prevent nitrogen from leaching through the sand profile.

Table 2. Pre-emergence herbicides registered for use against annual weedy grasses in turfgrass. Products vary in terms of allowed uses, weeds controlled and turfgrass tolerances. Blue shaded products have both pre and postemergence activity. Always consult the label for specific recommendations prior to use.

The benefits of LSF are well-documented and include: better fall and winter color; earlier spring green-up; increased shoot density; improved fall, winter and spring root growth; and enhanced storage of energy reserves within the turf plant. In particular, signs of spring green-up have been shown to occur two to six weeks earlier if the turf has been fertilized during the previous fall. Most importantly, the enhanced rate of spring greening is realized without stimulating excessive shoot growth that accompanies the early spring nitrogen applications called for in most turf fertility programs.

Ohio State University research found that the spring color of late-season fertilized turf remained quite good until late May or early June, when the effects of nitrogen applied the previous fall began to “wear off.” It has been claimed that late-season fertilization reduces turfgrass cold hardiness and may increase the risk of winter damage by the snow mold diseases, but research has shown that late-season nitrogen applications cause neither problem. Observations over two winters at Ohio State detected no damage caused by either disease or cold injury. However, both types of injury can potentially occur when high nitrogen rates are used and/or applications are not timed properly, resulting in excessive growth going into the late fall or winter.

Spring green-up after using a late-season fertilization (right), and without applying fertilizer (left).

The final step in putting the field to bed is to cover the aeration holes, seed and LSF with topdressing sand. Topdressing sand offers numerous benefits:

  • Most importantly, it fills in undulations and smoothes out playing surfaces. This is paramount for the safety and performance of athletes.
  • Sand is a granular material that can improve finer-textured soils by increasing the macroporosity (large air spaces). Increased macroporosity in turn increases drainage rates and helps to promote deeper root systems, nutrient uptake and gas exchange
  • The topdressing material acts as a cover to conserve moisture and protect the crowns of the turf plant, which is particularly important for bermudagrass.

These aforementioned tasks (aeration, seeding, weed control, fertilizer and topdressing) done together have a much better effect on turf health than when done on their own. These tasks are particularly important on fields that host early spring sports.

Topdressing material acts as a cover to conserve moisture and protect the crowns of the turf plant.

Using PGRs and covers in the fall

Field managers looking for early spring green-up in 2014 might consider applications of trinexapac-ethyl starting in the fall. Trinexapac-ethyl (TE) is a growth regulator that suppresses top growth by ~50 percent, so mowings can be reduced in the fall when the grass is growing quickly. Considerable research with TE has shown that besides growth suppression TE provides: wear and stress tolerance, better color and density, extends the life of painted lines and logos, improved turf performance in shade, and quicker spring green-up.

Table 3. Recommended Herbicides for Broadleaf Weed Control

Our research at Ohio State over the last five years suggests that TE does not adversely affect wear tolerance, recuperative potential, or overseeding and sodding practices with regard to sports field management. More and more sports turf managers are using TE as a standard part of their turf management program. Rates are typically lower than label rate, with more frequent applications. In a recent survey of sports turf managers in the U.S., typical rates were anything from .1 to .5 fluid ounce every two weeks, depending on grass species (see Table 1).

One of the main advantages to using TE is the spring green-up, which is especially important for early spring games like baseball, soccer and lacrosse. In our studies, applications of TE were made on Kentucky bluegrass turf at two rates, .25 and .5 fluid ounce, every two weeks between mid-May and mid-September. The last application in each year was made on September 19, 2007 and September 26, 2008 in Columbus, Ohio. In both 2008 and 2009, spring green-up was significantly quicker, and the turf density and color were significantly improved. Sports turf managers that would like to enhance much quicker spring green-up in 2014 should be making applications of TE now, every two weeks, until the turf stops growing. If fields are not being used this fall, the higher rate might be suggested. If fields are being used, the lower rate is recommended.

In addition to using plant growth regulators for extending fall color and promoting spring green-up, growth covers or turf blankets can offer many advantages to field managers.

  • Significantly quicker spring green-up. Temperatures under the cover can be 6 to 10 degrees warmer than ambient air, so turf growth is two to four weeks quicker than on uncovered turf.
  • Extended fall color. This is particularly important for late fall sports and warm- season grass fields.
  • Speeds up seedling germination and establishment.
  • Holds seed in place and prevents erosion during a rain event.
  • Having the fields covered discourages people from playing on them while they are being renovated.

If the cost is too restrictive for a blanket that covers the whole field, smaller blankets can be used to cover high-traffic areas, such as goalmouths and sidelines. Just be aware that covered areas will be a darker green color than the rest of the field in the early spring. Also beware of snow mold. If you are going to use the grow cover during the winter to protect the turf and speed up growth in the spring, it is very important to put down a snow mold fungicide or a good all-purpose fungicide to prevent any outbreaks under the covers.

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 in turfgrass science at Ohio State University for the last 30 years. Dr. Karl Danneberger has been a turfgrass professor at Ohio State University since 1983. Dave Gardner is an associate professor in the department of horticulture and crop science at The Ohio State University. He teaches courses in turfgrass management, ornamental plant identification and statistics. His research focuses on turfgrass physiology and weed management.