Triplex ring is a classic example of mechanical damage.

BY STANLEY J. ZONTEK

MOWING HEIGHTTIMELINEA number of timelines have been published overthe years showing how mowing heights havegradually been getting lower. Suffice it to say, thetraditional mowing height for golf greens in the1950s to the early 1970s was X inch (6mm) to ))6

inch (5.5mm).Things began to change in the late 1970s with

the development of the Stimpmeter. This devicewas originally developed by Edward Stimpson, avolunteer for the Massachusetts Golf Association,to help locate holes on greens at courses hostingtheir tournaments. Measuring green speeds was asecondary consideration. Over time, the intentobviously changed, and an unintended conse-

Understanding and ManagingMechanical DalllageAre you hurting your greenswithout knowing it?

What is mechanical damage? Mostturf managers probably would say,"It's when I scalp the grass." They

are correct. Scalped turf is the easiest form ofmechanical damage to see and understand.However, there are other less obvious forms ofmechanical damage that can be just as injurious tothe turf, especially over time and in conjunctionwith other forms of stress.

Direct and indirect forms of mechanicaldamage are becoming an increasingly widespreadproblem worldwide on putting greens. For what-ever reasons, golfers are demanding lower andlower mowing heights to achieve faster greenspeeds, and they want these speeds on a regularbasis. Once these maintenance levels are achieved,it's hard to go back.

Most people are oblivious to the consequencesof closely cut greens on a daily basis. Here areseveral definitions and some historic backgroundon the problem of close mowing and the resultingsubtle form of mechanical damage many turfmanagers now face.

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quence has occurred. Stimpmeter readings forputting green speeds have become the measureof how golfers perceive what is "quality" in aputting surface. There is a mistaken belief that thefaster the green, the better it is.

We all know this oversimplifies a complex issue.What is not in dispute is the effect this attitudehas had on green speeds and on the gradual re-duction in putting green mowing heights overthe past three decades. There are huge conse-quences from today's ultra-low mowing heights.When will it end? The first step is to recognizethe problems associated with mowing greens asclosely as possible on a daily basis. The secondstep is to manage the grass to minimizemechanical damage.

The gradual reduction in mowing height tooksome years to occur, and today's mowing heightsare commonly Ys inch (3mm), with Xo inch(2.5mm) or lower on golf courses striving forchampionship conditions on a daily basis. Theagronomic consequences from today's ultra-lowmowing heights are significant, especially whencombined with continuous daily mowing,periodic groomings, topdressings, double andtriple cuttings, etc., along with other stresses,including low putting green fertility and theweather extremes many regions of our countrynow seem to be experiencing.

The elements are in place for the greens onmany of to day's golf courses to be weakened,albeit in a slow, gradual manner. This makesgreens, especially older greens with early-genera-tion grasses and Paa annua, more susceptible todisease, insect injury and weed problems.

SOME DEFINITIONSDirect Mechanical Damage. In simple terms,it is often scalped grass. This is an acute form ofturf injury. This type of damage can occur when:• The mower is not properly adjusted .• The mower is damaged or falls out ofadjustment .• The grass becomes soft and puffy due to hot,humid, and wet weather, and/or when the grass isover-fertilized.• The grass "rebounds" from growth regulatorapplications .• The mowing height is lowered and mowingfrequency is increased for special events.

Again, direct mechanical damage can easilymanifest itself as scalped grass, which is easilyrecognized. Corrective action, including raising

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mowing heights, mowing less often, and begin-ning a recovery process is usually quickly imple-mented once the damage has been seen. After all,even the average golfer can recognize scalpedgrass! It is the indirect and more subtle forms ofmechanical damage that are much harder tounderstand, diagnose, and appreciate.

Indirect Mechanical Damage. This is muchmore subtle way to weaken and injure the grass.Whereas the effects of direct mechanical damage(scalped grass) are easy to see and correct, theeffects of indirect mechanical damage are almostnever seen. This makes it much more difficult torealize that something is going wrong.

This type of injury is more common on oldergolf courses, especially compared to newer golfcourses that have modern sand-based greens andnew-generation grasses growing on them. Almostall of these new grasses were bred and developedto better tolerate the lower mowing heights com-mon today. They are dwarf grasses, having greaterplant density, finer blades, and greater tolerance tolower mowing heights. It can be unrealistic tocompare old vs. new courses, but unfortunately itis done all the time. This contributes to indirectforms of mechanical damage.

Predisposition. Predisposed turf is weakenedturf. The grass can be weakened by one of a longlist of factors by itself or working in conjunctionwith other factors. It generally is recognized thatonce the grass plant or stand of grass has beenpredisposed or weakened, it suffers from reduceddisease resistance, lower thresholds for nematodes,shallower roots, reduced turfgrass vigor, slowerrecovery / recuperation from traffic and otherinjury, reduced tolerance to heat, drought, shade,poor drainage, and poor grass growing environ-ments associated with poor air circulation.

Turf predisposed by mechanical damage canalso be more easily invaded by moss, algae, andweed grasses like Paa annua, crabgrass, and goose-grass. Weakened turf lacks color and density andlooks unhealthy. Predisposed turf, once infectedwith a disease, does not always respond well tofungicides. Thus, disease control is harder toachieve .

Predisposed turf almost never occurs at reason-able mowing heights and when a good puttinggreen maintenance and management program isin place. This problem of predisposition is becom-ing a common occurrence on turf cut at lowto ultra-low mowing heights. True, some grassesgrowing in some soils in some parts of the

country and under some careful (and expensive)maintenance practices can tolerate manypredisposition factors. However, this is trueManagement On The Edge.

SHORT-TERM OPTIONSAn important role of a golf course superintendentis to know when to be aggressive in terms ofmowing heights, green speeds, and overall puttinggreen maintenance, and, equally, when to be care-ful and conservative in managing the grass onthe course. The average golfer or course officialsometimes does not appreciate this importantfact.

Following are a number of options golfcourse superintendents and the managementteam should consider when managing directmechanical damage.

Prevention. It is important to recognize thatmechanical damage generally is a problem onlyon closely mown turf, and its effects are prevent-able. That is, to an extent, it is possible to preventthe grass plant from becoming predisposed andweakened. Do the obvious.• Establish reasonable mowing heights andmowing frequency jOr the grasses you have, notfor some other course to which you might becompared.• Exercise good water management. Do notover-water, and maintain reasonable surface andinternal drainage.• Grow healthy grass. Provide the turf withenough hours of sunlight, good air circulation,drainage, and enough balanced fertility, etc.• Manage the zone of organic matter accumu-lation. Topdress and surface aerate frequently, atleast once a month, to encourage root growth,promote water movement in the soil, relievesurface compaction, and allow the soil to breathe.• Modify the soil in greens that were not builtwell. Core aerate to remove the old soil, topdresswith sand to fill the holes, and maintain a goodtopdressing program. Deep aeration can alsobenefit old, tight, and slow-draining soils.• Apply plant protectant chemicals whennecessary to control damaging diseases, weeds,and insects. These chemical applications can alsoinclude commonly used plant growth regulatorsthat maintain healthier, denser, and slower-growmg grass.

Thus, the first step in managing mechanicaldamage is to prevent it from happening in thefirst place. Some might call this Common Sense

Turfgrass Management. It is not cutting edge,but it works.

MANAGING STRESSOnce the grass is under stress, there are manyoptions the turf manager can consider to relievestress and encourage turf recovery .• Raise Mowing Heights. Oftentimes, this isthe first thing to do. And although it also is thesimplest, easiest, and most cost-effective option, itis sometimes the most difficult for golfers toaccept.• Mow Less Often. When weather extremesoccur or when casual water exists on the surfaceof a green, raise mowing heights and defer mow-ing until the grass and soil can tolerate the traffic.Mechanical damage almost certainly will occurwhen the mowers are pushing water as theyattempt to cut the green.• Roll Greens. Rolling a green rather than mow-ing a weak or wet green may be a good compro-mise to maintain smooth greens with good speedwithout damaging the grass. Research has shownthat rolling greens up to three times per week haslittle long-term effect on the grass or soil.• Growth Regulators. Various plant growthregulators, including Primo (Trinexapac-ethyl),Trimmit, TGR (paclobutrazol), and Cutless(Flurprimidol), are commonly used tools to helpachieve healthy grass at higher mowing heightsand smooth, fast greens. Slower growing, chemi-cally dwarfed grass, in theory, may allow higher

Mowers must becarefully adjusted toavoid direct mechanicaldamage. A new, heavierwalk-behind greensmower was used.Although the settingswere the same, theresult was scalped turf.

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When expanding the putting green, extra care must be takento avoid injury caused by scalping.

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cutting heights and less-frequent mowing. Con-tact your regional USGA agronomist, universityturf grass extension specialist, or companytechnical representative for more information .• Topdressing. A dedicated program of light,frequent topdressing creates a situation where thegrass plant grows upward through this topdressingas it accumulates. This can insulate and protect theimportant growing points of the grass, its stemand crown. When the grass grows through thetopdressing, the mower clips the grass blades, notthe stems and crowns. This helps avoid scalpedturf. Topdressing also helps manage surfaceorganic matter and any puffiness, if or when itdevelops. Topdressing is a form of preventativemaintenance, but improperly scheduled summertopdressing has the potential of creating its ownform of mechanical damage. Be careful .• Balanced and Adequate Fertility. The grassplant needs a balance of nitrogen, phosphorus,and potassium in general ratios of 4-1-2, 3-1-2, oreven 4-1-4, and soil tests remain the best tool tomonitor soil fertility levels. At one time, it was atrend to maintain "hungry grass." Today, there isthe realization that this practice can be taken toofar. Putting greens need adequate fertilization.Some diseases, including anthracnose and dollarspot, are recognized as being diseases associatedwith low nitrogen use. Contact your local USGAagronomist or university turfgrass extensionspecialist for unbiased answers to your fertilityquestions .• Spoon Feeding. The application of lightamounts of fertilizer sprayed onto the grass is agood way to manage plant growth in the summerand stimulate recovery of damaged, stressed turfwhen bad weather conditions subside. Biweekly,weekly, or sometimes even twice weeklyapplications can be scheduled .• Aeration. It might seem counterintuitive,but aeration can be a good tool to managemechanical damage! Remember that grass rootsgrow in the soil in the presence of air. Tight soilswith few large pores restrict rooting. Also, waterdrains through the soil in these same large pores.Shallow-rooted surface growth is inherently moreprone to mechanical damage. Aeration in con-junction with topdressing helps alleviate thiscondition .• Proper Irrigation. Do not over-irrigate orseverely under-irrigate the grass. Although driergrass and soil are always preferred, there needs tobe a balance between too much and too little soil

water. One extreme is wet wilt from too muchwater in the soil, and the other extreme is drywilt from too little water in the soil. When grass iscut while it is under wilt stress, be it dry wilt orwet wilt, mechanical damage can result.• Defer Regular Maintenance. That is, if yoususpect the grass is being stressed due to weatherextremes, close mowing, double or triple cuttings,too much topdressing, aggressive grooming, etc.,don't add extra stress. Defer these treatments.Trust your agronomic intuition and commonsense. Be conservative. Defer maintenance in theshort term until the stress period passes and theturf is healthier and better able to handle thismaintenance.• Communicate. Direct and indirect forms ofmechanical damage on the golf course are notproblems for the golf course superintendent toendure quietly and alone. There needs to be goodcommunication within the management of thegolf course. People want to know how theircourse is doing. Post notices and keep the golfshop, course administration, and decision makersinformed. Emails, course newsletters, and. courseweb sites are all effective communication vehicles.This helps bring everyone "into the loop" soinformed decisions can be made on what is bestfor the course.

The goal of all this work is to manage yourexisting greens without major regrassingor reconstruction. In essence, you are"working with what you have."

LONG-TERM OPTIONSAn increasing number of older golf coursesrecognize the fact that the soil in the greensis not good, green sizes are too small, greencontours and slopes are too severe, and thegrass the staff is trying to grow on thegreens is a problem. It's a fact. In mostregions of the country, modern sand-basedgreens are better than older soil-basedgreens. New and better grasses have beendeveloped to tolerate closer mowing andhave better density, better rooting, finerleaf blades, and improved disease and stresstolerance .• Putting Green Regrassing. Manycourses choose to regrass existing greens.This occurs when the base soil in the greensis deemed acceptable, when the greens enjoyclassic design with subtleties in movement,when climatic stress factors are deemed less

severe, etc. The goal of regrassing is to replaceearly-generation grasses with newer varietieswithout a complete reconstruction of the greens.For guidance on regrassing vs. reconstruction,consult your regional USGA agronomists orother courses in your area that have regrassed.• Putting Green Reconstruction. Manyscenarios can lead to the conclusion that it is timeto rebuild old greens to modern specifications.Turf managers need to discuss the pros and conswith their owners, course officials, consultingarchitects, and their USGA agronomists. Newgrasses and new fresh soils are not panaceas, butthey are better in many ways.

CONCLUSIONHistorically, when greens were being cut at Xinch (6mm) or even at %2 inch (4mm) , loweringthe mowing heights a few thousandths of an inchseldom produced many ill effects to the grass.Today, this has changed. Our ultra-low mowingheights have themselves become a stress factorthat can trigger all kinds of problems that canthreaten the health and playability of greens.There is little margin for error with today's lowmowing heights and high golfer expectations.

STAN ZONTEK is directorif the USGA GreenSection's Mid-Atlantic Region.

Poorly timedverticutting can resultin direct mechanicaldamage to the puttinggreen turf.

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