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New England Blade – Mike Goatley, Jr., Ph.D., Professor & Extension Turfgrass Specialist, David McCall, Ph.D., Assistant Professor & Extension Turfgrass Pathologist and Shawn Askew, Ph.D., Professor & Extension Turfgrass Weed Scientist

We’re not forecasting catastrophic weather events (although given the way 2020 has gone, what might happen?) Instead, this article is intended to help you avoid disaster as it relates to the pending storm of what is about to play out on your sports fields. Sports field managers are realizing what is on the horizon regarding the demands for use of their sports fields in 2021 with many fall sports now delayed until the spring. The sports field manager will once again face the reality that every sport is the most important in that particular coach’s, player’s, or parent’s mind and the perception (hopefully not expectation) that field access is unlimited. It was fascinating watching the progression of the ‘MLS is Back’ tournament at the ESPN Wide World of Sports Complex where they hosted 51 matches on 3 fields over 35 days – and the natural grass fields performed marvelously well thanks to an excellent team of sports field managers and consultants. Most of you are facing budget and labor cuts etc. and are quite limited in physical acreage that can be utilized for a greatly expanded spring sports schedule. While there is no guarantee for success, planning and managing for the onslaught of field use in 2021 begins NOW! There are no quick and easy fixes to limitations in soil, a properly crowned field, and an effective irrigation system. So, if those limitations describe your facility, accept that you are somewhat handicapped from the start. However, there are basic cultural, chemical, and communication management concepts that you can employ to help you provide the safest, best playing surfaces under extreme traffic conditions in 2021.

Grow as much as grass as possible until cold weather arrives. 

It doesn’t matter if it’s warm-season or cool-season, now is the time to grow the thickest, densest, healthiest turfgrass possible. Many have had to reduce inputs on fields that were not in use; that was appropriate and even necessary for budgets. But given what is coming, you now need to do everything you can to optimize turf density and health prior to winter because the growth rates of both bermudagrass (4-5 months dormancy) and cool-season grasses (2-3 months of no or restricted growth potential) will decline in a few months.

-Soil pH and nutrient management: The makings of a healthy turf begin with a properly balanced soil in terms of pH and nutrients. A soil test is the only way to really know what the soil needs and there is no cheaper piece of insurance in making informed decisions than to soil test (Figure 1). Both warm and cool-season grasses will benefit from the utilization of a soil test in late summer through mid-fall. There is still time to benefit from nitrogen on bermudagrass fields, but keep the nutrient management standards of up to 1 lb N/1000 sq ft per active growing month in mind, and if possible, go to a light and frequent fertility program as the days get shorter. The strategy for a heavily trafficked sports field in the fall (that carries over to the spring) is to keep the bermudagrass actively growing as long as possible, but not extremely succulent heading into that period when frost/freeze events are expected to occur. One point of caution regarding fertilization on bermudagrass next spring in the midst of all the traffic: the tendency is to want to begin fertilizing as soon as it starts to green in an effort to get as much regrowth as possible. That’s a risky strategy that might pay dividends if Mother Nature cooperates (i.e. no more frost events), but for most locations the threat of late season frosts that can decimate all of that early season growth are enough reason to delay spring fertilization until the possibility of frost has passed (this occurred throughout the mid-Atlantic and mid-South in 2020 when March was warmer than April in many locations). For cool-season grasses, fall is the PRIMARY time to conduct the majority of your seasonal N fertility program for improved performance now and a carry-over in growth and color response into 2021. The standard rule of “if it needs mowing, it is growing” applies to developing your fertility program, with targets of 0.75 to 1 lb soluble N/1000 sq ft per active growing month on our cool season fields.

-Mowing height: This is a double-edged sword question and answer. Mowing your fields at the lower end of a grass’ cutting height tolerance range promotes lateral growth and better density during optimal growing periods (that might be 0.75 to 1.5” for a bermudagrass field, to 1.5 to 2.5” for a cool-season field). Mow the grasses regularly, keeping the 1/3^rd rule in play, but keep in mind that more biomass (to a point… we’re not talking about letting grasses get too tall for the sport) generally equates to better wear tolerance.

-Cultivation: Two thoughts come to mind here. Many have had the opportunity to manage compaction during the down time on their fields, with some afforded opportunities that they never would have had during standard use schedules. Given what is coming with the traffic, compaction relief is especially critical now if it has not been addressed, and perhaps going as far as a linear decompaction treatment or deep tine application is warranted for its long-term benefits that will extend into 2021 (Figure 2)? Then I would suggest you do that this fall if budget permits. There is still time to address compaction on both bermudagrass and cool-season fields during late summer through mid-fall. Then, if time and resources allow, consider how you might be able to incorporate solid tine (or other less surface disruptive tools) into the intensively trafficked areas next spring. You can’t likely do much traditional hollow-tine aeration on a dormant or slowly growing field because the turfgrass can’t recuperate quickly enough to maintain playability. As the spring progresses, you will need to schedule and implement your regular cultivation events to best address soil compaction.

Also, remember that your cultivation programs don’t necessarily have to be on the entire field. The sport results in obvious traffic patterns to address (perhaps one of the biggest challenges will be that due to lack of space, sporting events will be relocated to fields that were previously dedicated to one or two sports. Concentrate your cultivation programs on the trafficked areas if you have budget, equipment, or labor limitations and give them a couple of aeration events rather than poking holes in the best parts of a field that receive little traffic.

-Overseeding: Several sports field managers have indicated that while they did not overseed their bermudagrass the past few years that they thought it likely worth the investment in the seed and the management of the ryegrass in order to have an actively growing grass for all of the mid-late winter traffic. I think that has always been the best argument for overseeding bermudagrass with ryegrass – period. It remains an agronomic fact that the ryegrass is nothing more than a weed to bermudagrass, but intensive spring traffic is a very strong justification for winter overseeding. If you overseed bermudagrass, then OVERSEED your bermudagrass! At least 6-10 lbs of pure living ryegrass seed per 1000 sq ft, and I suggest you go towards the higher side rather than lower to ensure the best density. It will require periodic fertilization, regular mowing, and will be a detriment to your bermudagrass later next spring. However, it might be the best choice for you and your situation. Keep in mind that the ultimate product you seek to provide is a safe field, and clumpy ryegrass has long been one of the biggest reasons to not overseed a bermudagrass field (Figure 3). The debate will continue as to the pros and cons of winter overseeding with the answer to should you or shouldn’t you do it being ‘yes’.

As with fall fertilization on cool-season grasses, fall is also the preferred season to seed and/or renovate cool season turf. Kentucky bluegrass remains a staple of cool-season fields because of its rhizomatous growth habit, perennial ryegrass fits well into cool-season renovation because of how fast it germinates, and the newest generation of turf-type tall fescues continue to expand in use on cool-season turf, especially in combination with Kentucky bluegrass. Dormant seeding of cool season grasses over worn areas will have the seed primed and ready to germinate when spring temperatures and moisture are suitable. For situations where it is critical to get seed up as soon as possible, turf blankets can be applied.

-Use covers if you have them or can afford them. Hopefully your fields will have dense grass cover because of reduced use in 2020, but reality is that a return to practices at some schools and planned fall parks and recreation use schedules, that many fields are likely going to be intensively trafficked even this fall. Turf blankets can enhance late season recovery efforts with seeded cool-season grasses, promote the establishment of overseeded bermudagrass turfs, and protect bermudagrass from damage from winter temperature extremes. Turf blankets will also help keep traffic off of the fields. They are a significant expense, but they are pretty much the only way to stimulate off-season grass growth and development (Figure 4), and if they are properly handled and stored, they will last many years.

Weed control strategies

If procedures for maximizing turf density discussed above are followed, weed control requirements should be less than normal. Use herbicides that have the least injury potential and only target weeds that threaten to dominate the stand or compromise player safety. Avoid using long-residual, preemergence herbicides since expected wear pressure will be “off the charts” as fall and spring games will be combined in the spring. 

Cool-season. Herbicides such as mesotrione, topramezone, triclopyr, halosulfuron, 2,4-D, dicamba, MCPP, and quinclorac should be part of your arsenal. Mesotrione is great for use during seeding to suppress winter annuals without harming cool-season seedlings. It has more residual performance than topramezone in that respect. Topramezone is best for large goosegrass plants, bermudagrass suppression, and general postemergence grass control. Halosulfuron is a safe option to control sedges when new seedlings may be established and grass growth potential must be maximized in a short period of time. Triclopyr should be avoided on turf seedlings or on Kentucky bluegrass during hot weather. On more mature stands, it controls hard-to-kill broadleaf weeds, helps suppress bermudagrass when mixed with topramezone, and reduces white symptoms on weed leaves when used with mesotrione or topramezone. The other broadleaf herbicides are safe options for postemergence control of unwanted broadleaf weeds. Quinclorac is the best product for cleaning up massive crabgrass plants late season.

It should be possible to address annual bluegrass without herbicides. Since fall play is omitted, make every effort to seed heavily and early, fertilize with nitrogen-based products while avoiding phosphorous unless a soil test demands it. Any excess phosphorous will only serve as a starter fertilizer for annual bluegrass. The nitrogen will maximize turf competition with new annual bluegrass seedlings and should reduce their invasion. The key is to get a solid stand of turf before annual bluegrass starts emerging (max. air temps consistently below 70 F) and promote maximum turf density and competitiveness. In addition to avoiding phosphorous, reduce irrigation frequency to match turf needs. Don’t maintain wet surfaces for long periods as this will promote annual bluegrass infestation.

Next spring, only use herbicides that allow for immediate seeding of cool-season turfgrasses as repair of damaged areas will likely be required. For example, don’t delay broadleaf weed control until spring since the products don’t work well in late-winter cold and many of them carry 3-4-week reseeding restrictions. Products like quincorac, mesotrione, and topramezone would be good choices depending on the weed spectrum. 

Warm season. If managing bermudagrass fields, one has a tough decision to make: Overseed or don’t overseed. Repeating what was said earlier, overseeding will arguably place you in better shape for the coming wear stress but be advised that immense effort and resources will be needed this fall to achieve and keep a high-density stand so that it will be ready come February. Be prepared to defend 2-3 mowings per week, fertility expense, fungicides, etc. during a time when no one is on the field. Overseed early and you may need to suppress bermudagrass growth with high rates of trinexapac ethyl and optimize ryegrass emergence with 1/8-inch sand topdressing. Aggressive core aeration or verticutting is not recommended as a means of reducing bermudagrass vigor as this will weaken the bermudagrass substantially for next summer. If coring is needed anyway, that need will trump bermudagrass injury concerns. Thus, if soils are compacted, that is sufficient reason to coincide aeration with the seeding event. In fact, dragging cores can replace the sand top dressing as a means to promote ryegrass establishment in a dense bermudagrass stand. If overseeding at higher rates, early, and a successful stand establishment is gained, weed control inputs may not be needed. If you must overseed later or annual bluegrass has already started to emerge prior to overseeding, apply foramsulfuron one week prior to seeding to kill emerged annual bluegrass.

The counter argument in favor of not overseeding best applies to fields that are entering the fall season at above-average density. In fact, any or all of the following may make non-overseeded bermudagrass fields a prudent choice: If your bermudagrass density is high, you have limited budget, if you can reduce the number of events played on any one field, or if you expect the field to be “blown up” regardless of what you do. When not overseeding, resources may essentially be held back and used for the recovery phase rather than for producing an optimal stand of perennial ryegrass in advance of the coming spring. The downside is that your only option when playing conditions become unsafe may be to close the field. Sand top dressing and divot fill can improve field safety but is a short-term fix when turf density is lost. Weed control needs will increase on non-overseeded fields. Expect to use glyphosate or glufosinate to control winter weeds after the field enters dormancy (Figure 5). Since this often happens in February, you may be too close to the deferred season to clean up the fields. It is best to target winter broadleaf weeds with 3-way combo products the previous fall. Likewise, products like trifloxysulfuron applied in fall as bermudagrass is entering dormancy can help knock back winter weeds and allow for a glyphosate or glufosinate follow up to be more effective and aesthetically pleasing in late February.

Disease control strategies

Diseases will likely impact sports fields next spring, whether managing warm-season or cool-season grasses. As previously mentioned, improving the overall density, uniformity, and vigor in the fall will pay dividends next spring when traffic is at an all-time high. Following the advice on each of the cultural practices listed above will not only improve the appearance of the field, but will also allow the plants to defend themselves against turfgrass pathogens.

Spring dead spot continues to be the most prevalent disease on bermudagrass sports fields (Figure 6). If no actions are taken this fall, the only viable option will be to promote recovery in the spring through nitrogen fertilization and cultivation. The problem that we will likely run into next spring is that turfgrass managers will be attempting to do this without any breaks from foot traffic on the fields, something that will prove almost impossible. Both fall fertilization and mowing height can impact spring dead spot the following year.

As previously mentioned, applying small amounts of nitrogen into the fall will extend the photosynthetic period of the bermudagrass, resulting in a healthier root system to fight off the spring dead spot pathogen during the winter. However, be cautious not to overapply as too much top growth late into the season can be detrimental to the root system as well. Also pay attention to any macro- or micronutrient deficiencies that may show up during the soil test and supplement accordingly. As for mowing height, bermudagrass is less susceptible to cold injury when mowing heights are increased as the stand enters winter dormancy. The end result of spring dead spot damage is caused by localized winterkill in patches that are weakened by the pathogen. We suggest slowly stepping up the mowing height by approximately 50% as the grass slows down. For example, if fields are maintained at 0.75” during the active season, consider raising to somewhere between 1” and 1.25” during the last couple months of fall growth.

If spring dead spot has historically plagued a particular sports field, this may be the year to strongly consider applying a preventative fungicide. Several fungicides have proven effective. The most consistent performers in Virginia Tech research trials have been the SDHI class; such as isofetamid (Kabuto), penthiopyrad (Velista), and pydiflumetofen (Posterity). Fungicides should be applied in the fall when soil temperatures fall between 70°F and 75°F. A repeat application approximately 3-4 weeks later may prove beneficial if we experience a long, gradual decline in soil temperatures. Fungicide applications for suppressing spring dead spot should be watered in immediately to maximize their performance.

Those needing to overseed their fields this fall with a cool-season grass should be wary of seedling diseases that can quickly wipe out a stand of new grass. Particularly, be cautious of gray leaf spot and ‘damping off’ during the first couple of weeks after seeding. Gray leaf spot, in particular, has become increasingly problematic on both perennial ryegrass and tall fescue in late summer to early fall. Both diseases are most severe during prolonged periods of leaf wetness in conjunction with high canopy temperatures. However, consistent moisture drives each disease more than temperature. And, both diseases are also most severe when nitrogen is readily available. Consistently wet with plenty of readily available nitrogen describes establishment to a T, as seed needs to be watered continuously for the first couple of weeks, typically in conjunction with a starter fertilizer. The potential for these diseases shouldn’t prevent fall overseeding to prepare for next spring. Rather, extra caution should be taken to inspect the seedlings routinely to any symptoms of the diseases or, more importantly, signs of the pathogens. As with spring dead spot, this may be a year where it is worth the investment in a good fungicide to make sure overseeding establishment is a success.

Establishing and maintaining communication is more important than ever

This article likely doesn’t do as much for you as it could your supervisors, administration, players, coaches, etc., so you might accidentally leave it in a place where they might take a glance at it! Even with all of the agronomic and pest management challenges detailed, the toughest part of your battle in sports field disaster prevention is always the management of the traffic on the field. You aren’t likely to win many of these battles, but it doesn’t mean you shouldn’t wage the battle because two-way communication is always an important part of any successful operation. Regular communication with your coaches, administration, and players regarding upcoming field use schedules begins now as you plan for what is likely to happen beginning in early 2021. Getting buy-in from them regarding at least a basic understanding of the pending challenges is an important first step in your management program. Plainly stated, excessive traffic leads to compaction and compaction leads to the loss of grass because of a lack of oxygen and physical limitation to root penetration. Remember that one traffic event on a saturated soil in any season can likely destroy a season’s worth of efforts in providing a safe playable field; the magnitude of the damage is much greater if a wet field is trafficked over the late fall to early winter months when there is neither time nor conditions to adequately promote recovery. Fields exist to be used, but ensure that everyone is on the same page when it comes to understanding that field use guidelines and practices must ensure that athlete safety comes first.