An early history of thatch management
Mat first appeared in the literature on golf course management more than 100 years ago. Recent research and improvements in turfgrass equipment have made controlling thatch-mat an easier task.
William L. Berndt, Ph.D.
Thatch-mat from a FloraDwarf ultradwarf hybrid bermudagrass putting green in Fort Myers, Fla. This sample was photographed in the year 2000. Photos by W. Berndt
The terms thatch and mat have existed in the turfgrass literature for over a century. In his 1916 article “Speeding golf turf production,” Reginald Beale wrote about producing close-matted golf turf (4). He said that “first-class golfing turf should be so thick and fibrous that it is impossible for the ball to fall through the turf and come to rest on hard ground.” He stated that close-matted turf could be produced on greens within a year by sowing the seeds of “dwarf matting grasses” at rates of 600 pounds/acre. In the 1917 book Turf for Golf Courses, Charles B. MacDonald from Shinnecock Hills argued that creeping grasses, such as creeping bentgrass (Agrostis stolonifera L.), Rhode Island bentgrass (A. capillaris L.) and fine-leafed fescues (Festuca species), required at least three years to form suitable mat on putting greens when seeded at rates of 3 pints/9 square yards (24).
Mat: For good or for ill?
While the formation of mat was desirable, negative references about it began to emerge. In 1925, excessive matting was occurring on Ekwanok creeping bentgrass greens in Hot Springs, Va. (19). Excessive mat on these greens was said to prevent close mowing and interfere with the application of topdressing. Matting on these greens was addressed experimentally by sharpening the teeth of a steel rake to knife edges, then dragging the sharpened rake across a portion of one of the greens in two directions. After raking, the grass runners were said to be standing upright at a height of 2 to 3 inches (5 to 7.6 cm). This experimental plot was mowed as closely as possible, fertilized with ammonium sulfate, and then topdressed with two-thirds loam and one-third sharp sand. After two to three weeks, the treated turf was said to have returned to a normal appearance. The author said, upon reflection, that had the grass been cut short enough in the beginning, and had heavy topdressing been done routinely from the start, raking may not have been needed. An initial recommendation resulting from this experience, with the intent of keeping the grass growing upright and preventing severe matting, was to cut the grass short during the early establishment period, then topdress it as heavily as the green would stand, and then apply double the quantity of topdressing. Modern-day thatch management was born.
Topdressing (left), vertical mowing (center) and aerifying (right) are the primary cultural practices performed for managing thatch-mat. Topdressing essentially dilutes thatch-mat; vertical mowing and aerifying mechanically remove thatch-mat.
In the early 1930s, the USGA Green Section began making recommendations for controlling excessive matting on creeping bentgrass greens (13,14). It advised cutting back on fertilizer, and occasionally raking greens thoroughly with a sharp-toothed garden rake. Pulling up of runners should be followed by close mowing and topdressing. Raking was expected to result in an unattractive appearance, as greens were essentially being scalped, but it was said that this should not detract from putting quality. There was a divergence of opinion on topdressing, as frequent, light topdressing was referenced in 1930, while heavy topdressing was referenced in 1931.
Also in 1931, a machine called the Efficiency Lawn Renovator was introduced for renovating bermudagrass (Cynodon species) and similar types of turf (1). This gas-powered machine, with dual power-driven reels that revolved toward each other in counterrevolutions, had the effect of steel fingers grasping and tearing apart the mat of grass. This appeared to be a forerunner of the Mataway.
Controlling thatch and mat
In the early 1940s, the term thatch began appearing in the literature. Thatch was linked to development of localized dry spot (22), and the term may have evolved because water-repellent thatched roofs were popular for golf course structures (2). It was also recognized in the 1940s that formation of excessive mat, or thatch, was becoming increasingly serious for both creeping bentgrass and bermudagrass greens (15,16). Wartime modifications in greens maintenance practices, such as higher mowing heights and less frequent topdressing, led to increased mat formation. A dense mat of leaves and stolons was linked to development of grain and increased susceptibility to summer diseases and snow mold. It was said that in severe cases, the mat of dead and dying stolons and roots might become so thick that it would cause the growing layer of grass to lose contact with soil, preventing the uptake of adequate moisture.
Figure 1. Influence of the rate of natural organic nitrogen (N) on thickness of Kentucky bluegrass thatch in 1989. Natural organic nitrogen was applied at rates of 0, 2, 4 and 8 pounds of actual nitrogen/1,000 square feet (0, 9.76, 19.5 and 39 grams/square meter) using three different natural organic fertilizer materials. Four applications were made in 1989. As the rate of natural organic nitrogen increased, thatch thickness decreased.
In 1944, the Green Section recommended scarification to control excess mat. Vigorous raking and cutting — first in one direction, and then in a second direction at a right angle to the first — was followed by generous topdressing with sandy loam containing some nitrogen (16). The Green Section advised working the topdressing into turf using a brush or mat, or by spiking. The Green Section said that if scarification could be done while growing conditions are favorable — before or after hot weather — putting green recovery would be prompt, putting quality would be improved, and severe attacks of summer diseases would be materially reduced.
Within a decade, the term thatch began to appear more frequently (3,10,21,23) and was used synonymously with mat (8). At that time, it was recognized that aerifying could help overcome thatch conditions that inhibit infiltration of water into the root zone (3,21,23). The consensus of the Philadelphia Association of Golf Course Superintendents in 1951 was that aerifying should be done whenever needed throughout the playing season on every type of turf (3).
In 1953, mat was said to be the bane of the superintendent’s existence, though it was still thought to be an important component of putting quality (28). The USGA Green Section defined mat as an undecomposed mass of roots and stems hidden underneath green vegetation, usually between it and the soil surface (28). Factors in accumulation were said to be infrequent, high mowing coupled with light traffic, turfgrass type, and constraints on the maintenance budget (8,28). Another factor was slow decomposition of dead stems, stolons, leaves and roots; grass was said to produce organic matter faster than it could decompose (8).
Effect of natural organic nitrogen (N) on thatch thickness in Kentucky bluegrass in 1989. Thatch from untreated field plots (left) was nearly twice as thick as thatch treated with natural organic nitrogen at 8 pounds/1,000 square feet (39 grams/square meter) (right) (see Figure 1).
Control of mat in the early 1950s was accomplished biologically and mechanically, with both methods used on the finest golf courses (8,28). Bacteria were said to be the key to biological decomposition, and raking, combing, aerating and close, frequent mowing were the keys to mechanical removal. The proliferation of bacteria was said to be stimulated by aeration, adequate levels of soil moisture, a near-neutral pH facilitated by applying lime as needed, and the availability of sufficient nitrogen. Mowing greens six to seven times per week at 3/16 inch (4.76 mm) to ¼ inch (6.35 mm) was said to discourage mat formation. It was also said that after mat had accumulated, the turf should be raked in several directions during both spring and fall, and then topdressed. Raking was always to be done before topdressing was applied. Burying a mat of grass with topdressing, without it contacting the underlying soil, was considered an “unforgivable sin,” as doing so created a layer of organic matter that interfered with root penetration into the soil (28). In 1956, the USGA Green Section wrote that wetting agents could help improve the wetting of thatched areas, which are like peat because they are difficult to wet (18). This is important, because water repellency favors slow decomposition.
Until the 1960s, the term thatch had been used interchangeably with mat, and was considered an accumulation of stems and leaves built up on the surface of putting greens (17). But, in 1964, the terms were said to relate to different conditions (9). Mat was said to be an undecomposed mass of living roots and stems hidden underneath green vegetation, whereas thatch was described as an accumulation of dead but undecomposed stems and leaves at the soil surface (9). The occurrence of both conditions together was reported to be possible, but it was also said that either could occur singly.
A more precise definition for thatch emerged in 1966: a tightly intermingled layer of living and dead stems, leaves and stolons that develops between the green vegetation and the soil surface (26). However, the perception that mat was a network of living vegetation, and thatch was dead, residing under live turf, persisted well into the 1970s (20,25).
Figure 2. Influence of rate of urea nitrogen on thickness and bulk density of Kentucky bluegrass thatch in 1989. Urea nitrogen was applied at rates of 0, 2, 4 and 8 pounds actual nitrogen/1,000 square feet (0, 9.76, 19.5 and 39 grams/square meter). Four applications were made in 1989. As the rate of urea nitrogen increased, thatch thickness decreased and bulk density increased. Thatch became thinner and less fibrous as the rate of urea nitrogen increased.
The results of a nine-year study on Tifgreen 328 hybrid bermudagrass (Cynodon dactylon L. (Pers.) var. dactylon × C. transvaalensis Burtt-Davy) greens was published in in the USGA Green Section Record in 1969. It showed that topdressing with soil several times per year was effective in reducing the accumulation of thatch (27). Vertical mowing alone was not considered effective for controlling thatch on bermudagrass greens, but did improve putting quality by eliminating acute grain. The data showed that a combination of vertical mowing and soil topdressing provided the greatest control of thatch and a truer putting surface than either treatment alone. It’s interesting that in 2017, nearly 50 years later, topdressing has been said to be the most important component in managing organic matter in golf course greens (11). Topdressing has been used for managing thatch since the early 1900s, and probably earlier.
Thatch and mat management today
In today’s turf management world, there are no hard and fast rules for managing thatch or mat, more recently called thatch-mat (5), and definitions are still evolving (12). Everyone manages thatch-mat a bit differently because of differences in the thatching tendencies of modern cultivars, differences in management styles and personalities, and budgetary constraints. For the most part, integrating a number of strategies may be the best path to the successful management of thatch-mat. Such strategies include but are not limited to:
- Topdressing with suitable material at suitable rates at appropriate intervals. Generally, sand is used for topdressing on most putting greens, although not exclusively. Sand topdressing has its own issues (that is, particle size, hydrophobicity, angularity, etc.). Ideally, topdressing material should match the base greens mix. Using material substantially finer than the underlying mix can result in layering problems (a perched water table at the surface of the green). Using a light, frequent approach to topdressing, avoiding the formation of layers in the profile, may be the best way to go. Laboratory tests can help determine whether a topdressing material is suitable for greens.
- Vertical mowing or turf grooming coupled with brushing. Surface cultivation should always be done at appropriate depths and blade spacings, and at appropriate intervals. Verticutters are the modern-day equivalent of a sharpened steel rake.
- Aerifying with conventional aerifiers or sand/water/air injectors. As with surface cultivation, subsurface cultivation should always be done at appropriate depths and at appropriate intervals and spacings. Never aerify for the sake of doing so. Define aerification objectives, and select the appropriate machine for the job.
- Fertilizing with appropriate levels of nitrogen and other nutrients at appropriate intervals and times. Always consider the effect of the nitrogen carrier. Ammonium sulfate is acidifying, while calcium nitrate increases pH. Generally, a light, frequent approach to nitrogen fertilization may be the best route, depending on turf type.
- Applying pesticides judiciously. Many pesticides (insecticides and fungicides) act to increase thatch-mat by interfering with the activities of macro-decomposers (insects and earthworms).
- Liming to maintain a near neutral pH in the thatch layer to encourage the proliferation of soil biology, stimulating decomposition activities. Chances are that thatch-mat may be acidic, as decay of organic matter produces H+ (that is, acidity). It may be advisable to determine the pH of the thatch-mat layer, as it may differ from that of soil underlying it.
Figure 3. Influence of nitrogen carrier and insecticide (chlordane) on accumulation of Kentucky bluegrass thatch in 1988. Nitrogen was applied at a rate of 1 pound actual nitrogen applied/1,000 square feet (4.88 grams/square meter) using either urea nitrogen or IBDU nitrogen, with or without chlordane. Check plots received no nitrogen. Applying insecticide led to significant accumulation of thatch in one growing season.
Developing a set of effective management tactics requires an understanding of how these cultural practices and the environmental conditions they create can influence the dynamics of thatch-mat. Information regarding topdressing, aerification and vertical mowing is prolific, but data on some of the other aspects of this consortium are lacking.
Fertilization with nitrogen has been said to lead to thatch accumulation. This may or may not be true. Applying nitrogen at high levels without implementing thatch management practices may indeed stimulate thatch accumulation. On the other hand, nitrogen may be limiting for thatch decomposition.
During the 1980s, natural organic nitrogen fertilizers were applied to plots of heavily thatched Kentucky bluegrass (Poa pratensis L.) at rates of 0, 2, 4 and 8 pounds nitrogen/1,000 square feet (0, 9.76, 19.5 and 39 grams/square meter) four times over the course of one growing season (6). This resulted in a linear decrease in thatch thickness (Figure 1). At the high rate of nitrogen, thatch was reduced from a mean of 0.94 inch (2.41 cm) (untreated) to an average of 0.60 inch (1.54 cm), which was a 36% reduction.
In supporting research (7), fertilizing heavily thatched Kentucky bluegrass with urea-nitrogen at 2 pounds nitrogen/1,000 square feet (9.76 grams/square meter) reduced thickness from 1.18 inch (3.0 cm) to 0.83 inch (2.1 cm) (Figure 2). At 8 pounds urea-nitrogen/1,000 square feet (39 grams/square meter), thickness was reduced to 0.59 inch (1.5 cm). As urea-nitrogen rates increased, so did the bulk density of thatch, meaning mass per unit volume increased.
Effect of insecticide (chlordane) on thatch accumulation in Kentucky bluegrass in 1988. Thatch from field plots receiving no insecticide (left) compared with thatch from plots treated with insecticide (right). Treating turf with chlordane caused an increase in thatch thickness and a reduction in bulk density, meaning thatch was more fibrous (see Figure 3).
Treating Kentucky bluegrass thatch with high levels of natural organic nitrogen or urea-nitrogen changed its physical character. This does not mean to suggest that nitrogen levels should be increased on fine putting greens, but that superintendents should understand that decay of organic matter depends on the availability of sufficient nitrogen (along with water and air). Thatch decomposers (microorganisms, insects, etc.) must acquire nitrogen to generate proteins (enzymes), which are critical to sustaining their activities.
Application of pesticides can affect accumulation of thatch. Treating Kentucky bluegrass with 1 pound nitrogen/1,000 square feet (4.88 grams/square meter) did not increase or decrease thatch thickness (7). However, concurrent treatment with insecticide (chlordane) caused a significant increase in thatch thickness in field plots (Figure 3). In a two-year study conducted in 1988-1989 (7), thatch treated with urea-nitrogen and insecticide increased in thickness from 1 inch (2.5 cm) to 1.37 inches (3.5 cm) in year one, and from 1 inch (2.5 cm) to 1.22 inches (3.1 cm) in year two. In plots treated with IBDU nitrogen and insecticide, thatch thickness increased from 1.10 inches (2.8 cm) to 1.45 inches (3.7 cm) in year one, and from 0.8 inch (2 cm) to 1.18 inches (3 cm) in year two. Treating plots with insecticide also resulted in significant decreases in the bulk density of thatch; thatch appeared more fibrous, with less mass per unit volume. In plots treated with urea-nitrogen and insecticide the bulk density decreased an average of 60%, from 1.43 to 0.58 pounds/square foot (6.98 to 2.83 kilograms thatch/square meter). This finding was significant. Insecticide retarded movement of underlying soil into thatch, which reflected decreased activities of macro-decomposers such as earthworms and insects. Treating Kentucky bluegrass thatch with insecticide changed its physical character. Retarding the activities of macro-decomposers with chlordane led to accrual of thatch, even in the control plot receiving no nitrogen. Insecticides likely influence thatch-mat dynamics on putting greens and in other highly maintained turf.
Applying thatch control products
Stimulating the biological decay of thatch with commercial products has been tried for many years, and numerous products are available for this purpose. Whether they work is subject to debate.
Some of these products contain the enzyme cellulase, a hydrolytic enzyme that dissolves cellulose, a constituent of plant cell walls. The purpose of treating thatch with cellulase is to hasten its decomposition by inducing hydrolysis (decay) of the cell walls of thatch constituents.
Figure 4. Influence of the enzyme cellulase with time on the decay of thatch-mat in 2009-2010. Cellulase from Trichoderma reesei was applied to TifEagle and TifDwarf hybrid bermudagrass thatch-mat in a laboratory study at a rate of 0, 10 or 20 mg/gram thatch-mat (that is, 1% or 2% by weight). Treating with 20 mg cellulase hastened decay of thatch-mat significantly during the first few days of the study, but at 15 days after treatment, there were no differences compared with the untreated control. Untreated thatch ultimately released as much organic carbon as the thatch-mat that had been treated with cellulase.
In laboratory research conducted in 2009-2010, pure cellulase from a fungus called Trichoderma reesei was applied to hybrid bermudagrass thatch-mat at rates of 0, 10 and 20 milligrams cellulase per gram of thatch-mat (5). This was the equivalent of treating it at 1% or 2% by weight. The thatch-mat was wetted with water, then the release of carbon dioxide from experimental units was measured as an indication of decay. The idea was that if comparatively high levels of carbon dioxide were released from thatch treated with the enzyme, then the enzyme hastened thatch decomposition (that is, the carbon in the organic matter mineralized to carbon dioxide).
Cellulase did in fact increase the rate of decay of what is termed fast-pool carbon, which is the highly soluble organic carbon fraction of thatch-mat (Figure 4). However, it was also discovered that only about 7% to 8% of hybrid bermudagrass thatch-mat was fast-pool carbon. The other 92% to 93% was considered slow-pool carbon (that is, hemicellulose and lignin), which is resistant to the effect of cellulase and decay in general. Cellulase accelerated the short-term decay of thatch-mat, but did not increase total mineralization of organic matter compared with an untreated control. Thus, the return on investment for commercial thatch decomposition products containing cellulase remains questionable.
Thatch-mat will continue to be a topic in turf literature for many years, as its nature and behavior are still not completely understood. Arguably, the most comprehensive reference on thatch-mat to date is “Characterization, development, and management of organic matter in turfgrass systems,” which was published in 2013 (12). The paper presents a change in thinking about thatch-mat and turf-oriented soil organic matter.
- Anonymous. 1931. Coast greenkeeper invents Bermuda conditioner. Golfdom: The Business Journal of Golf 5(2):113.
- Anonymous. 1948. Thatched root makes picturesque tee shelter. Golfdom: The Business Journal of Golf 22(9):62.
- Anonymous. 1951. Aerification and efficient turf maintenance. USGA Journal and Turf Management 4(5):29-30. (http://gsrpdf.lib.msu.edu/ticpdf.py?file=/1950s/1951/510929.pdf) Accessed Aug. 9, 2017.
- Beale, R. 1916. Speeding golf turf production. The Golf Course 1(3):21, 29.
- Berndt, W.L., R.E. Gaussoin and J.M. Vargas Jr. 2014. Cellulase accelerates short-term decay of thatch-mat. Agronomy Journal 106:781-788. doi:10.2134/agronj2013.0447.
- Berndt, W.L., P.E. Rieke and J.M. Vargas Jr. 1990. Kentucky bluegrass thatch characteristics following application of bio-organic materials. HortScience 25(4):412-414.
- Berndt, L., J. Vargas Jr. and M. Slater. 1990. Influence of insecticide and N on Kentucky bluegrass thatch. Pages 170-175. In: P.E. Rieke and M. Saffel, eds. MichiganTurfgrass Conference Proceedings, Lansing, Mich. Jan. 15-17, 1990. MTF, Okemos, Mich.
- Cornman, J.F. 1952. Mat formation on putting greens. The Golf Course Reporter 20(4):8-12, 14.
- Ferguson, M.H. 1964. Mat and thatch: cause effect and remedy. USGA Green Section Record 1(5):10-12. (http://gsrpdf.lib.msu.edu/ticpdf.py?file=/1960s/1964/640110.pdf) Accessed Aug. 9, 2017.
- Ferguson, M.H., and F.V. Grau. 1950. What about liquid fertilizers? USGA Journal and Turf Management 3(6):29-30. (http://gsrpdf.lib.msu.edu/ticpdf.py?file=/1950s/1950/501129.pdf) Accessed Aug. 9, 2017.
- Fisher, M. 2017. Soil evolution: par for the golf course. CSA News 62(6):4-7. doi:10.2134/csa2017.62.0616.
- Gaussoin, R.E., W.L. Berndt, C.A. Dockrell and R.A. Drijber. 2013. Characterization, development, and management of organic matter in turfgrass systems. Pages 425-456. In: J.C. Stier, B.P. Horgan and S.A. Bonos, eds. Turfgrass: biology, use, and management. Agronomy Monograph 56. American Society of Agronomy, Crop Science Society of America, Soil Science Society of America, Madison, Wis. doi:10.2134/agronmonogr56.c12.
- Green Section Staff. 1930. Controlling the tendency of creeping bent to mat. The Bulletin of the United States Golf Association Green Section 10(2):33. (http://gsrpdf.lib.msu.edu/ticpdf.py?file=/1930s/1930/300230.pdf) Accessed Aug. 9, 2017.
- Green Section Staff. 1931. Overcoming the matting of creeping bent turf. The Bulletin of the United States Golf Association Green Section 11(8):171. (http://gsrpdf.lib.msu.edu/ticpdf.py?file=/1930s/1931/3108170.pdf) Accessed Aug. 9, 2017.
- Green Section Staff. 1943. Remove mat of excess stolons by vigorous raking. Timely Turf Topics September: 1. (http://gsrpdf.lib.msu.edu/ticpdf.py?file=/1940s/1943/4309.pdf) Accessed Aug. 9, 2017.
- Green Section Staff. 1944. Scarification advisable before hot weather. Timely Turf Topics June: 1. (http://gsrpdf.lib.msu.edu/ticpdf.py?file=/1940s/1944/4406.pdf) Accessed Aug. 9, 2017.
- Green Section Staff. 1956a. Mowing and the thatch problem. USGA Journal and Turf Management 9(4):31-32. (http://gsrpdf.lib.msu.edu/ticpdf.py?file=/1950s/1956/560831.pdf) Accessed Aug. 9, 2017.
- Green Section Staff. 1956b. Questions and answers. USGA Journal and Turf Management 9(2):32. (http://gsrpdf.lib.msu.edu/ticpdf.py?file=/1950s/1956/560631.pdf) Accessed Aug. 9, 2017.
- Ingalls, F. 1928. Creeping bentgrass at Hot Springs, Virginia. The Bulletin of the United States Golf Association Green Section 8(9):184-188. (http://gsrpdf.lib.msu.edu/ticpdf.py?file=/1920s/1928/2809184B.pdf) Accessed Aug. 9, 2017.
- Madison, J.H. 1971. Practical turfgrass management. Van Nostrand Reinhold, New York.
- Mid-Atlantic Association of Golf Course Superintendents. 1951. Turf News Letter (August): 5. (http://archive.lib.msu.edu/tic/matnl/article/1951aug.pdf) Accessed Aug. 9, 2017.
- Noer, O.J. 1942. With O.J. Noer: South, East, and West: photo story of greenkeepers’ battles to provide the best possible playing surface. Golfdom: The Business Journal of Golf 16(3):41.
- Philadelphia Association of Golf Course Superintendents. 1951. They aerify for better turf in Philadelphia. USGA Journal and Turf Management 4(1):25-27. (http://gsrpdf.lib.msu.edu/ticpdf.py?file=/1950s/1951/510425.pdf) Accessed Aug. 9, 2017.
- Piper, C.V., and R.A. Oakley. 1917. Turf for golf courses. Macmillan, New York.
- Record, L. 1975. Thatch: a part of turf. USGA Green Section Record 13(1):9-13. (http://gsrpdf.lib.msu.edu/ticpdf.py?file=/1970s/1975/750109.pdf) Accessed Aug. 9, 2017.
- Thompson, W.R., and C.Y. Ward. 1966. Prevent thatch accumulation on Tifgreen bermudagrass greens. The Golf Superintendent 34(9):20-38.
- Ward, C.Y. 1969. Turf grass research. USGA Green Section Record 7(6):10-13. (http://gsrpdf.lib.msu.edu/ticpdf.py?file=/1960s/1969/691110.pdf) Accessed Aug. 9, 2017.
- Wilson, C.G. 1953. Matted greens contribute to poorer golf. USGA Journal and Turf Management 6(1):25-28. (http://gsrpdf.lib.msu.edu/ticpdf.py?file=/1950s/1953/530425.pdf) Accessed Aug. 9, 2017.
William L. Berndt is a former faculty member at Edison State College and Florida Gulf Coast University, and is currently the president of Environmental Turf Inc. in Avon Park, Fla.