PREFACE TO CHAPTER 6. Various turf management activities may influence weed population dynamics and

Transcription

1 PREFACE TO CHAPTER 6 Vrious turf mngement ctivities my influence weed popultion dynmics nd interfere with weed control. A iohericide pproch could e enhnced if comined with culturl mngement prctices. Mowing is mechnicl stress tht could differentilly ffect weed communities nd select certin weed species. Repeted mowing could chnge weed species composition nd undnce. Weed shifts towrd more tolernt popultions to certin chemicl nd culturl prctice re mjor mngement concerns. In Chpter 6, the sme two field study sites mentioned in the previous chpter were monitored for two yers to investigte the effect of mowing heights, in comintion with the S. minor iocontrol nd the stndrd chemicl hericide, on the popultion dynmics of dndelion nd other rodlef weed species nd the impct on turf qulity. The results of Chpter 6 hve een prepred in mnuscript form to e sumitted to the Journl of Plnt Interctions. The mnuscript is co-uthored y Professor Aln K. Wtson, my supervisor. I designed the experimentl set-up, performed the experiments nd the sttisticl nlysis, nd wrote the mnuscript. Professor Wtson supervised the work, provided finncil nd technicl resources, nd corrected the mnuscript. 113

2 CHAPTER 6 Impct of mowing nd weed control on rodlef weed popultion dynmics in turf. MOHAMMED H. ABU-DIEYEH & ALAN K. WATSON Deprtment of Plnt Science, McGill University, 21,111 Lkeshore Rod, Ste-Anne-de-Bellevue, Queec, Cnd, H9X 3V9 114

3 6.1. Astrct 1. Turfgrss is mn mde setting dversely ffected y common dndelion (Trxcum officinle) nd other rodlef weeds. Control of these weeds in temperte turfgrss hs een redily chieved with phenoxy nd like hericides. The hericide option hs een revoked through municipl nd provincil legisltion in mny regions of Cnd, necessitting the need for lterntive pproches. 2. Vrious turf mngement ctivities my influence weed popultion dynmics nd interfere with weed control. The effects of iocontrol gent, Sclerotini minor, chemicl hericide, Killex, nd defolition stress t three different mowing heights on rodlef weed dynmics were exmined in two turfgrss stnds for two consecutive yers. 3. Mowing did not reduce the verge or the monthly popultion densities of dndelion or the percentge ground cover of rodlef weeds. In the second yer, mowing significntly reduced the density of white clover (Trifolium repens), ut significntly incresed rodlef plntin (Plntgo mjor), prticulrly t the closest mowing height (3-5 cm). 4. Aprt from the 3-5 cm mowing height, no differences in efficcy were otined etween the S. minor nd Killex tretments on the densities of dndelion, white clover, rodlef plntin, nd prostrte knotweed (Polygonum viculre). Common mllow (Mlv neglect) incresed in hericide treted plots nd other species including yellow woodsorrel (Oxlis strict), yellow todflx (Linri vulgris), nd lmsqurters (Chenopodium lum) incresed in undnce in plots mowed t the closest height (3-5 cm) nd in plots treted with Killex. 115

4 5. The reduction in dndelion densities nd percentge rodlef ground cover one month fter Killex ppliction persisted throughout the study period, unffected y mowing height except in Septemer of the 1 st yer when the density of dndelion ws significntly greter t the 3-5 cm mowing height compred with the other heights. Significnt differences etween Killex nd S. minor tretments on dndelion popultion dynmics were rrely present nd did not fvour either tretment. After S. minor tretment, turf qulity grdully improved over the study period t oth sites with lower vlues t the 3-5 cm mowing height. There were no signs of dmge to the grss species due to repeted S. minor tretments. Similrly, Killex tretment improved turf qulity even t the 3-5 cm mowing height, ut grss dmge in three out of 12 plots ws followed y smooth crgrss (Digitri ischemum) invsion. 6. The S. minor (IMI ) formultion comined with regulr mowing t ~ 7 cm ws s effective s Killex for rodlef weed suppression. Keywords: Trxcum officinle, common dndelion, Sclerotini minor; weed popultion dynmics, turfgrss, iologicl control. 116

5 6.2. Introduction Weeds re symptomtic of wekened turf, not the cuse of it (McCrty et l. 21). Weed growth occurs in turf under dverse environmentl conditions nd when the soil hs een exposed or distured y compction, plnting, or mintennce ctivities (McCrty et l. 21). Mowing is the most sic turfgrss culturl prctice nd ffects most other culturl opertions (Turgeon 1985). Mowing is stressful to turfgrss, removing much of the photosynthesizing tissues leding to exhustion of crohydrte reserves during regrowth (Fry & Hung 24). The exct tolerted mowing height for specific turfgrss is difficult to predict ecuse it is result of interctions etween turfgrss genotype, climte, culturl prctices, time of the yer, nd other environmentl influences (Turgeon 1985; Fry & Hung 24). As consequence of mowing, popultion undnce nd diversity of weeds my chnge nd crete new competitive environments mongst existing weed species nd etween the crop (turfgrss) nd the weeds (Busey 23). Prctices tht fvour crop growth will generlly disfvour weed undnce (Rdosevich et l. 1997). Culturl mngement prctices hve een used to control weeds in turfgrss for some time nd relince on culturl mngement to control turfgrss weeds my reduce dependence on synthetic pesticides (Busey 23). Hericides, like 2,4-D (2,4-dichlorophenoxy cetic cid) nd three-wy mixes of 2,4-D + mecoprop ((±)-2-(4-chloro-2-methylphenoxy) propnoic cid) + dicm (3,6- dichloro-2-methoxyenzoic cid) hve een widely used to control rodlef weeds in turfgrss. However, hericide use on lwns hs come under severe pressure from environmentl nd pulic helth perspectives (Roins & Birkenhlotz 23), resulting in 117

6 vrious levels of government encting legisltion inhiiting or nning the use of pesticides in urn res (Riddle et l. 1991; Schnick et l. 22; Cisr 24). In response to hericide use restrictions, good mngement prctices re eing promoted nd lterntive pproches including iologicl re eing reserched (Neumnn & Bolnd 22, Stewrt-Wde et l. 22, Zhou et l. 24). Sclerotini minor Jgger is n Ascomycete with suppressive effects on dndelion nd other rodlef weeds in turfgrss systems (Ciotol et l. 1991, Riddle et l. 1991, Brière et l. 1992, Schnick et l. 22, Stewrt-Wde et l. 22, Au-Dieyeh & Wtson 26: Chpter 5). Severl uthors (Burpee 199; Kennedy & Kremer 1996; Rdosevich et l. 1997; Cousens & Croft 2) hve emphsized the importnce of studying the ecology nd popultion dynmics of weeds to enhnce weed iocontrol progrms. In generl, ny weed control method removes or suppresses trgeted species, ut this ctivity my result in modifiction or disruption of the hitt of other orgnisms (Rdosevich et l. 1997). Therefore n ecologicl pproch rodens mngement options nd decreses the proility of filure (Booth et l. 23). Comining fungl pthogen with defolition hs een shown to increse suppressive effects on weeds, compred with the pthogen lone (Green et l. 1998; Kluth et l. 23). In this study, interctions etween mowing heights nd two different control strtegies, common three-wy mix hericide, Killex, nd iologicl control, S. minor, on the popultion dynmics of dndelion nd other rodlef weeds were investigted. The field experiments were conducted for two yers in two lowmintenned turf environments. 118

7 6.3. Mterils nd Methods The fungus formultion Sclerotini minor (IMI ) ws isolted from disesed lettuce plnts (Lctuc stiv L.) from south western Queec nd the stock culture ws mintined s scleroti t 4 o C. The myceli of the germinted scleroti were used to inoculte utoclved rley grits ( mm dimeter) s descried in Au-Dieyeh nd Wtson (26: Chpter 5). S. minor grnulr formultions were freshly prepred two weeks prior to tretment ppliction. Viility nd virulence of the fungl inoculum were ssessed prior to use y plcing ten grnules from ech g on the surfce of PDA pltes nd nother ten grnules onto excised dndelion leves. The dimeter of colonies nd lesions cused y the fungus were mesured fter 24 nd 48 h of incution. Previous unpulished qulity control studies indicte vile tches to hve colony dimeters of 14-3 mm fter 24 h nd 4-7 mm fter 48 h nd virulent tches to hve n verge lesion dimeter >15 mm fter 48 h of incution Site description nd plot lyout design (see Au-Dieyeh & Wtson 26: Chpter 5) The field experiments were conducted in two different Sites on the Mcdonld Cmpus of McGill University, in Ste-Anne-de Bellevue, QC (45 o 25'N ltitude, 73 o 55'W longitude, 39. m elevtion). Ech field experiment ws conducted from My to Octoer for two consecutive yers. The climte dt for the yers of study re summrized in Tle

8 Study Site-1 (23-24 experiment) ws pproximtely 6 m 2 on lomy snd soil (corse snd = 9%, fine snd 73%, silt= 12%, cly= 6%) with ph of 7.15 nd 8% orgnic mtter. The lwn ws estlished in 1973 nd received low mintennce throughout its history except for repeted mowing during the growing seson (My to Octoer). The grss swrd ws pproximtely 6% Kentucky luegrss (Po prtensis L.), 3% perennil ryegrss (Lolium perenne L.), ptches of timothy (Phleum prtense L.), nd rre occurrences of nnul lue grss (Po nnu L.). The lwn flor ws highly diversified with 17 rodlef species oserved throughout the study period nd dominted y dndelion (Trxcum officinle Weer). Dndelion density ws 5-6 plnts m -2 prior to the spring tretment ppliction. Study Site-2 (24-25 experiment) ws locted in n open lwn re of pproximtely 6 m 2 tht ws estlished in 198 nd mnged with low mintennce. The turf t Site-2 ws superior in visul qulity compred with Site-1 with minly Kentucky luegrss (~9%) nd 1% red fescue (Festuc rur L.). Hericides hd not een pplied for the pst 1 yers nd the mjor rodlef species were dndelion (6-7 plnts m -2 ), white clover (Trifolium repens L.), nd rodlef plntin (Plntgo mjor L.). The soil ws lomy snd (12% corse snd, 75% fine snd, 7% silt nd 6% cly) with ph of 7.2 nd 6.6% orgnic mtter. Field experiments were estlished in My, one in 23 nd the other in 24, nd mintined until the end of Octoer of the following yers. The study sites (2 x 3 m) were mrked with metl posts nd plstic ropes nd the corners of ech plot were permnently mrked y wooden sticks to mintin plot integrity for the durtion of the study. The experimentl unit (plot) ws one meter squre with.8 m lleys etween 12

9 plots. The distnce etween ny two locks ws 2-3 m. The experimentl design ws split plot with four replictions. Mowing heights were the min plots nd weed control tretments were the suplots. The three levels of mowing heights, 3-5 cm, 7-1 cm, nd cm were initited two weeks prior to weed control tretment pplictions. Plots were mowed weekly, except for two weeks fter tretment, with gs powered rotry push mower. Grss clippings were returned during July nd August to ct s source of nitrogen (Kopp & Guillrd 22), ut removed during the six-weeks-post tretment periods to void cross contmintion etween locks. Four levels of weed control were imposed on 15-My nd on 15-Septemer t ech study site in ech yer ( totl of four pplictions per site) : 1) untreted control, 2) rodcst folir ppliction of Killex t 1.7 kg.i. h -1 (2 ml m -2 of.6% of originl concentrtion), 3) rodcst ppliction of 6 g m -2 grnulr formultion of S. minor, nd 4) rodcst ppliction of 12 g m -2 grnulr formultion of S. minor. The hericide ws rodcst pplied onto the grss surfce using 1.18 L vcuum spryer (Home nd Grden spryer. Model no RLF1-Mster Premium, Root-Lowell Mnufcturing Co, Lowell, MI). The S. minor formultion ws rodcst pplied using 2 ml plstic specimen ottle fitted with perforted lid (~1 mm dimeter) with suitle openings to pss the rley grits. If there ws no rinfll on the dy of ppliction or the grss ws not wet, the entire field ws sprinkler irrigted for two hours prior to lte fternoon tretment pplictions. No dditionl irrigtion or fertiliztion mngement ws pplied during the course of the study. The spring nd fll tretment ppliction dtes, My 15 nd Septemer 15, represent ner pek dndelion densities, 121

10 usul period for hericide ppliction, nd climtic conditions t these times re dvntgeous for the fungus Mesurements nd dt nlysis The numers of dndelions nd other rodlef weed species were counted in ech plot nd the percentge ground cover of rodlef weeds ws estimted in ech plot the dy efore the weed control tretments nd the lst week of ech month therefter. For white clover (Trifolium repens) the numer ws estimted y mesuring how mny 1 cm dimeter ptches of white clover covered the ground of plot. In ech monthly ssessment survey, turfgrss qulity ws lso visully ssessed using growth rting of -1 sed on comintions of color nd density where = no growth nd 1 = complete uniform turf (Johnson nd Murphy 1992). As the study sites re lowmintined turf, the cceptle visul qulity ccording to the used scle is 5%. Seson verge densities were lso clculted for species tht were presented uniformly etween the locks nd found continuously through the seson. Seson verge densities were clculted s n verge of the eight ssessments done in ech seson from My to Octoer including the two pre ppliction ssessments done in the mid of My nd Septemer. The rtionle for seson verge density vlues ws to ccount for the indirect effects due to new environments creted y the tretments, especilly chnges in grss ground cover nd vigour, nd to ccount for the species tht estlish fter spring tretments nd complete their life cycles efore the fll tretment in Septemer. Sttisticl nlyses were conducted using the SAS sttisticl pckge (SAS Institute Inc., Cry, NC, USA, 22). Monthly dt from the two field sites were sujected to 122

11 Levene test of SAS. Becuse of differences in environmentl conditions etween yers of study nd/or differences in turf estlishment etween sites most of the monthly dt from the two field experiments were heterogeneous, dt were not comined, ut nlyzed for significnce nd men comprisons seprtely. The 12 g m -2 S. minor tretment ws excluded from the dt nlysis of dndelion density, percentge ground cover, nd rodlef diversity s no significnt differences were otined in comprison with the 6 g m -2 tretment. Normlity for ech prmeter ws tested on model residuls using the Shpiro-Wilk test. Dt were nlyzed using GLM procedure of repeted mesures to determine the significnt interctions mong mowing heights nd different weed control tretments through time. Within ech yer of study, the pre ppliction nd post ppliction seson verge of dndelion density dt, seson verge density dt of other rodlef weeds nd seson verge turfgrss qulity dt were nlyzed using ANOVA for split plot design. A split-plot in time ws used to compre the densities etween the two yers. Differences in tretment mens were determined using Tukey's test t P = Results nd Discussion Turfgrss systems re mn-mde nd/or mn interfered environments. The undnce nd diversity of weed species in such systems re minly ffected y the history of culturl mngement prctices of the stnd, turfgrss species, nd climtic nd edphic fctors (Fry & Hung 24; McCrty et l. 21). Since mowing is necessity for ny turfgrss plnting, the exct tolerted mowing height is the fctor of interest rther thn mowing itself. We hve previously reported the effectiveness of comining the 7-1 or 123

12 12-15 cm mowing height with S. minor on reducing dndelion popultion densities t 2 nd 6 weeks fter ppliction (Au-Dieyeh nd Wtson 26: Chpter 5), ut in this twoyer-study, popultion dynmics of dndelion nd other rodlef weed species were monitored monthly in two sites to investigte the interctions etween mowing height nd the weed control tretments. Seventeen species of rodlef weeds were recorded in Site-1 with dndelion the dominnt species. White clover, rodlef plntin, common mllow (Mlv neglect Wllr.), prostrte knotweed (Polygonum viculre L.), yellow woodsorrel (Oxlis strict L.), yellow todflx (Linri vulgris Miller), lmsqurters (Chenopdium lum L.), nd irdsfoot trefoil (Lotus cornicultus L.) were uniformly dispersed over the study re ut with minor undnce (Tle 6.2). Other species listed in Tle 6.2 were occsionl or rre. In Site-2, the turf ws etter estlished, less diversified, nd dominted y dndelion followed y white clover nd rodlef plntin (Tle 6.3). Annul species such s prostrte knotweed nd lck medic (Medicgo lupulin L.) were oserved during July nd August in oth yers in untreted plots ut densities were negligile nd not reported Effect of mowing heights on weed dynmics In the sence of weed control, seson-long mowing t ny of the studied heights in the first yer of study did not reduce seson verge of dndelion popultion densities in the second yer (Tles 6.2 & 6.3), However, t the 3-5 cm mowing height, the seson verge dndelion density incresed in the second yer in study Site-1 (Tle 6.2). Moreover, t this close height pre nd post ppliction dndelion densities incresed in the 2 nd yer y 24-32% nd 15-44% respectively (Tle 6.4), indicting the dverse 124

13 impct of mowing t this height. The second yer seson verge density of white clover ws significntly less thn the first yer t ll mowing heights, ut rodlef plntin ws significntly higher, except t the cm mowing height (Tles 6.2 & 6.3). Popultion densities of other species including prostrte knotweed, yellow woodsorrel, nd mouseer chickweed (Cerstium fontnum Brumg.) incresed in the second yer in plots mowed t 3-5 cm (Tle 6.2). Mowing is stressful to plnts s it removes much of the photosynthetic cells nd exhusts the crohydrte storge reserves (Fry & Hung 24). But certin perennil weeds cn replenish root crohydrte stores very rpidly (Foster 1989; Donld 199) nd in some cses cuttings cn e dvntgeous for certin weeds s it removes the old nd ded tissues nd increses the new shoots (Oesterheld & McNughton 1991). Cutting of certin perennil weeds cn increse net photosynthetic rte, reltive growth rte, rnching or tillering fter relese from picl dominnce (Struss & Agrwl 1999). Different plnts respond differently to periodic mowing nd sufficient nd frequent cuttings re needed to prevent root reserves to e replenished etween cuts for certin perennils (Htcher & Melnder 23). In our study, perennil weeds responded differently to mowing, s mowing hd no impct on dndelion ut mowing significntly suppressed white clover. According to Wrwick & Briggs (1979) close mowing fvours short ecotypes or plnt species which hve the potentil to grow in rosette hit like rodlef plntin. These re similr to our findings s plntin incresed in the second yer in plots mowed t the closest height (3-5 cm) (Tle 6.3). Low mowing heights re lwys ssocited with more weeds (Busey 23) nd my chnge the species composition, undnce nd diversity (Meyer 125

14 & Schmid 1999; Crter et l. 2; Wilson & Clrk 21; Busey 23). This my explin the trend of incresing the coloniztion of more thn one species t the 3-5 cm compred with higher mowing heights (Tle 6.2). Regulr mowing t 2.5 cm every two weeks in other turfgrss environments (ufflogrss, entgrss, nd Bermud grss) did not control dndelion (Timmons 195). The close mowing t 3-5 cm reduced the seson verge dndelion popultion y 2% compred to other heights (7-1 & cm) (Au-Dieyeh & Wtson 26: Chpter 5), ut our results from this study indicted tht the reduction ws temporry nd occurred t the eginning of the study fter tht the popultion recovered or incresed (Tle 6.2). The replenishment of dndelion under the low mowing height ws due to continuous seedling estlishment (Au-Dieyeh & Wtson 26: Chpter 5) forming younger flt rosette hit popultion of dndelion more tolerted to close mowing. Defolition of dndelion y grzing or mowing increses the rosette rdius, decreses the root length, nd the plnt chnges from upright to flt growth form (Struik 1967). After grzing, dndelion lef density (numer of leves m -2 ) ws higher in short pstures thn tll pstures (Crlssre & Krsten 23). Those uthors explined this success of dndelion under short cnopies y incresing the overll meristemtic points in the protected lef xillry uds locted close to ground nd elow the grzing level nd this llows dndelion to tolerte close nd frequent defolition. A decrese in dndelion popultion density under incresing grss heights ws ttriuted to shding effects from the grss cnopy (Molgrd 1977). Shding incresed dndelion lef length nd specific lef re (the rtio of lef re to lef dry mss) nd due to this dndelion ws less susceptile to competition for light (Huglnd 1993). In our study no significnt reduction in the seson 126

15 verge dndelion densities occurred t the cm mowing height compred with the lower heights (Tles 6.2 & 6.3). Our results point out the dptility of dndelion rosettes to different mowing heights without mjor effects from close (down to 3 cm) to high (up to 15 cm) mowing levels. Perennil dndelions strted to regenerte from over wintered roots in April followed y high seedling recruitment s tempertures incresed with the dndelion popultion peking during My. The popultion then grdully declined reching its minimum during August (Figure 6.1). In Septemer, the lower temperture nd higher rinfll fvoured the grdul increse in density to form second pek t the end of the month. Susequently, the dndelion popultion density grdully declined under the effect of cooler tempertures (Figure 6.1). Dndelion ws the prevlent weed species in oth sites nd hd the highest percentge ground cover throughout the growing seson in ll untreted plots irrespective of mowing height (Figure 6.2). In untreted plots of Site-1, the verge numer of species per plot for the entire study ws 4.4 (verged over the two yers nd the four locks), with minimum of two reported in My nd June nd mximum of nine species reported in August while in Site-2 the verge ws 3.1 with minimum of two reported in My nd June nd mximum of five reported in July nd August. Mowing heights without weed control tretment hd no significnt effects on weed diversity. During summer months (July nd August) other rodlef weeds took the opportunity to flourish, minly nnuls like prostrte knotweed, lm s-qurters, shepherd s-purse, nd mouseer chickweed, ttining higher densities nd frequencies thn in other months. As result the highest rodlef weed diversity occurred during summer months when the 127

16 dndelion popultion ws t its minimum (Figure 6.3). This would e the result of the reduced competitive pressure from the dominnt species (dndelion) on other rodlef weeds. Turfgrss survive nd predominte in ecosystems with periodic defolition y fire, grzing, or mowing, ut mowing elow the tolernce level my e hrmful to turfgrss species nd give weeds competitive dvntge (Busey 23). In this study, mowing lone t ny level did not improve turf qulity t either sites in the two yers (Tle 6.5), which indictes tht turf qulity ws more determined y the level of weed infesttion rther thn regulr mowing t specific height. Close mowing my not e stressful to the present grss species ut my distur the competitive reltionship etween the intercting species nd/or increse light penetrtion throughout the thin cnopy nd consequently encourge certin rodlef weeds to germinte nd flourish. Mowing lone is not quick nd effective method of perennil weed control (Busey 23; Htcher & Melnder 23), ut comining mowing with nother control strtegy like hericide (Lowdey & Mrrs 1992) or pthogen (Kluth et l. 23) could e more effective Interctions etween mowing heights nd hericide tretment The common hericide, Killex, ws effective in controlling dndelion nd other rodlef weeds under ll studied mowing heights. Although the epinstic ending of dndelion leves nd florl scpes could e seen one week fter ppliction, the cler suppression of dndelion popultion ws not otined until six weeks fter ppliction (Figure 6.1). The effectiveness of 2,4-D, in Killex s folige hericide is determined y the sorption cpcity of the plnt cuticulr wx (Bker & Bukovc 1971) nd this my 128

17 slow the rte of its trnsloction prticulrly in well estlished dndelion popultion nd consequently postpone its effectiveness. A low popultion density of dndelion (less thn five plnts m -2 ) ws mintined until August of the first yer without significnt differences etween mowing heights. The surviving dndelions were minly those grown close to plot orders which might receive concentrtion of hericide ctive ingredient eyond the threshold vlue needed to kill dndelion. Dndelion hs een clssified s intermedite in susceptiility to 2,4-D due to the ility of older or well estlished plnt to tolerte it sed on the sorption cpcity of the cuticle (Bker nd Bukovc 1971). Six-weeks fter ppliction, only one to two seedlings recruitments were recorded (Au-Dieyeh & Wtson 26: Chpter 5) due to hericide persistence in the soil. 2,4-D persistence dt is highly vrile nd its hlf-life in soil vries from 2 to 296 dys nd could lst for one yer in grss clipping compost (Cox 1999). Treting dndelion with the hericide, when the popultion is in its reproductive stge, hd een shown to reduce germintion potentil to 4.8% nd 18.4% fter spring nd fll tretments, respectively (Au-Dieyeh et l. 25). Moreover the hericide tretment significntly reduced the dndelion seed nk (1 cm depth) compred with the untreted, control plots (Chpter 7). All the ove evidences indicted tht the low infesttion post to Killex TM tretment ws minly due to the killing effect of the hericide on dndelion seeds t lest in the superficil lyer of soil surfce. Since uried dndelion seeds re not le to germinte (Dunn & Moyer 1999), the August or Septemer recruits were minly new comers tht hd the ility to germinte in microsite on the soil surfce where the hericide ws prtilly or completely degrded. 129

18 In the second yer t Site-1 prior to the spring tretment pplictions, new seedling flush ws recorded with significntly higher density under the 3-5 cm mowing height (28-4 plnts m -2 ) compred with the 7-1 nd cm mowing heights (12-29 plnts m -2 ) (Figure 6.1). Ech of the pre nd post ppliction dndelion densities etween the two yers were significntly (P.1) reduced in the two sites without significnt effect from mowing height (Tle 6.4). However, the reduction ws the lest under the closest height (3-5 cm) only t Site-1, nd excluding this cse, the reduction in dndelion densities ws 7-98 %. Site-1 hd inferior grss estlishment nd less grss vigour thn Site-2 incresing the chnces of seedling estlishment, prticulrly into the more open grss cnopy under close mowing. Other studies suggested tht the estlishment of dndelion seedlings ws strongly inhiited in res of dense grss cover due to insufficient open ground nd light penetrtion (Molgrd 1977). Chnces of seedling estlishment re decresed 23 times in res with lush grss vegettion compred with open res (Ford 1981). Within ech site, no significnt differences due to mowing height occurred for monthly dndelion densities, percentge rodlef ground cover or even plot rodlef weed diversity. Importntly, strting from August of the first yer nd up to the following seson, the common mllow popultion density nd frequency significntly incresed in the hericide treted plots compred with S. minor or untreted plots without significnt effect from the mowing heights (Figure 6.4A). However the mllow density decresed significntly in the second yer in untreted nd S. minor treted plots (Figure 6.4A) minly due to seson-long mowing (Tle 6.2). In Site-1, other species like prostrte 13

19 knotweed, yellow todflx, yellow woodsorrel, nd lmsqurters flourished in hericide treted plots (Tle 6.2) nd consequently the percentge ground cover of rodlef weeds incresed during Septemer nd Octoer (Figure 6.2). This impliction is likely to e ecologiclly importnt s these species escpe or tolerte the hericide nd so could e cndidtes of co-dominnce or dominnce replcement of dndelion in turfgrss environments. The effectiveness of the hericide tretment in suppressing rodlef weeds resulted in significnt improvement in turf qulity t oth sites under ll mowing heights (Tle 6.5). Turfgrss generlly grows into the voids fter weeds hve een chemiclly controlled (Turgeon 1985), ut t Site-1 grss dmge ws oserved in three plots (out of totl of 12) during the summer of 23 nd ll the three plots were invded y smooth crgrss [Digitri ischemum (Schre.) Muhl.] (2-5 plnts per plot). Grss dmge nd Digitri invsion were not oserved fter hericide tretment in the superior qulity turf in Site-2 indicting tht grss with inferior qulity is sujected to crgrss invsion if more stress is encountered due to the hericide. The frequent use of 2,4-D s erly s 195 hd shifted cropping systems from rodlef weed to nnul grss domintion (Aldrich 1984) Interctions etween mowing heights nd iocontrol tretment Two weeks fter ppliction, the S. minor tretment ws more rpid nd cused significntly greter reduction of the dndelion popultion thn the hericide under ll mowing heights (Figure 6.1). Sclerotini minor is necrotrophic fungus cusing rpid collpse nd deth of infected plnts (Awi & Grogn 1979; Melzer et l. 1997) nd 131

20 requires high moisture nd temperture rnge of 5-25 o C to cuse disese (Melzer & Bolnd 1994). The different microenvironments creted y different mowing heights did not ffect the performnce of S. minor two weeks fter ppliction. Microenvironments cused y higher grss cnopies incresed disese incidence of certin turfgrss pthogens (Fgerness & Yelverton 21; Mrtin et l. 21), ut this is my e not the cse with necrotrophic iologicl control gent during periods with optiml environmentl conditions. Tretment dtes nd irrigtion (in cse there ws no rinfll) provided pproprite requirement for dndelion infection y S. minor negting possile mowing height effect. The effect of the S. minor tretment ws similr etween the two mowing heights (7-1 nd cm) in reducing dndelion popultion densities, ut it ws significntly less under the 3-5 cm mowing height. The incresed survivl of the dndelion popultion t the 3-5 cm mowing height level thn in the other heights ws minly due to more numerous nd erlier dndelion recruits nd to some regrowth (~ 2%) from undmged crowns of well estlished dndelions (Au-Dieyeh & Wtson 26: Chpter 5). Nturl dndelion popultions hve two peks per seson, one in My nd the other in Septemer, however, if the fvourle climte previl during summer due to rinfll, other flushes could occur due to the ility of dndelion seeds to germinte ny time during the growing seson (s reviewed y Stewrt-Wde et l. 23). Removing most of the dominnt weed species (dndelion) in plots treted with S. minor distured the re nd this siclly encourged weed seed germintion (Rdosevich et l. 1997). Soil in these plots ecme re with scttered ptches of grss llowing more sunlight to intercept the grss cnopy oosting dndelion seed germintion (Letchmo & Gosselin 132

21 1995; Noronh et l. 1997; Dunn & Moyer 1999). The vilility of growth resources in open cnopies my chnge the norml popultion fluctution due to frequent seedling recruitments. One month fter the first ppliction, new flush of dndelion seedlings ws oserved under ll mowing heights t oth sites, led to short popultion pek t the end of June (Figure 6.1). The mgnitude of dndelion recruitment ppered to e linked with the mowing fctor, site nd yer of study. Recruitment ws higher in the 3-5 cm high mowed plots compred to other mowing heights, nd higher in Site-2 s compred to Site 1. The totl monthly rinfll reported in June nd July of 24 (the first yer of site-2) ws out 2-fold the mount reported for the sme two months in 23 (the first yer of site-1) (Tle 6.1) nd this my explin why the recruitment size ws greter in Site-2. If summer conditions fvoured germintion, nother short pek my form t the end of August s hppened in Site-2 due to more frequent rinfll during July 24 thn in 23. Rinfll is expected to e requirement of seed germintion during the summer seson especilly in non-irrigted turf stnd. The flushes produced under the 3-5 cm mowing height were significntly greter in size thn those formed with other mowing heights nd mintined in greter vlues cross the second yer (Figure 6.1). Aprt from the 3-5 cm mowing height, the response of monthly dndelion popultion to S. minor tretment ws lmost similr to the hericide. Contrry to the hericide, S. minor hs no residul ctivity in soil nd higher densities under S. minor tretment re expected round the norml pek months of dndelion popultion. Using 7-1 or cm mowing heights, S. minor hd the sme effect like tht of the hericide in reducing the monthly diversity of rodlef weeds y 1-3 species per plot compred with 133

22 untreted plots (Figure 6.3) nd lso reduced the seson verge densities of the other two mjor competitive species white clover (Tles 6.2 & 6.3) nd plntin (Figure 6.4B). In ddition, oth hd the sme level of suppression on prostrte knotweed in the second yer (Figure 6.4C). The hericide ws significntly more effective thn S. minor in reducing percentge weed ground cover t the 3-5 cm mowing height. However, with the other heights (7-1 nd cm), superior reduction in weed ground cover occurred with the fungus in Site-1 nd the hericide in Site-2 (Figure 6.2). Unlike the hericide, S. minor tretment did not increse the popultion of other competitive species nd no grss dmge or crgrss invsion were oserved. The turf qulity of S. minor treted 7-1 or cm mowed plots improved grdully over the seson nd mintined cceptle qulity for the two yers (Tle 6.5). The strong iocontrol effect of S. minor on dndelion, white clover, nd plntin nd lso the decrese in undnce of other competitive species could minly e due to the direct pthologicl effect of the fungus nd/or the indirect effect exerted y the improved grss growth. In Chpter 4, our dt showed tht 32 rodlef weeds in turfgrss system were susceptile to S. minor infection if in direct contct with the rley-sed formultion of S. minor. Under S. minor tretment no chnges in species composition of rodlef weeds were oserved ecuse of the mowing heights ut chnges in the undnce of certin rodlef weeds were oserved t 3-5 cm grss height minly due to mowing t this low level rther thn the fungus. So tht species like prostrte knotweed, lmsqurters, nd mouseer chickweed were more likely to flourish during the seson (Figure 6.4D; Tles 6.2 & 6.3). 134

23 In conclusion, the ppliction of S. minor nd regulr, medium height (~7cm) mowing regime were highly effective in controlling rodlef weeds in temperte Kentucky luegrss turf. Tle 6.1. Wether dt for Ste-Anne-de-Bellevue, Queec during the yers of study 23, 24 nd 25. Environment Cnd Meteorologicl Dt. Ste-Anne-de-Bellevue Sttion. Temperture o C Reltive humidity ( %) Rinfll (mm) Month / yer Averge Min Mx Averge Min Mx Totl monthly My My My June June June July July July August August August Septemer Septemer Septemer Octoer Octoer Octoer

24 Tle 6.2. Seson verge popultion densities of rodlef weeds found in the plots t the study Site -1 during 23 nd 24. A = nnul; P = perennil; A, P = nnul or short-lived perennil. Within ech weed control tretment nd yer, mens with common letter re not significntly different t P =.5 ccording to Tukey s test. * Significnt t P =.5 nd ** significnt t P =.1 etween the two yers. Averge popultion densities (1) of rodlef weeds (no. plnts m -2 ) Species Life Yer of Untreted Killex (2) S. minor (6 g m -2 ) form study 3-5 cm Trxcum officinle P 1st cd 19cd 26 c 3c 17cd 15 d (Dndelion) 2nd 52* c** 5c** 7c** 31 1c* 1 c Trifolium repens P 1st c 3c 3.5c 8.7c 4.6c 3.3 c (White clover) 2nd 12* 4c* 8 1d 1d 2.2cd 3cd* 1.9d 1.8 d Plntgo mjor P 1st (Brodlef plntin) 2nd Mlv neglect P 1st (Common mllow) 2nd Polygonum viculre A 1st (Prostrte knotweed) 2nd Conzy cndensis A 1st (Cnd flene) 2nd Cichorium intyus P 1st (Chicory) 2nd Convolvulus rvensis P 1st (Field indweed) 2nd

25 Cerstium fontnum A, P 1st (Mouseer chickweed) 2nd Cpsel urs-pstoris A 1st (Shepherd's-purse) 2nd Oxlis strict P 1st (Yellow woodsorrel) 2nd Linri vulgris P 1st (Yellow todflx) 2nd Chenopodium lum A 1st (Lmsqurters) 2nd Lotus cornicultus P 1st (Birdsfoot trefoil) 2nd Amrosi rtemisiifoli A 1st (Common rgweed) 2nd Pyrrhopppus crolininus A, P 1st (Crolin flse dndelion) 2nd Medicgo lupulin A 1st (Blck medic) 2nd (1) Averge of the eight ssessments done from My to Octoer, including the two in the mid of My nd Septemer. (2) Brodcst folir ppliction t 1.7 kg.i. h

26 Tle 6.3. Seson verge popultion densities of rodlef weeds found in the plots t the study Site -2, during 24 nd 25. A = nnul; P = perennil; A, P = nnul or short-lived perennil. Within ech weed control tretment nd yer, mens with common letter re not significntly different t P =.5 ccording to Tukey s test. * Significnt t P =.5 nd ** significnt t P =.1 etween the two yers. Averge popultion densities (1) of rodlef weeds (no. plnts m -2 ) Yer of Untreted Killex (2) S. minor (6 g m -2 ) Species study 3-5 cm Trxcum officinle 1st (Dndelion) 2nd de** 1.3 e** 3 de** 22 c 8 d** 9 d** Trifolium repens 1st c 16.3 c 15.3 c 21.5 c 18.7 c 14 c (White clover) 2nd 12 ** 18.2 ** 17.9 ** 2.3 **.4 **.8 ** 4.6 ** 2 ** 1.2 ** Plntgo mjor 1st (Brodlef plntin) 2nd 6.2 ** 3.3 * c. c. c 1. c**.2 c*.3 c** (1) Averge of the eight ssessments done from My to Octoer, including the two in the mid of My nd Septemer. (2) Brodcst folir ppliction t 1.7 kg.i./h 138

27 Tle 6.4. Effect of mowing heights x weed control tretments on dndelion pre nd post ppliction densities over the two yers. Within the sme column, mens with common letter re not significntly different t P =.5 ccording to Tukey s test. * Significnt t P =.5 nd ** significnt t P =.1 etween the two yers. Dndelion popultion density (no. plnts m -2 ) Site-1 Site-2 Mowing Pre ppliction (1) Post ppliction (2) Pre ppliction Post ppliction () Height 1st 2nd % 1st 2nd % 1st 2nd % 1st 2nd % Tretment (cm) yer yer Differ. (3) yer yer Differ. yer yer Differ. yer yer Differ. Untreted * c cd cd c Killex cde -39cd 14cd 8c -46ef 47 1d** -97d 14c 4d** -73cd (1.7 kg h -1 ) f ** -7d 13cd 4c * -71f 6 1d** -98d 13c 2 ** -9cd ef ** -7d 19cd 5c ** -74f 53 2d** -97d 13c 3d** -74cd S. minor c -28cd 24c 3 27c c 25 19c -2 (6 gm -2 ) ef * -58 d 8cd 8c -3def 55 18c** -67d 17c 7d** -6cd cdef * -52cd 9d 7c -12cde 51 17c** -65d 14c 7d** -48c (1) dndelion density recorded in the ssessment done on the dy efore the spring (mid of My) weed control tretment. (2) the verge density otined from the six monthly ssessments (My-Octoer) done fter the spring tretment. (3) % Difference = (the two yers difference/1st yer density) x 1% 139

28 Tle 6.5. Response of turfgrss qulity, verged over the seson, to mowing heights x weed control tretments in the two study sites. Within the sme column, mens with common letter re not significntly different t P =.5 ccording to Tukey s test. A visul rnk scle of -1% ws used with % for no grss nd 1% for optimum grss qulity. Site-1 Site-2 Tretment Mowing Pretretment Posttretment Pretretment Posttretment Height (cm) Untreted e 11 d 4 31 e 23 e de 25 cd e 23 e e 29 cd de 26 e Killex (1) c 5 c c 1.7 kg.i./h cd cd Sclerotini minor cd 33 cd 46 5 cd 4 d 6 gm c c cd Sclerotini minor cd 35 cd 4 46 cd 47 cd 12 gm c

29 Figure 6.1. Effect of mowing height nd weed control tretments on dndelion density throughout the study period t the two study sites (1 & 2). Mowing heights were initited two weeks prior to spring tretment ppliction nd mintined throughout the experiment. Mowing heights were 3-5 cm (A), 7-1 cm (B), nd cm (C). Within ech grph, mens with common letter t ech time re not significntly different t P =.5 ccording to Tukey's test. Arrows indicte dtes of weed control tretment ppliction. Asterisks (*) refer to the ssessment conducted t the middle of the indicted month. 141

30 A-1 A-2 1 M* M J J A S* S O M* M J J A S* S O c Untreted Killex (1.7 kg.i h -1 ) S. minor (6 g m -2 ) c c c M* M J J A S* S O M* M J J A S* S O Dndelion density (No of plnts m -2 ) 8 8 B-1 B c c c c M* M J J A S* S O M* M J J A S* S O M* M J J A S* S O M* M J J A S* S O 8 8 C-1 C c M* M J J A S* S O M* M J J A S* S O M* M J J A S* S O M* M J J A S* S O 23 Site Site

31 Figure 6.2. Effect of mowing height nd weed control tretments on rodlef weed ground cover throughout the study period in the two study sites (1 & 2). Mowing heights were initited two weeks prior to spring tretment ppliction nd mintined throughout the experiment. The pplied mowing heights were 3-5 cm (A), 7-1 cm (B), nd cm (C). Within ech grph, mens with common letter t ech time re not significntly different t P =.5 ccording to Tukey's test. Arrows indicte dtes of weed control tretment ppliction. Asterisks (*) refer to the ssessment conducted t the middle of the indicted month. 143

32 Percentge rodlef weed groundcover M* M J J A S* S O M* M J J A S* S O M* M J J A S* S O M* M J J A S* S O 1 A-1 A-2 B-1 c Untreted Killex (1.7 kg.i. h -1 ) S. minor (6 g m-2) c c c c M* M J J A S* S O M* M J J A S* S O B c c M* M J J A S* S O M* M J J A S* S O C-1 9 C c 2 c c c 2 c 1 1 c M* M J J A S* S O M* M J J A S* S O M* M J J A S* S O M* M J J A S* S O 23 Site Site

33 Figure 6.3. Effect of weed control tretments on rodlef weed diversity throughout the study period in the two study Sites (1 & 2). Within ech grph, mens with common letter t ech time re not significntly different t P =.5 ccording to Tukey's test. Arrows indicte dtes of weed control tretment ppliction. Asterisks (*) refer to the ssessment conducted t the mid of the indicted month. Diversity of rodlef weeds (No of species m -2 ) Site-1 M* M J J A S* S O M* M J J A S* S O Untreted Killex (1.7 kg.i. h -1 ) S. minor (6 g m -2 ) Site-2 c c M* M J J A S* S O M* M J J A S* S O

34 Figure 6.4. Response of seson verge of popultion densities of different rodlef weeds to weed control tretments (A, B nd C) nd to mowing heights (D). Mowing heights were initited two weeks prior to spring tretment ppliction nd mintined throughout the experiment. Within ech grph nd ech yer, rs with common letter re not significntly different t P =.5 ccording to Tukey's test. * Significnt difference etween the two yers t P =.5. S. minor rte = 6 g m -2 ; Killex hericide rte = 1.7 kg.i./h. 12 A Mlv neglect 12 B Plntgo mjor 1 1 No of plnts m m n* m 2 n* n n* Untreted Killex S. minor Untreted Killex S. minor 12 C m Polygonum viculre 12 D Polygonum viculre 1 1 m No of plnts m n* n* n* 2 n* 2 Untreted Killex S. minor 3-5 cm 7-1 cm cm 146

35 6.5. Acknowledgments The uthors thnk Philippe Seguin for his vlule help in sttisticl nlysis nd lso Miron Teshler nd Yevgen Zolotrov for their help in field nd technicl work. Thnks re lso to Hshemite University, Zerk-Jordn nd to the Nturl Sciences nd Engineering Reserch Council of Cnd I2I nd Discovery grnts wrded to AKW for finncil support. 147