FiElD SCIENCE

Overseedingberll1udagrass:

chemical vs. natural transitionBy Scott McElroy, Ph.D.

II~verseeding bermudagrass with perennial rvegrass is agood idea for many reasons. It provides a year-roundgreen turf surface, increases winter playability, andI potentially provides greater attraction of fall. winter,and early spring play.

One of the major problems with bermudagrass overseeded peren-nial ryegrass is the spring transition. During spring transition from aperennial rvegress dominated stand to a oermuoegrass turf stand, itis very difficult to have a seamless transition where one maintainsuniform green turf. This is difficult because, in most situations peren-nial rvegrass can prevent 100% green-up by the bermudagrass. So, innon-overseeded areas when bermuoagress achieves complete green-up, the bermudagrass underlying an overseeded stand, is still par-tially dormant. An application of the a herbicide to kill the perennialryegrass can leave empty brown patches until the turf greens up com-pletely. This mottled green/brown turf would make one think that sim-ply letting the rvegrass die-out on its own would be a better option.

If one chooses to simply let the perennial ryegrass "burn-out." ortransition naturally, several new problems arise, one that is potential-ly worse than the mottled turf-clumpy volunteer ryegrass. You see,

Clumpy volunteer perennial ryegrass that has survived the previoussummer and now creates an uneven turf surface.

8 February 2006

some of the perennial ryegrass never burns out, even in the hottestof summers, This is problematic because the perennial ryegrass thatdoes not burn out often turns into volunteer "clumpy" rvegrass.Clumps of perennial ryegrass are extremely difficult to control. Manyherbicides and herbicide rates that are used to control rvegrass in adense over seeded stand are not as effective controlling volunteer rye-grass. While low and mid rates of foramsulfuron (Revolver) and trl-floxysulfuron (Monument) can control rvegrass in an overseededstand, high rates of either herbicide is needed for 100% control ofclumpy volunteer rvegress. As a side not, in every area I have been inTennessee where someone says that they completely transition theirperennial ryegrass with no herbicide, we have found clumpy ryegrass.

When's it goin' go?A second problem with letting the perennial ryegrass to burn out nat-urally is that you never know when it is going to go. If we have a dryspring the perennial rvegrass could die by mid-May, however with awet, mild summer, most of the perennial ryegrass could stick aroundall summer. thus making the volunteer rvegrass situation worse. Witha natural transition you have no control.

Rapid death of the ryegrass left open bare ground areas due tosuppression 01 the bermudagrass.

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Table 1: Pros and cons of natural versus chemical transition of overseeded tyegraee to bermudagrass turf.

ProsCost- Free

Cons

emova is so euRemoval is sometimes too slow, if not at all

f ,

Greater propensitiy for clumpy ryegrass invasion due to partialstand survival aka Clumpy Ryegrass

Greater survival of perennial rvegrass in the summer can decreasebermuda grass health

Chemical TransitionPros Cons

Potential for slow ",ml transrnc Cost- Definitely 110tfreeYou control when you want the perennial ryegrass removed. Seamless transition does not a1w8>O:soccur.Proper timing of ryegrass removal insures an adequate Repeat applcations for a seamless transition is going to bebermudagrass growing season more laborious.

Lower use rates and repeat applications of sulfonylurea herbl-coes can improve the potential for a seamless transition.

A third and final problem of letting the perennial ryegrass transi-tion naturally is that allowing perennial rvegrass continue to surviveearly into the summer is detrimental to the overall termudegrassstand. Due to the potential for winter-kill or cool springs that delaybermuoagrass green up in some areas, bermudagrass needs all thegrowing time it can get during the late-spring and summer. Expertsagree, allowing 90 to 120 days of good growing conditions forbermuoagrass during the summer is a good rule to follow when tryingto optimize bermuoagress health. This means that bermudagrassneeds June, July, August, and part September of growing for optimizedstand health. Allowing perennial ryegrass to contaminate thebermuoagress stand will decrease stand health by decreasing thenumber of uninhibited days of prime growing conditions.

Chemical pros and consLet's start with the cons (see Table 1). The main negative is that it isdifficult, even when herbicides are used, to remove the perennial rye-grass while maintaining 100% green turf cover throughout the transi-tion. Maintaining 100% green-turf cover would insure a completeseamless transition, as the perennial rvegrass slowly dies, thebermudagress just takes over.

The herbicide that provides the slowest kill, pronamide (Kerb)often does not achieve 100% control and a seamless transition is notalways achieved. A cool period with high cloud cover during the timewhen the perennial ryegrass is dying can leave the bermudagrassstagnating, struggling to enter a period of vigorous growth. A weatherpattern such as this can prevent that seamless period from occurring,leaving mottled green and brown turr.

What about the pros? The biggest pro to me is control. You havecontrol over when you want the ryegrass removed. Newer herbicidesin the sulfonylurea family, such as trifloxysulfuron (Monument) and

10 February 2006

foramsulfuron (Revolver) for example. can provide a relatively quick,100% elimination of the perennial ryegrass (Table 2). But then again,if the weather conditions are not optimal, the tenrnoegrass can stillstagnate under cool conditions.

What should I do?The first thing you should do is remember what your primary concernshould be for that turf: bermudagrass health. In an athletic field orgolf course situation, if you lose your bermudagrass base you aregoing to get a decrease in wear tolerance during the overseeded timeduring the fall, winter, and spring. If you ailow the perennial ryegrass

to linger longer than it should. you are creating a situation that ispotentially decreasing bermuoagrass heaith. A decrease in overallhealth of the bermudagrass can increase the propensity for second-

ary problems such as winterkill, or potentially reduced wear tolerance.Second, remember that perennial ryegrass is primarily for appear-

ance. You are creating a more resilient surface for the fall and earlyspring footbail and baseball season or simply trying to improve the

continued 011 page 22

Table 2. Primary products utilized for overseededperennial ryegrass in berrnudegress turf.

pronamide 1.5·3.0 Ib/a 3-6 weeksKerb

Monument trifloxysulfuron 0.3 - 0.56 ozja 2-3 weeks

Revolver foramsulfuron 17.4 fI oz/a 2-3 weeks

rimsulfuron 0.5·1.0 ozja 2-3 weeksTranXit

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FIELD SCIENCE

Update on infieldskin playability

By Karl Guillard, Seth A. Goodall, William M. Dest, and Kenneth R. Demars

Iaintenance budgets for baseball and softball fields areoverwhelmingly focused on the infield, due to the labo-rious nature of maintaining the skinned area. Thedemand for high quality infields is attributed to the factthat as much as 75% of the game can be played on

this portion of the field (Zwaska. 1999). Therefore, the goal of mostgroundskeepers is to maintain their infield skins in peak playing condi-tions, This is accomplished in a variety of ways including grooming,watering, and the application of amendments or soil conditioners.

The intensity and frequency of these practices, however, are depend-ent upon the top mix materials that make up the infield soil. Commonly,the composition of the skinned infield soil varies greatly from one fieldto another even though guidelines for construction and maintenancehave been developed for these purposes (70 to 85% sand and 15 to

140 cc rate, tonsjM

.0 .0.5 .1 .212010080604020

0Silt Loam Coarse Loamy

Loam Sandy SandLoam

Figure 2: Hardness. Gmax

35% silt and clay; ASTM, 2005). Recommendations from experi-enced field managers call for a soil with 50 to 75% sand, 15 to 35%silt, and 15 to 35% clay (Zwaska, 2002), but this advice may not befollowed regularly.

Because of the differences in the materials used for construction,soils of varying textural class, particle size distribution. and shapes areinstalled into skinned infields and tccoressec with amendmentsdepending upon cost, level of play, geography, availability, demand forcertain visual attributes, and ability of a sales representative to marketa product. These variations in the composition of the surface materialsinfluence soil physical properties, which in turn may affect the playabil-ity of the skinned infield surface, including hardness, traction, friction,and the movement of balls entering onto and leaving the skin surface.

The lack of research and understanding of these attributes forcesthe field manager to rely more on trial and error oradvice from experienced peers about practices thatproduce desirable results. instead of recommenda-tions based on scientific measurements and analy-ses. There is little scientific information on how cal-cined clays affect physical properties of skinnedinfields and subsequent ball reaction to the surface.The lack of information on ball response and physi-cal property changes of skinned infields whenamended with calcined clay provided the motivationfor our research. A full report of the results can befound in Goodall et al. (2005).

Skinned infield plots were constructed at theUniversity of Connecticut's Plant Science Researchand Teaching Facility in Storrs, Connecticut. The plotsconsisted of five different soils of varying texturalclass and sand fraction distribution amended withfour rates (0, 0.5, 1, and 2 tons/a.oou sq. ft.) of cal-cined clay (Turface Pro League from Profile Products).The added calcined clay represented half, full, andtwice the recommended rate by the manufacturer fornewly constructed infields with high sand content.

The soils were obtained from five Northeast soildistributors, and are used widely in baseball and

12 February 2006

LoamyCoarseSand

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FiElD SCIENCE

softball infields in our region on both low- and high-end fields. The soilclassified as a loamy coarse sand in Table 1 is actually a crushed rockproduct manufactured primarily for skinned infields. Even though a clayfraction was determined for this material based on particle size analy-sis, it does not possess clay mineralogy properties (i.e .. cohesivecharacteristics).

Once the infield plots were established, packed, and groomed tosimulate a skinned infield on game day, we took the following meas-urements on each soil-calcined clay rate combination: surface hard-ness with a Clegg Soil Impact Tester; surface traction using a fric-tion/traction apparatus modified with steel baseball cleats: static ball-to-surface friction using a disc apparatus with two plates that held fourbaseballs; and dynamic ball-to-surface friction using a pendulum appa-ratus. Samples of the soils with and without the calcined clay were ana-lyzed in the laboratory for bulk density, saturated hydraulic conductivity,and shear strength.

Bulk density decreased and saturated hydraulic conductivity (per-meability) increased across all soils as the rate of calcined clayincreased. In situations where skinned infields would benefit from adecrease in bulk density and an increase in permeability (e.g., com-pacted conditions), the incorporation of calcined clay would achievethis goal. Improvements to infield materials that have a low permeabil-ity by incorporating calcined clay or by selecting materials with a high

120

100

80

60

40

20

0Silt

Loam

cc rate,tonsjM

LoamyCoarseSand

CoarseSandyLoam

LoamySand

Loam

Figure 1: Dry Shear Strength, Ibs in"

permeability are important in regions where wet weather prevails orwhere the infield cannot be covered before rainfall (which is often thecase with municipal fields). On the other hand, materials with low per-meability having a high moisture holding capacity could be advanta-geous in drier climates.

Dry Y5. wet & strengthShear strength of a soil gives an indication of the binding capacity ofthat soil. Soils with greater cohesiveness will require more force toreach shearing; when the binding between soil particles is broken.From a practical standpoint, shear strength is important with skinnedinfields since it is positively correlated to traction and friction. Playersrequire adequate traction for movement between the bases (running,and stability for fielding and making throws); frictional resistance influ-ences sliding properties and ball reaction to the surface.

If a soil relatively high in silt and clay content (as shown in our study)is wetted. packed. then allowed to dry, shear strength is far greater in

Circle 116 on card or www.oners.ims.ea/5904·116 Student researcher Seth Goodall In the test plots at UConn.

www.greenmediaonline.com14 February 2006

the dry condition than in the wetted state. This canhappen with infield skins resulting in a soil that isharder to break up and groom once it dries followingwetting. Calcined clays are commonly applied to theskins when this occurs. Our results showed that thesoils in the study, except for the loamy coarse sand,generally decreased in shear strength when compar-ing the lower versus highest rates (see Figure i). Asexpected. coarser-textured soils exhibited less shearstrength than the finer-textured soils. Overall, the siltloam, at dry and moist conditions, exhibited thegreatest strength and least amount of weakeningwith the addition of calcined clay, which is attributedto the silt loam's greater particle cohesiveness.Accordingly, coarse-sandy soils may exhibit greatershear strengths when their clay fraction is signifi-cantly greater in proportion to the silt fraction.Because shear strength of an infield soil will affecttraction and friction, the field manager should keepthis in mind as the long-term application of calcinedclays to infield soils may reduce their shear strength over time, partic-ularly with finer-textured soils.

Surface hardness of the soils responded differently across calcinedclay rates; the addition of calcined clay significantly increased more sowith the coarser-textured soils than with the finer-textured soils (Figure2). It may seem a bit counter-intuitive that hardness would increasewith the addition of a coarse particle sized amendment, but we thinkthis may be a result of the interlocking of the sand-size calcined clayparticles when packed. Traction was positively related to shearstrength, but we could not find any direct rate effects of the calcinedclay additions on traction. Grooming and loosening the infield surfacesbefore making traction readings with the disc apparatus may havemasked any direct calcined clay effects.

Dynamic ball-to-surface friction increased as soils became finer intexture and decreased with increasing calcined clay rates (Figure 3),However, the sandier soils were less affected by the calcined clay addi-tions than the finer-textured soils. The higher frictional resistance of

FiElD SCIENCE

0.80.70.60.5

0.4

0.30.20.1

o

cc rate, tonsjM

SiltLoam

Loam CoarseSandyLoam

LoamySand

LoamyCoarseSand

Figure 3: Dynamic Friction, indexthe silt loam and loam soils can be attributed to their greater shearstrength compared with the other soils in our study. Static oau-to-sur-face friction results duplicated the same patterns as the dynamic ball-to-surface friction, and so were not shown.

Dynamic ball-to-surface friction has application for skinned infieldsin situations where ball rebound velocity off the surface is perceivedto be a function of an unacceptably hard surface, when, in fact, it maybe due to a low frictional coefficient of that surface. We have used thependulum device to distinguish differences on baseball skinnedinfields where hardness values were actually lower for surfaces with ahigher ball rebound velocity off the surface compared with skinnedinfields that had a lower ball rebound velocity. This suggested that sur-face hardness per se, was not resulting in the higher ball velocity offthe surface,

The pendulum device, however, was able to show that the dynamicbatl-to.surtace friction was significantly lower on the skinned infieldwith the higher ball rebound velocity. Therefore. the reduced frictionresulted in less slowing of the ball velocity as it rebounded off the

Devices used for measuring traction, static ball-to-surface friction, and dynamic ball-to-surface friction of skinned infield plots at the University of Connecticut.

16 February2006 www.greenmediaonline.com

FIELD SCIENCE

surface. This suggests that the frictional properties of certain surfacesshould be taken into account along with hardness when determiningreasons for unacceptably fast rebound off the surface

The decision to add calcined clay to fine-textured soils should bemade with consideration of the potential changes in surface friction. Ifthe objective were to slow the velocity of the ball off the surface, thencalcined clay application rates should be limited on fine-textured soils.Addition of calcined clay would only serve to reduce surface friction andmay not achieve the goal. On the other hand, if ball velocity off the sur-face of fine-textured soils is deemed unacceptably slow, then additionsof calcined clay may help to reduce the surface friction. leading to fasterball rebound from the surface.

The results of this study suggest that the playability of skinnedinfields can be affected by soil composition and the calcined clayrate. In general, the fine-textured soils responded differently thanthe coarse-textured soils for most measurements. The effects ofcalcined clay are probably attributable to the potential modificationof the textural class of a finer-textured infield skinned soil to oneof a coarser-textural class. Therefore, addition of calcined clay tofine-textured soils may cause them to react similarly to coarser-tex-tured soils.

Although our study was not long-term. the results suggest thatrepeated surface incorporation of a calcined clay into a skinned infieldwith a finer-textured soil could lead to changes in playability by chang-ing the physical properties. On the other hand. coarser-textured infieldsoils would be more resilient to changes in physical properties underrepeated calcined clay additions because of more similar particle sizesbetween the soil and the amendment.

We know from experience and from player and coach comments thatdifferent infields play differently. Determining those differences andrelating them to playability will be an important advancement in suc-cessful skinned infield management. Objective measurements similarto the ones used in our study will allow for a more scientific approachto skinned infield management and less reliance on trial and error. Thisraises the possibility that playing surface standards might be developedfor skinned infields using the techniques employed in Our study.

The next step in this line of research is to ascertain the relationshipbetween objective measurements and playability. Our preliminaryresults do not allow us to make specific recommendations at this pointbecause we are not sure what the numbers mean with respect to actu-al playability of the infield. More research is needed before reachingthat endpoint. This would include quantifying infield skins for their hard-

ness. traction. frictional coefficients, shearstrength. etc .. then matching those values toplayer preferences and acceptability.Moreover, developing meaningful values fromobjective scientific measurements will takethe guesswork out of how much of a particu-lar amendment should be applied to a specif-ic soil to reach a desired goal for playability .•

Circle 162 on reply card or www.oners.1ms.ca/5904-162

18 February 2006

ReferencesAmerican Society for Testing and Materials.2005. Standard guide for construction andmaintenance of skinned areas on sportsfields. F2107-Q1e1. ASTM International. WestConshohocken, Pennsylvania, USA.

Goodall, SA, K. Guillard, WM. Dest. andK.R. Demars. 2005. Ball Response and trac-tion of skinned infields amended with calcinedclay at varying soil moisture contents. Inti.Turfgrass Soc. Res. J. 10:1085-1093.

Zwaska, P. 1999. Infield soils and top-dressings. sportsTURF 15(3}115:121.

Zwaska, P. 2002. Infields for truest play.Landscape Manage, 41(5):6Q.-65.

Dr. Karl Guillard is a professor of agronomyat the University of Connecticut He can bereached at karl.guiflard@uconn.edu. Seth A.Goodall, William M. Dest, and Kenneth R.Demars are his students who assisted inthis research.

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22 February 2006

aesthetic appearance of dormant bermuda-grass. The additional wear tolerance that aperennial ryegrass overseeding provides isminimal at best and can often decrease thehealth of the bermudagrass during springgreen-up, Let's face facts, the primary reasonfor overseeding is aesthetics, period,

So here is what you do. First, plan yourspring transition somewhere between May 1

and June 15 (more southern areas such asFlorida and Texas can go earlier). Any earlierthan May 1 and the bermudegress can stag-nate and not fill in fast enough. Any later thanJune 15 and you are encroaching too far intothe optimum bermudagrass-growing season.

Next, determine why you need the over-seeding in the spring. Do you have a latespringjearly summer tournament, springbaseball/softball season, or spring trainingfor football? After your main event is com-pleted, chemically remove your overseededgrass and get the bermudagrass going. Andas much as I hate to say it, you have toteach management about the problems oftransition. It is just part of overseeorng andthe fields may not look their best for a cou-ple of weeks.

Third, face facts: If you've got the moneyto buy the seed, you've got the money tochemically remove it. So take control of thesituation, remove the ryegrass on your time

schedule, and optimize the growing potentialof your bermudagrass.

Figure 3 provides a flow chart of somebasic questions you can answer to deter-mine what is the best method, natural orchemical transition, is the best for you.Because in the end, you have to do what isbest for your facility taking into account, envi-ronmental, usability, aesthetic, time, andbudgetary constraints.

It is my opinion that some of us shouldtake a step back and consider why we areoverseedlng in the first place. If you arethinking that you don't have the budget tochemically remove the ryegrass, then youdon't have the budget to overseen. plain andsimple. For most, chemical removal is part ofoverseeding. It is not an option.

Finally, some of us need to remember thatwe are in the business of growing bermuda-grass. If you lose your berrnudagrass baseyou will have nothing to hold you over seed-ing. And a young seedling stand of ryegrassunprotected by the stolons of berrnuoegressdoes not last long at all In all cases, dowhatever is necessary to maximize thegrowth of the bermudagrass .•

J. Scott McElroy, Ph.D., is a Turtgrass WeedScientist at the University of Tennessee inKnoxville. See http://turfweeds.utk.edu.

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