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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FIELD SCIENCE

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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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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