Overseeding bermudagrass greens is a typical fall activity in preparing greens for the winter (Martin Downs Country Club, Palm City, Florida).

Overseeding:It Is A Challenge!by CHUCK GASTAgronomist, Florida Region, USGA Green Section

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y WAY you look at it, maintainingconsistent, top-quality turf conditions

on bermudagrass-based greens inthe South during the busy winter season canbe a difficult proposition. Furthermore, re-gardless of the many factors analyzed andthe educated decisions made, it's still agamble, since weather is the most importantand unpredictable factor and will ultimatelydetermine the level of success achieved.

Throughout the South the number ofgolfers per day on many courses increasesto as many as 250-300 during the winter

season, when "Snow Birds" flock south. Thispresents a real challenge to the golf coursesuperintendent, who must maintain consis-tently good-quality putting surfaces for theenjoyment of the golfers and the financialsuccess of the club or course.

To maintain a good level of putting qualityon bermudagrass greens during the winter,oversee ding programs typically areperformed. This doesn't mean, however, thatgood-quality winter putting conditionscannot be maintained on non-overseededbermudagrass. To the contrary, the ber-

mudagrass cultivar Tifdwarf, with propermanagement, has the ability to produceexcellent year-round putting quality in thesouthernmost coastal regions of the UnitedStates. That's another story, however. Thisarticle is dedicated to the practices and pro-grams associated with the overseeding ofbermudagrass greens.

Why Overseed?In deciding whether or not to overseed

bermudagrass greens, several factors must be

SEPTEMBER/OCTOBER 1993

*Percentages are by seed weight

Table 2Recommended Seeding Rates

Table 1Approximate Number of Seeds Per Pound

Ryegrass

Bentgrass

Poa trivia Us

Monostands

Perennial Ryegrass

Poa trivia Us

Bentgrass

Polystands*

85% Perennial Ryegrass15% Poa triviaUs

80% Poa triviaUs20% Bentgrass

taken into consideration. First and foremostis the geographical location of the courseand the anticipated length of time thebermudagrass will be dormant or inactivelygrowing. Naturally, areas further north or in-land in the Southern Region are more likelyto engage in overseeding programs. Theability to maintain good winter color andto provide resistance to excessive turf wearwill be major considerations in the decision-making process. Mter these factors areweighed and the decision is made to engagein an overseeding program, the followinginformation should be helpful in improvingthe odds for success.

Seeding Alternatives

Three cool-season turfgrass species domi-nate the selections used in overseedingsouthern golf course greens. They includeimproved perennial ryegrass cultivars, roughbluegrass (Poa triviaUs), and creeping bent-grasses. Several factors are involved indetermining which grass or combination of

2 USGA GREEN SECTION RECORD

250,000

6.1 million

2.3 million

Pounds per 1,000 Square Feet

26-32

10-12

3-5

25-30

8-10

grasses is the best for a particular course.They include:

• wear tolerance• color• texture• height of cut• spring transition• compatibility of blends• seed availabilityIn many situations the standard over-

seeding program consisting of a blend ofthree or four improved perennial rye grasscultivars is the selection of choice. Ryegrassexhibits far greater wear tolerance than Poatrivialis and bentgrass, making it a goodchoice for courses anticipating intense playconditions throughout the winter season.Turf-type ryegrass also provides a dark greencolor, but tends to produce a slow puttingsurface during the fall establishment periodwhen it is growing quickly and whenelevated mowing heights must be practicedto ensure good turf establishment.

Poa trivia Us has gained popularity overthe years as an overseeding alternative. Thisturf species provides excellent putting char-

acteristics and germinates and establishesquickly during the fall, thereby minimizingdisruption to play. Poa trivialis is less tolerantof traffic compared to other species andtherefore should be used only as a monostandoverseed turf cover on courses that antici-pate limited winter play. Ease of springtransition also can be expected with PoatriviaUs, which has poor heat tolerance andtherefore will not compete with the bermuda-grass as late spring temperatures rise.

Oversee ding with bentgrass also providesexcellent winter putting characteristics onbermudagrass-based greens. The improvedbentgrass varieties, however, possess goodheat and drought tolerance and thereforeshould be used with caution in the central andnorthern sections of the Southern Region toavoid spring transition problems.

Many superintendents have found thatutilizing ryegrass or bentgrass in combina-tion with Poa triviaUs provides better over-seeding results and therefore more and moreoverseeding programs are moving in thisdirection. Reduced seeding rates of bent-grass and ryegrass and easier transition pro-grams can be realized when Poa triviaUs isincluded in the overseeding mixture. (SeeTable 2.)

Timing Considerations

Whichever seeding option you choose,proper timing of seed application is criticalin determining the level of success achievedwith the overseeding program. Tables thatoutline approximate seeding dates are avail-able from seed suppliers, but the best indi-cator to determine the optimum time tooverseed is soil temperature. Research hasdetermined that the preferred soil tempera-ture range for winter overseeding is between72 and 78 degrees Fahrenheit at a depth of4 inches.

Unfortunatel y, timing of overseedingprograms often is dictated more by politicsand economics than by good principles andagronomic practices. Overseeding programsoften must be scheduled so as not to inter-fere with tournaments or to inconveniencemembers returning to their winteringgrounds. Open communication and properplanning are critical to ensure that the bestpossible overseeding results are achieved.

Surface Preparations

Specific turf management practices shouldbe performed well in advance to ensureoptimum results when overseeding. Fallaerification of greens should be performednot later than 30 days prior to the proposedoverseeding date. This allows sufficienttime to achieve complete recovery from thisoperation and reduces the potential for

spotted surface conditions that can occurwhen overseeded grasses concentrate andgerminate in aerification holes. Fall aerifi-cation is essential to reduce soil compaction,increase oxygen content within the upperroot zone, and assist in reducing excessthatch, thereby better preparing the greensfor overseeding.

The last application of nitrogen alsoshould be made at this time to allow thenormal slowing of bermudagrass shootgrowth as fall temperatures begin to decline.This will be helpful in reducing bermuda-grass competition with the newly germinat-ing cool-season turf. Fertilization of thebermudagrass at this time also will be help-ful to enhance the winter hardening processby promoting storage of essential carbo-hydrates for healthier bermudagrass plantsnext spring. Mid to late fall applications ofpotassium also are essential to assist in thishardening process.

Implementation of a plan to control annualbluegrass (Poa annua) should be performedwell in advance of overseeding. Good resultshave been reported with the use of fenarimol(Rubigan) as a pre-emergent herbicide tocontrol annual bluegrass in winter over-seeded turf. The three-application program,as per label recommendations, has providedgood results, especially when overseedingwith Poa trivia/is or bentgrass. Timing iscritical in the use of this product. To obtainoptimum results, the last application shouldbe made at least two weeks prior to over-seeding with ryegrass and at least fourweeks before overseeding with Poa trivia lisor bentgrass. It also is suggested that whenapplying Rubigan in a multiple applicationprogram, special care should be taken to varyspray patterns across the greens to ensureuniform applications. If the same directionof travel is used each time, problems associ-ated with potential 5-6x rates in the overlapareas may result.

Use of pronamide (Kerb) also has beenreported to be effective in reducing Poaannua problems associated with overseed-ing. Application of this material should bemade 45 to 60 days prior to overseeding.

On courses where the collars andapproaches to the greens are not scheduledfor overseeding, it is recommended that anappropriate pre-emergent herbicide beapplied to these areas approximately 7-10days prior to overseeding. This will be help-ful to maintain clean surrounds and elimi-nate undesirable germination of seed thatmay be tracked off the greens by foot trafficor machines. Immediately prior to overseed-ing, a band of charcoal can be applied aroundthe outer edge of the greens at a rate of 6-8pounds per 1,000 square feet to inactivateherbicide overspray in these areas and ensureuniformity of seed germination.

An old groomer reel on a rotary mower handle effectivelyprepares isolated thin twi areas for additional seeding.

Once the thin twi area is properly prepared, hand application of asand/seed mix helps reestablish a consistent overseeded turf

SEPTEMBER/OCTOBER 1993 3

Overseeding Procedures

In reviewing overseeding techniques, it isclear that many different methods can beutilized in completing overseeding programs.There are, however, a few common denomi-nators that have proven beneficial in estab-lishing overseeded turf.

Four to five days prior to overseeding, theheight of cut on the greens should be raisedto the range ofJSzto 'l'l6 of an inch. This highercut is helpful in creating a good seedbed andminimizing the chance of seed movement incase heavy rainfall occurs soon after seedapplication.

Light vertical mowing also should be per-formed during this time to open up the denseturf to promote good seed/soil contact foroptimum germination and seedling estab-lishment. Vertical mowing in several direc-tions prior to overseeding promotes uniformseed establishment across the surface ofthese greens. Debris from the vertical mow-ing should be removed by blowers, vacuums,or greens mowing equipment.

In preparing the surface for overseeding,some superintendents also find it helpful tospike the greens in several directions to fur-ther improve seed germination and estab-lishment. Spiking can be beneficial on greensthat have a tendency to hold excess water inthe upper root zone or on greens where thepresence of surface algae would inhibitgood seed establishment.

Uniform application of seed is a criticalstep in producing consistent winter puttingquality, and several innovative methods havebeen developed by superintendents in theirdesire to achieve the best results. Forexample, Milorganite has been used as acarrier for uniform seed application whensmall quantities of seed are sown. Also, dropspreaders equipped with spray can attach-ments on either side assist in clearly outliningwhere seed has been placed. Another inno-vation involves the use of rotary spreadersoutfitted with small chains attached to polesextending to the outer throw of the spreaderto define the seeded area.

An outstanding method of achievingaccurate seed application was developed byDavid Oliver, superintendent at the MartinDowns Country Club in Florida. His methodinvolves topdressing the green prior to seed-ing with approximately 0.3 to 0.5 cubic yardsof sand per 1,000 square feet. With the sandin place, the wheel tracks of drop spreaderscan be easily seen to ensure uniform appli-cation. In this situation, seeding at halfrates in two directions at 90° angles can beperformed accurately.

To reduce accidental distribution of seedoff the surface of the green due to wornspreaders or crew members' shoes, specialcare should be taken when parking utility

4 USGA GREEN SECTION RECORD

vehicles during seeding. Park the utilityvehicles immediately adjacent to the puttinggreen surface and instruct workers to enterand exit the vehicle only on the side adjacentto the green. Furthermore, seed spreadersshould be lifted from the vehicle directly ontothe green so that travel off the green iseliminated. Practicing these steps will reducethe undesirable introduction of seed intoareas where it is not intended to be placed.

Following topdressing and seeding, acarpeted dragmat or brush should be usedto smooth and work the sand/seed mixtureinto the putting surface. Care should betaken during this operation not to drag theseed out past the intended boundaries ofthe green.

Tips for Optimum Seed Establishment

At the time of planting, the greens shouldreceive a starter fertilizer with a ratio ofnitrogen, phosphorus, and potassium in the1-2-1 or 1-2-2 range. Phosphorus should besupplied at approximately 0.5 to 0.75 poundsper 1,000 square feet, as this essential nutri-ent is vital to good seedling growth.

To promote good seed establishment atthis critical time, soil moisture conditionsshould be maintained at optimum levelswithout creating localized dry spots or over-wet conditions. The surface of the over-seeded greens should be kept uniformlyand consistently moist during the initial two-week germination and establishment period.Manual irrigation may be needed during theearly stages to minimize undesirable lateralseed movement.

Naturally, scouting for disease takespriority at this time as well. A preventativefungicide program should be scheduled tominimize disease outbreaks. Furthermore, itis suggested to utilize a fungicide-treatedseed to prevent "damping off' during thecritical seed germination stage.

Usually, a major issue during the firstmonth following overseeding is the heightof cut. To promote optimum seedling estab-lishment at this critical time, heights of cutin the range of JSzto 'l'l6 of an inch are recom-mended. Maintaining these heights of cutfor at least four to six weeks is essential toencourage deep root development for anoverall healthier overseeded turf. Be sure tomaintain razor-sharp mowers at this timeand, if possible, mow when the surface ofthe green is dry to minimize damaging orpulling out the immature grass seedlings. Itshould be understood, however, that whenutilizing perennial ryegrass as the predomi-nant overseeded turf, its rapid growth rateduring the initial two to three weeks ofestablishment gives the appearance that amuch higher height of cut is being main-tained. Stick to the program. If a lower height

of cut is used for the sake of green speed,problems may be encountered in achievinggood turf establishment. If the issue is amajor one, try mowing twice per day tomaintain peace. Once the overseeded turfhas become well established, gradual lower-ing of the height of cut can be performed toachieve the desired speed and play charac-teristics of the overseeded greens.

Maintaining Optimum PuttingQuality During the Season

Cutting height always seems to be at theforefront on this issue as well. As mentionedpreviously, cutting height should not becompromised during initial establishment.Once the turf is established, however, mow-ing heights in the range of Y3zto YI6 of aninch can be maintained during this relativelycool period. On well-constructed greenswith minimal play, mowing heights as lowas VBinch have been practiced with success.Mowing overseeded bermudagrass turf atthis low level, however, should be done onlyfor short periods of time and should belimited to Tifdwarf-based greens overseededwith bent or a combination of bent and Poatrivia lis in the southernmost regions of thecountry. It cannot be overemphasized thatpracticing these extremely low heights ofcut places a significant amount of stress onboth the overseeded grass and the basebermudagrass as welL

Instead of reducing the mowing height toachieve the desired putting characteristics,surface grooming, light topdressing, orrolling can be used. Very light verticalmowing or, preferably, occasional groomingin conjunction with routine mowing is anexcellent method to produce good winterputting characteristics. Use of groomers dur-ing regular mowing is an efficient methodto promote upright growth and smooth ballrolL

Light topdressing every four to six weeksduring the winter season also is effective inproducing desirable putting characteristicson overseeded greens. The use of approxi-mately 0.1 to 0.3 cubic yards per 1,000square feet is recommended. When uni-formly applied and lightly brushed in, golferswon't be inconvenienced, but putting qualitywill be improved.

Should high-traffic areas begin to exhibita loss of turf density during the height of theseason, corrective measures should be taken.If these thin areas persist, problems withalgae formation on the surface of the greensmost likely will be encountered.

To promote turf recovery in high-trafficareas and minimize the development ofalgae, practices such as spiking, W' solid-tine aerification, or water injection cultiva-tion should be performed. Spiking works

To ensure seed-to-soil contact, the bermudagrass must be adequately renovated prior to seeding.Here, a Lely dethatcher is used at Augusta National G.C., Augusta, Georgia.

well when thinning is minor, but in areaswhere significant turf thinning is occurringfrom intense traffic and over-wet soil con-ditions, solid-tine aerification is recom-mended.

Water injection aerification is a goodtool to provide improved oxygen infiltrationdeep within the profile, and due to its methodof operation there is very little disruption tothe surface of the turf. In fact, any of thesethree cultural practices can be performedwhenever necessary, with little or noinconvenience to the golfer.

To further assist in the rapid recovery ofturf density in isolated problem areas, sup-plemental seeding also is suggested. Handapplication of a sand/seed mix immediatelyfollowing light surface preparation is advan-tageous in facilitating turf recovery.

A very effective method of preparingisolated thin areas for seeding was devel-

oped by Bill Henderson at the WellingtonCountry Club. His staff makes use of an oldgroomer reel attached to a rotary mowerhandle to prepare the surface. No heavyequipment is needed, and this procedurecan be performed effectively by one crewmember.

Tips for a Smooth Transition

Now that you've made it successfullythrough another busy winter play season,your work continues. All the procedurescarefully executed over the past five to sixmonths to maintain a good overseeded turfcover now must be somewhat reversed tofacilitate a smooth transition back to thebase bermudagrass. Following is a con-densed list of procedures that will be helpfulin your efforts to complete a smooth springtransition program.

The spring transition program is governedby soil temperatures, just as it was with falloverseeding. Soil temperatures should bemonitored closely, and when the temperatureof the root zone at a 4-inch depth stabilizesabove 64 degrees Fahrenheit, the followingspring transition practices should be initiated.

• Groom or lightly verticut one to twotimes per week

• Gradually lower the height of cut toapproximately %2"

• Increase soluble nitrogen fertilization• Maintain good soil moisture• Initiate spring/summer aerificationpractices

The information contained in this articleshould be of benefit to help you succeed withfuture overseeding programs. Of all thingsdiscussed, remember that only one thing iscertain: Mother Nature ultimately determinesthe outcome.

SEPTEMBER/OCTOBER 1993 5