Cover Story

The Good, the Bad, and the Ugly of Fraise Mowing Sports Fields

By Ray McCauley and Grady Miller, NC State University

Bermudagrass is the turfgrass of choice for sports fields in North Carolina because of its excellent quality, stress tolerances, and rapid growth rate. However, bermudagrass can produce an excessive thatch layer (>0.5-inch depth) that can disrupt turfgrass health and aesthetics, as well as sports field behavior. Specifically, excessive thatch reduces drought tolerance, increases localized dry spot potential, and slows water, air, fertilizer, and pesticide movement into the soil. Excess thatch also increases the likelihood of winterkill and disease- especially spring dead spot.

Sports field managers often employ topdressing, vertical mowing, and/or hollow-tine aerification to manage thatch. Topdressing, the broadcasting of a thin layer of sand or soil across the field, is the best cultural practice for controlling thatch accumulation (Beard, 1973; Miller, 2008). However, topdressing must be performed multiple times annually to be effective. If thatch levels become excessive, mechanical practices must be used. Hollow-tine aerification and vertical mowing have been the standard practices used to manage thatch. Although their aggressiveness may be adjusted, multiple years of vertical mowing and hollow-tine aerification are often necessary to effectively manage thatch.

Fig.1 Fraise mowing affects 100% of a field’s surface.

Fraise (fraze) Mowing – The Good

Fraise mowers come as large (4 to 8’ wide) tractor-mounted or small (~2’), self-propelled units. All fraise mowers have blades attached to a vertically rotating cylinder that removes 100% of the surface to depths of 0 to 2 inches. Fraise mowing enables sports field managers to (potentially) remove all thatch without the added time and expenses of gradual thatch reduction. What would have taken years to do with periodic vertical mowing, hollow-tine aerification, and/or topdressing can now be done in an afternoon with a fraise mower. A single vertical mowing or aerification event impacts ≤ 31% of a field’s surface area and leaves most of the thatch layer intact (McCarty & Miller, 2002). Fraise mowing impacts 100% of the surface and can remove all thatch to two-inch depths. These numbers demonstrate the efficacy of fraise mowing to remove thatchespecially compared to standard cultural practices.

Fig. 2 Fraise mowing enables total thatch removal.

Ongoing research at NC State is evaluating the longevity of fraise mowing at 0.25 and 0.5 inch depths on thatch reduction. The thatch reducing benefits of fraise mowing at 0.5 inch depth lasted for >1 year. Fraise mowing at 0.25 inch decreased thatch content for ≤1 year. These Initial results suggest that fraise mowing at 0.5 inches should be performed at three-year intervals for optimal thatch control. Meanwhile, fraise mowing at 0.25 inches should be performed annually.

Fig. 3 Fraise mowing produces a lot of debris.

Thatch affects the behavior of sports fields- especially field firmness. Thatch makes fields softer and slower. Athletes must exert extra energy and tire faster on thatchy fields. Research at NC State and from the United Kingdom observed increasing field firmness with increasing fraise mowing depths (Baker et al., 2005). Therefore, fraise mowing can increase field firmness, providing faster fields with less thatch.

Fig. 4 Multiple dump trailers are necessary to efficiently manage fraise mowing debris.

Ancillary benefits of fraise mowing include decreased weed and disease pressure. Annual bluegrass is considered one of the worst winter weeds in all turfgrass settings- especially in sports fields. Its yellowishgreen color and seedheads disrupt field quality, and its poor, shallow rooting decreases traction and increases the likelihood of athlete injury. It produces copious seeds, and it’s increasingly more difficult to control with herbicides. Fraise mowing at ≥ 0.6 inch depth is an option to physically remove annual bluegrass plants and its seed reserves from bermudagrass athletic fields (Baker et al., 2005; Carrol et al., 2021).

Bermudagrass fields are often overseeded to provide green, ground cover for late fall through early spring sports. In the Carolinas without herbicidal intervention, perennial ryegrass can linger too long into the summer and can compromise long-term bermudagrass health. Fraise mowing at 0.5- or 0.75-inch depths provides turf managers with an effective cultural practice for removing perennial ryegrass from overseeded bermudagrass. For the fastest bermudagrass recovery, field managers should fraise mow at 0.5 inch depth in early to mid-June in the NC Piedmont.

Spring dead spot is the worst disease affecting bermudagrass sports fields. The disease attacks bermudagrass roots and stems and leads to unsightly sunken depressions of dead grass that take weeks to months to recover. Spring dead spot pressure increases with bermudagrass age and thatch accumulation. In previous research, fraise mowing at 0.3 inch depth helped to decrease spring dead spot severity and provided similar suppression as two (mid-June and mid-October) fungicide applications (Miller et al., 2017; Shelton et al., 2016). However, fungicides are still necessary for complete spring dead spot control.

Finally, fraise mowing can be used to restore surface grades on sports fields. Field slopes and surface levelness can get wonky after years of use. Surface drainage is the most effective way to drain water from sports fields. Fraise mowers – especially ones that utilize transits and receivers (Turfplaner franchise) to control cutting depth – may be used to true-up grades and slopes. This is especially true for ‘lip’ – built up infield material around baseball and softball grass edges – removal. Lips impede surface drainage and can lead to standing water to form on the infield. Lips can also create erratic hops or bad bounces that compromise player safety, as well. An annual fraise mowing of these lips can improve field playability and safety without generating a lot of debris.

Fraise Mowing: The Bad and the Ugly

Fraise mowing is a highly disruptive mechanical practice that is not for the faint of heart. Field downtime, debris management, and cost are the three main concerns with fraise mowing. Like other cultural practices, fraise mowing has collateral effects on bermudagrass quality and field behavior, which can last for weeks to months.

Fraise mowing removes all turfgrass shoots and produces an unsightly (often bare ground) surface for ≥3 weeks until bermudagrass recovers. Fields should be closed during this recovery period, which will negatively affect facility revenues. Ideally, downtime should be as short as possible. Bermudagrass recovery time can be decreased with optimal fraise mowing timing and depth, as wells as nitrogen fertilization following fraise mowing.

Bermudagrass does not begin aggressively growing until daytime and night-time air temperatures exceed 85°F and 65°F, respectively, for more than one week. With this in mind, bermudagrass should be fraise mowed when it’s growing optimally. Otherwise, its recovery will be delayed. For example, hybrid bermudagrass recovered two weeks faster when fraise mowed in mid-June versus mid-May (four weeks versus six weeks recovery). Caution should be exercised before fraise mowing before May 1st or after August 15th in the NC Piedmont. Fraise mowing too late (and too aggressively) in the late summer will result in unacceptable recovery before winter, bermudagrass decline or death, as well as increased winter weed pressure (Stewart et al., 2016). Therefore, give your bermudagrass fields ample time to recover and fraise mow in the late spring to mid-summer (1 June to 1 August in the NC Piedmont).

Fraise mowing depth has a profound effect on bermudagrass recovery. Bermudagrass recovers from growing points (nodes) on unmown rhizomes and stolons. As fraise mowing cutting depths increase, more nodes are removed, and recovery is slower. Shallow cutting depths (0.25 inches) can recover in as few as three weeks; however, one-inch depths may require ≥ 6 weeks to recover after fraise mowing. Field managers must balance thatch control and longevity of control with recovery time when selecting a fraise mowing depth.

Bermudagrass should be fertilized with nitrogen to speed up its recovery from fraise mowing. In research at NC State, hybrid bermudagrass recovered the fastest when it received nitrogen (ammonium sulfate; 21-0-0) at ≥ 0.5 lb per 1,000 square feet for three consecutive weeks after fraise mowing at 0.25 inch depth. For the more patient, weekly applications of ammonium sulfate at 0.25 lb N per 1,000 square feet or a single application of polymer coated urea at 2.0 lbs N 1,000 square feet (applied one week after fraise mowing) recovered in four weeks after fraise mowing. Normal fertility programs should be resumed after recovery to avoid excessive shoot growth and scalping.

Research at NC State did not observe a consistent increase in soil drainage following fraise mowing. Surprisingly, drainage temporarily decreased following fraise mowing at 0.5 and 1.0 inch depths by 34 and 48%, respectively, despite these depths removing >30% of thatch. Therefore, hollow-tine aerification is recommended immediately after fraise mowing. Aerification will relieve compaction and increase field drainage without negatively affecting bermudagrass regrowth from fraise mowing.

Fraise mowing produces a heck of a lot of debris! Fraise mowing one acre to 0.5 inch depth would produce 67 to 125 cubic yards of material (~35 tons). For perspective, 125 cubic yards is equivalent to ~7 mid-size sedans. This debris is made up of soil and plant material (including viable sprigs), which can be planted, discarded, or composted. Dealing with this debris can be a logistical headache – especially if a facility lacks an adequate on-site dump area. Field managers need equipment to “catch” and someplace to dump (temporarily and permanently) this debris. Equipment- ideally ≥2 tractor drawn dump trailers- is needed to efficiently catch, transport, and dump fraise mowing debris. A temporary, convenient dump site (i.e. a parking lot) is ideal to discard debris, minimize transport distances, and keep the fraise mowing ball rolling. However, the final destination for debris depends on the facility’s dump size and re-establishment needs. If neither exists, debris must be transported off-site, which may add hundreds to thousands of dollars to the fraise mowing expense.

Fraise mowers, dump trailers, and tractors to run them are not cheap. Neither are dumpsters or hauling fees to remove debris. The total cost of fraise mowing can be staggering and intimidating. Joint ownership, borrowing, or bartering with another facility – including golf courses or sod farms – may be ways to soften the financial hit of owning a fraise mower and support equipment. Hiring a contractor is an option as well. Contractor costs can vary wildly depending on fraise mowing depth and handling of debris. Typical ranges are between $0.1 to 0.2 per square foot.

Fraise mowing enables sports field managers to (potentially) remove all thatch from their fields. What would have taken years to do with vertical mowing, hollow-tine aerification, and topdressing can now be done in an afternoon with a fraise mower. Fraise mowing is an extra non-chemical tool for sports field managers to control and suppress weeds and spring dead spot, respectively. Although disruptive, visually jarring, and costly, the good of fraise mowing far outweighs the bad and the ugly.

References

Baker, S. W., Owen, A. G., & Woollacott, A. R. (2005). Physical and chemical control of Poa annua on professional football pitches. Journal of Turfgrass and Sports Surface Science, 81: 47-61.

Beard, J. B. (1973). Turfgrass science and culture. Prentice Hall, Englewood Cliffs, NJ.

Carroll, D. E., Brosnan, J. T., Unruh, J. B., Stephens, C. A., McKeithen, C., & Boeri, P. A. (2021). Non-Chemical control of annual bluegrass (Poa annua) in bermudagrass (Cynodon spp.) via fraise mowing: Efficacy and barriers to adoption. Sustainability, 13:8124.

McCarty, L. B., & Miller, G. L. (2002). Managing bermudagrass turf. Ann Arbor Press.

Miller, G. L. (2008). An evaluation of crumb rubber and calcined clay for topdressing sports fields. Acta Horticulturae, 783: 381-390.

Miller, G. L., Earlywine, D. T., & Fresenburg, B. S. (2017). Effect of fraze mowing on spring dead spot caused by Ophiosphaerella herpotricha of bermudagrass. International Turfgrass Society Research Journal, 13: 225-228. https://doi.org/10.2134/itsrj2016.10.0839

Stewart, B. R., Philley, H. W., Baldwin, C. M., & McCurdy, J. D. (2016). When will it be ready for play? Fraze mowing recovery time in bermudagrass. In: Abstracts ASA, CSSA, and SSA International Annual Meeting, Phoenix, AZ. https://scisoc.confex.com/crops/2016am/ webprogram/Paper101905.html

Shelton, C., Booth, J., & McCall, D. (2016). Impact of fraze mowing on spring dead spot severity and recovery. VA Turfgrass Journal, 12-13.