Effective Turfgrass Weed Controlby A. THOMAS PERKINS, I.nstructor in Agronomy, Pennsylvania State University

A dvancing technology has touched all fields ofendeavor. The science of turfgrass managementis no exception.

One obvious example is in the area of weedcontrol. The increasing number of herbicidesnow available to turfgrass managers has re-sulted in their unconscious addition of one wordto the topic of weed control. That one word is"chemical."

In some respects this can be viewed as anunfortunate development, based on the fact thatmany people use chemicals as a panacea forweed problems. They fail to place herbicides intheir proper perspective.

Herbicides are just one of the many usefultools that can be incorporated into an overallmanagement program based on the applicationof sound agronomic. practices designed to pro-

vide the best possible conditions for growingturfgrasses. With these thoughts serving as aguideline, a review of today's weed problemsand some of the more useful herbicides is inorder.

If documented proof of the importance ofweed control problems were needed, the 1966Pennsylvania Turfgrass Survey has providedmore than enough. A review of the weed relatedsections in that report shows that weeds are theNo. 1 turfgrass problem when all turfgrass areas(home lawns, parks, cemeteries, golf oourses,etc.) are combined. Weeds rank as the secondmost troublesome problem on golf courses, themost intensively maintained turfgrass areas.Narrowing the field of possible weed pests down,the survey reports that golf oourse superinten-

30 Ibs. ail A of bensulide - 6 ft. wide darker gr een strip across 16 strains of bentgrass - colordifference due to absence of Poa.

Closeup of control plot of crabgrass (left) and 9 Ibs. siduron ail A {right} treated and seededMay 27 - picture June 15.

dents ,ranked their weed problems as follows:1. Poa annua 24.3%2. Knotweed 22.1%3. Grab grass 21.0%4. Broadleaved Weeds 18.4%5. Goosegrass 8.1%6. Miscellaneous Pests 6.1%

This list provides an excellent basis for adiscussion of turfgrass herbicides, since themajority of weed control research has been de-voted to one or another of these species.

CRABGRASS

This annual pest has ,received the greatestattention from researchers because of its wide-spread and continual occurrence.

Crabgrass control has envolved to the pre-dominant use of highly selective pre-emergentchemicals. These chemicals must be of sucha nature that when applied to an area they stayin place to afford maximum levels of controlover an extended period of crabgrass germina-tion. This same characteristic has also elimin-ated many promising chemicals from commonuse, because their excessive immobility in thesoil has resulted in residual toxicity to somedesirable turfgrass species. Additionally, thetrend today is towards dry formulations of thesematerials. These dry products offer not onlyease of application but also a generally higherlevel of control than their sprayable counter-parts.

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If crabgrass control were the only criterionfor recommending a particular chemical, analmost endless list of materials could be pre-sented. Certainly this isn',t the case, and thesafety of these chemicals on the variousturfgrass species weighs heavily on their finalselection. Not all recommended chemicals aresafe on aII turfgrasses but at Ieast one materia Iis suitable for every situation. An examinationof the recommendations of the experimentstations in the Northeast would yield a com-bined list such as follows:

1. H-95732. Benefin3. Bensulide4. DCPA5. Siduron

A more detailed discussion of thesematerials is necessary to understand their bestusage potential.

H-9573 (Azak) should be limited to infre-quent use on bluegrass turf. It has showndefinite injury to both the fine leaved fescuesand to the bentgrasses. In a continued programof crabgrass control, H-9573 has shown residualtoxicity even to bluegrass. Crabgrass control ingeneral is good to excellent. (90% or better).

Benefin (Balan) is a relatively new materialon the 'crabgrass market and still requires moreexamination. Its performance to date, particu-larly with regards to injury, has ,been inconsis-tent. Injury to bentgrass and fescue has

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occurred and a few reports of bluegrass injuryhave appeared. Nonetheless, crabgrass controlis good to excellent and final conclusions haveyet to be dr,awn.

Ben-sulide (Betasan or Presan) finds itsprimary use on bentgrass turf due to Us highlevel of safety on most of these sensitivespecies. Control results have been good toexcellent.

DOPA '(Dacthal) has consistently given thebest performance on bluegrass turf over aperiod of about ten years. It can be injuriousto bentgrass and usually does cause injury tored fescue turf. In addition to its excellent con-trol of crabgrass, DOPA is the only herbicidewhich shows an acceptable consitency in con-trolling goosegrass. Although goosegrass is notas widespread as crabgrass, it usually requiresa more concentrated program to achieve satis-factory control.

Siduron (Tupersan)is a rather elite memberof t,he crabgrass herbicide group. This chemicalcan be applied at the time of establishmentand provide an excellent level of crabgrasscontrol while not affecting the germination ofthe desirable grass species. It is equally effec-

tiveon mature turf stands and is consideredsafe on most turfgrass species with the exceptionof several vegetative bentgrasses.

With safety as an overriding criterion andthe average user in mind, the PennsylvaniaState University now recommends three of theabove materials for ,crabgrass control. They areas follows:

BensulideDCPASiduron

ANNUAL BLUEGRASS

Annual bluegrass or Poa annua has longbeen a weed problem on highly maintained,well irrigated areas. Selective control measureshave been 'attempted for years but little successachieved. Chemical control of Poa annua in-volves two areas of major concern, (1) injuryto permanent grasses and, (2) residual toxicityas it affects subsequent reseeding operations.Two of the chemicals currently being tested forpre-emergence control of Poaannua 'are calciumarsenate and bensulide.

Calcium arsenate has been somewhat erraticin its performance. Control results have ranged

Knotweed control with dicamba. Near solid stand of knotweed. Plot on left not treated. Plot onright treated pre-emergence spray.

from poor to excellent with unpredictable de-grees of bentgrass injury. The ever presentphobia of handling arsenicals plus this inconsis-tency have resulted in increased effort to findother chemicals for this problem. The mostpromising material is bensulide. Research todate has shown that pre-emergence controllevels are good to excellent while no permanentsurface injury has appeared. Temporary dis-coloration during periods of spring moisturestress followed by differential patterns of sum-mer wilting have been observed. These factorswould suggest a possible root pruning effect,but more detailed study is needed before posi-tive statements can be made.

Successful reseeding following herbicideapplication may also cause some difficulty. Onareas containing a fairly uniform distributionof Poa annua where its density isn't excessive,reseeding shouldn't be necessary. For areasrequiring reseeding, success depends on beingable to place the seed in contact with the soilbelow the surface herbicide layer. Greatestsuccess in this respect has been obtained usingmechanical grooving equipment.

With difficulties such as these still to besolved, the annual bluegrass problem may bewith us for some time to come. Nevertheless,the performance of bensulide to date offersconsiderable hope that it may soon be recom-mended for incorporation ,into an overall Poaannua control program.

BROADLEAF WEEDS

This rather large grouping of weeds containsthe remainder of our major weed problems.Chemical control within this group involves twostages of turfgrass maturity.

Mature TurfFor many years, broadleaf weed control on

mature turf meant 2,4-0 or one of its closelyrelated derivatives. The addition of several newherbicides to this market have eliminated manyof our most troublesome broadleaf weeds asserious problems.

Oicamba provides a reliable control formature knotweed, white clover, and many of theweeds which were formerly classified as difficultto kill with 2,4-0. Mecoprop allows treatmentof the close cut bents without fear of temporarydiscoloration or permanent injury. Beyond itssafety benefits it offers excellent control of

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loxynil at ~ lb. ail A srayed across 4 seededstrips in early post emergence condition. Barearea was seeded to mixture of broadleafannual weeds, shows complete control. Threegrass species were able to develop intoacceptable stands. Seeded August 30, treated

September 17. Picture October 1.

white clover and chickweed.With this trio of chemicals to work with, the

major emphasis in the past several years hasbeen to develop a combination product whichoffers a much broadened spectrum of control.This has been achieved by combining 2,4-0 anddicamba in <ratios of approximately 4:1. Theresults from such combinations have beenexcellent and we can now eliminate most, ifnot all, of our broad leaf weed problems with asingle preparation.

One 'important factor should be understoodabout 2,4-0 - dicamba mixes. When these mixesare being formulated as dry materials, the2,4-0 rate of application must be adjustedaccordingly. To be on a level with liquid treat-ments, dry 2,4-0 must be applied at two tothree times the rate of the normal liquidapplication. This factor is essential in deter-mining the effectiveness of dry combinationsof 2,4-0 and dicamba.

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control in seedling turf.It should be apparent from the preceeding

discussion that sufficient management tools, inthe form of herbicides, now exist to enable anycompetent turfgrass manager to control mostif not all of his weed problems. The fact thatweeds still remain the problem they are todaypoints once again to the view that herbicidesare considered by too many people to be cure-ails and not as one management tool in awell-conceived and well-executed managementprogram. Professor H. Burton Musser has ex-pressed this sentiment adequately: "Weedencroachment is the result and not the causeof poor turf."

Generic and trade names of common turf-grass herbicides:

Generic Name Trade Name

Despite manufacture emphasis on drymaterials, it remains a fact that liquid prepara-tions of these same two chemicals offer themost effective control over the widest rangeof broad leaf weeds. A noteworthy aspect of suchcombinations is that increasing their wettingproperties offers definite control advantages.

Seedling TurfShort of fumigation, seedbed control of

broad/eaf weeds has been nonexistent. With2,4-0 as the major herbicide a minimum treat-ment delay of six weeks was required. Even atthis stage the risk of considerable stand re-duction was present.

Two experimenta I materia Is, bromoxyn i I andioxynil, now under test show promise for thistroublesome area of weed control. Results atPennsylvania State University show successfulstands of red fescue, bluegrass, and bentgrasscan be achieved following early post-emergencetreatment with these two materials. As expected,red fescue and bentgrass are more susceptibleto injury than bluegrass. A wide range of com-mon seedbed weeds such as pigweed, lambs-quarter, mustard, ragweed, chickweed, andyellow rocket were effectively controlled withboth herbicides.

Additional study with these materials is inprogress, but results to date would indicate thateither or both of these chemicals may alleviatesome of our present difficulties with weed

Benefln

BensulideBromoxynilCalcium arsenateDCPADicambaH-9573loxynilMecopropSiduron2, 4-D

BalanBetasan or PresanBrominalVarious namesDadhalBanve/-DAzakNone (Experimental)

MCPP, MecopexTupersanVarious names

Establishment control of crabgrass with siduron - 22 days after treatment. Six strips of grassseeded the same day siduron was applied. Strip left to right - Merion, Col. Bent, Crabgrass,Kentucky Bluegrass, Red Top, Creeping Red Fescue. Crabgrass completely controlled with afftreatment rates 4% Ibs. ai / A - 9 Ibs. - 13% Ibs. - 18 Ibs. Occasional blocks of crabgrass are

control plots.