Canada Thistle (Cirsium arvense) and Pasture Forage Responses to Wiping with Various Herbicides 1

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1 Weed Technology Volume 19: Cnd Thistle (Cirsium rvense) nd Psture Forge Responses to Wiping with Vrious Herbicides 1 CHAD W. GREKUL, DAN E. COLE, nd EDWARD W. BORK 2 Abstrct: Weed-wipers my provide effective weed control while minimizing the ppliction of herbicide to nontrget species in rngelnd nd psture. To dte, few herbicides re recommended for use in weed wiping systems. We ssessed Cnd thistle nd non Cnd thistle herbge responses in two experiments in pstures, the first exmining wiped glyphoste, the second compring glyphoste with three brodlef herbicides t cost-equivlent concentrtions [on volume to volume (v/v) dilution bsis]. In both studies, wiping with glyphoste solution (33% v/v, equivlent to one to two dilution rtio of herbicide to wter) resulted in lower Cnd thistle density nd biomss thn check plots, with control lsting up to 2 yr. However, significnt reductions in grss biomss lso occurred nd were ssocited with n increse in the bundnce of weedy nnul forbs. In contrst, wiping with concentrted solution of clopyrlid (2% v/v), piclorm plus 2,4-D (20% v/ v), or 2,4-D plus mecoprop plus dicmb (24% v/v), resulted in similr levels of Cnd thistle control but no reduction in grss biomss. Despite direct ppliction of herbicides to tll weeds, clover species in mixed stnds were injured. In grss-dominted pstures, wiping with brodlef herbicides ws superior to nonselective glyphoste becuse the former more effectively blnced Cnd thistle control with the retention of grss production. Nomenclture: Glyphoste; clopyrlid; piclorm; 2,4-D; mecoprop; dicmb; Cnd thistle, Cirsium rvense L. # 3 CIRAR; clover, Trifolium spp. Additionl index words: Brodlef, herbge production, herbicide residue, legumes, weed density. INTRODUCTION Brodcst pplictions of herbicide re not widely used for weed control in psture nd rngelnd. Weedwipers hve been developed to selectively pply herbicide to weeds tller thn the desired species (Moomw nd Mrtin 1990; Wyse nd Hbstritt 1977). To dte, reltively limited informtion is vilble on the use of herbicide wipers in forge crops. Previous weed wiping reserch hs focused on brush control (Bovey nd Meyer 1989; Gibson et l. 1984; Myeux 1987; Myeux nd Crne 1984) nd herbceous weeds such s buckhorn plntin [(Plntgo lnceolt) L.; Welker nd Peterson 1989] or lefy spurge, [(Euphorbi esul) L.; Messersmith nd Lym 1985; Moomw nd Mrtin 1990]. Moreover, little reserch hs evluted the use of herbicides 1 Received for publiction December 5, 2003, nd in revised form October 2, First nd third uthors: Grdute Reserch Assistnt nd Associte Professor, Deprtment of Agriculturl, Food, nd Nutritionl Science, University of Albert, Edmonton, Albert, Cnd T6G 2P5; second uthor: Weed Specilist, Albert Agriculture, Food, nd Rurl Development, 2nd Floor, Agronomy Center, Street, Edmonton, Cnd T6H 5Z2. Corresponding uthor s E-mil: edwrd.bork@ulbert.c. 3 Letters following this symbol re WSSA-pproved computer code from Composite List of Weeds, Revised Avilble only on computer disk from WSSA, 810 Est 10th Street, Lwrence, KS pplied with wiper for Cnd thistle control (Krueger- Mngold et l. 2002). Cnd thistle is serious griculturl weed cross Cnd nd the northern United Sttes (Donld 1990; Moore 1975; Skinner et l. 2000). In Albert, s mny s 4 million h were infested in the 1960s (Alex 1966). More recently, Cnd thistle ws reported in 53% of ll Albert cerel nd cnol (Brssic npus L.) fields (Thoms et l. 1998). The few weed surveys of forge crops in western Cnd suggest this weed is lso mjor problem in psture nd hylnd (Thoms nd Wise 1983), s well s lflf (Medicgo stiv L.) seed fields (Goodwin et l. 1986). Effective herbicides for Cnd thistle control include piclorm, dicmb, or clopyrlid (Amor nd Hrris 1977; Donld 1990; Hggr et l. 1986; Moore 1975; Peterson nd Prochetti 1978), wheres 2,4-D nd MCPA re less effective (Amor nd Hrris 1977; Donld 1990). In Montn, Krueger-Mngold et l. (2002) found glyphoste pplied with wick pplictor controlled Cnd thistle in riprin res. Wiping with selective herbicides my mintin greter forge production thn wiping with glyphoste. Tller grsses nd desirble forbs tht grow intermixed with weeds my be injured becuse of the nonselective, sys- 298

2 WEED TECHNOLOGY temic nture of glyphoste. In these situtions, wiper ppliction of selective brodlef herbicides my cuse less dmge to shorter desirble species. However, the continued presence of chemicl residues in the soil from persistent herbicides my not be ltered with wiping (Messersmith nd Lym 1985), inhibiting the subsequent growth of desirble legumes (Hickmn et l. 1989). For exmple, residul effects on birdsfoot trefoil (Lotus cornicultus L.) hve been ssocited with the wiping of piclorm, clopyrlid, nd dicmb, wheres glyphoste nd MCPA did not ffect birdsfoot trefoil (Boerboom nd Wyse 1988). The overll utility of herbicides pplied with wiper depends on blncing the level of weed control ginst the ssocited injury to forge, either through direct ppliction or through herbicide residues in the soil. At present, no published dt exist on the effectiveness of sponge weed-wiper for controlling Cnd thistle with either selective brodlef or nonselective herbicides. Two sets of field experiments were conducted to investigte the effects of wiper-pplied herbicides on Cnd thistle bundnce nd ssocited psture forge production nd composition. The glyphoste experiment ssessed the effects of glyphoste pplied with sponge wiper t two different times of the yer, wheres the multiple herbicide experiment compred glyphoste with severl brodlef herbicides pplied using the sme sponge weed-wiper. MATERIALS AND METHODS Study Sites nd Experimentl Design. Experiments were conducted in pstures of the Aspen Prklnd region in centrl Albert from 1999 to 2001 (glyphoste experiment) nd 2000 to 2002 (multiple herbicide experiment), t four nd three sites, respectively (Tble 1). Ech site met the following criteri: (1) were reltively uniform in soils, disturbnce history, nd forge swrd composition, (2) hd hevy infesttion of Cnd thistle (e.g., 10 shoots/m 2 ), (3) were reltively free of other noxious weeds, nd (4) hd not been spryed for t lest 3 yr before All sites were dominted by some combintion of the following grss species: smooth bromegrss (Bromus inermis Leyss.), Kentucky bluegrss (Po prtensis L.), Cnd bluegrss (Po compress L.), quckgrss [Elytrigi repens (L.) Nevski], nd timothy (Phleum prtense L.) (Tble 1). Dominnt perennil forb species included dndelion (Trxcum officinle Weber in Wiggers), white clover (Trifolium repens L.) nd lsike clover (Trifolium hybridum L.), plus common yrrow (Achille millefolium L.). Pstures selected for the multiple herbicide experiment hd minimum initil clover cover of 10%. Common nnuls cross the sites included flixweed [Descurini sophi (L.) Webb.], wild buckwhet (Polygonum convolvulus L.), field pennycress (Thlspi rvense L.), common lmbsqurters (Chenopodium lbum L.), bll mustrd [Nesli pnicult (L.) Desv.], wild mustrd [Brssic kber (DC.) L.C. Wheeler], nd shepherd s-purse [Cpsell burs-pstoris (L.) Medic.]. Grzing by cttle occurred t ech study site before wiping to fcilitte height seprtion between the Cnd thistle nd forge stnd. Stocking rtes were typicl of the historicl grzing regime for ech psture bsed on the resident livestock opertion (Albert Agriculture 1981). Soils t ll sites were Typic Hplustolls (Orthic Blck Chernozems). Textures rnged from lom to silty-cly lom. Soil orgnic mtter levels vried from 9.3 to 14.6%, but nitrogen levels were low (mximum of 7 kg/ h) with no fertiliztion during the study. Soil phosphorus levels rnged from 7 to 160 kg/h, wheres potssium rnged from 395 to 1,883 kg/h. Soil ph vried from 6.6 to 7.3. Growing seson precipittion ws mesured t ech psture for ll yers of the study (Tble 2). The glyphoste experiment ws designed s splitblock, with timing of wiper ppliction s the whole plot fctor nd replicted wiping tretments in 1999 s the subplot fctor. The multiple herbicide experiment begn in 2000 using rndomized complete block design, with five tretments replicted four times t ech of three sites. Monitoring of tretment responses continued from 1999 to 2001 for the glyphoste experiment nd from 2000 to 2002 for the multiple herbicide experiment. Wiping Tretments. In the glyphoste experiment, glyphoste ws pplied to rndomly selected plots t two ppliction timings; sites 1 nd 2 were treted when the mjority of thistle plnts were t lte bud (July 27), wheres sites 3 nd 4 were treted when the mjority of Cnd thistle plnts were in lte flowering or seed dispersl (August 20 nd September 1, respectively). Wiping with glyphoste t the lbel recommendtion of 33% v/v solution (117 g i/l, obtined through one to two dilution rtio with wter) ws compred with n nontreted check. Plots were ech 3.5 by 15 m in size, nd replicted four times t ech site. Tretments in the multiple herbicide experiment were similr to those in the first becuse they consisted of n nontreted check nd plots wiped with glyphoste but were unique in tht they lso included wiped tretments of 2,4-D plus mecoprop plus dicmb, clopyrlid, s Volume 19, Issue 2 (April June)

3 GREKUL ET AL.: CANADA THISTLE AND FORAGE RESPONSES TO WIPING Tble 1. Loction nd vegettion chrcteristics for the psture sites used in the glyphoste experiment nd the multiple herbicide experiment s smpled in August of 1999 nd 2000, respectively. Site Loction Dominnt vegettion Initil thistle Grsses Forbs density b no./m 2 Glyphoste experiment 1 Brrhed N, W Quckgrss, Kentucky bluegrss, nd Dndelion Medow bromegrss 2 Lmont N, W Smooth bromegrss nd Kentucky Dndelion nd Common bluegrss yrrow 3 Spruce Grove N, W Cnd bluegrss, Smooth bromegrss, Dndelion nd Alsike clover nd Quckgrss 4 Thorsby N, W Kentucky bluegrss nd Timothy Dndelion nd White clover Multiple herbicide experiment 5 Edmonton N, W Kentucky bluegrss, Quckgrss, nd White clover nd Dndelion Smooth bromegrss 6 Morinville N, W Kentucky bluegrss, Quckgrss, White clover nd Dndelion Smooth bromegrss, nd Timothy 7 Wetskiwin N, W Kentucky bluegrss, Quckgrss, Smooth bromegrss, nd Timothy Alsike nd White clover, Dndelion Initil clover cover within the untreted check plots during 2000 for the multiple herbicide experiment t sites 5, 6, nd 7 were 14, 10, nd 36%, respectively. b Vlues re mens stndrd error, clculted from the check plots smpled. well s piclorm plus 2,4-D. In ddition, this experiment ws different thn the first in tht ll tretments were conducted during the erly-flowering stge of growth in erly to mid-august. At wiping, 15 to 30% of Cnd thistle stems were flowering, nd stems rnged in height from 10 to 150 cm. Wiping ws crried out t sites 6, 5, nd 7 on August 3, 4, nd 15 of 2000, respectively. Plots in this study were ech 3.5 by 10 m in size nd replicted four times per site. At the time of the multiple herbicide experiment, lbel recommendtions for herbicide concentrtion when wiping were vilble only for glyphoste. Other herbicide concentrtions were therefore determined by equting the commercil retil cost of the three brodlef herbicides with tht of glyphoste. This method (cost equivlency) kept results relevnt to prcticl weed control decision mking. The resulting herbicide wiper rtes Tble 2. Precipittion dt for the four sites of the glyphoste experiment ( ) nd the three sites used in the multiple herbicide experiment ( ). Experiment nd sites My August precipittion yr verge mm Glyphoste experiment Site Site Sites 3 nd Multiple herbicide experiment Sites 5 nd Site used bsed on v/v solutions of the commercil formultions diluted with wter were: (1) 33% glyphoste (117 g i/l), (2) 24% 2,4-D plus mecoprop plus dicmb (71 plus 19 plus 26 g i/l), (3) 2% clopyrlid (7 g i/l), nd (4) 20% piclorm plus 2,4-D mine (13 plus 48 g i/l). The wiper pplictor ws hnd-pushed, bicyclewheel mounted, grvity-fed, 3.4-m-wide sponge weedwiper. The sponge wiper ws mde up of four, 0.85-mlong cylindricl sponges ttched end-to-end long the length of the wiper br. All herbicide tretments were one-time pplictions. Wiping ws conducted bidirectionlly with sturted sponges in plots of ech of the experiments. In both experiments, grzed herbge between ptches of Cnd thistle ws generlly 10 to 15 cm high. The sponge of the wiper ws set t 30 to 40 cm, which llowed contct with the mjority of Cnd thistle stems while ensuring clernce of most grzed herbge. In the multiple herbicide experiment, seprte sponges were used for ech herbicide, nd the wiper herbicide delivery system thoroughly flushed with distilled wter between herbicides. Vegettion Smpling. Plots were not fenced t ny of the study sites, with cttle permitted to grze pstures throughout the study. However, in the 2 yr fter ppliction, two livestock exclusion cges (1.5 by 1.5 m) were rndomly plced in ech plot to prevent cttle grzing nd fcilitte mesurements of residul Cnd thistle nd forge biomss. 300 Volume 19, Issue 2 (April June) 2005

4 WEED TECHNOLOGY In the glyphoste experiment, live nd ded Cnd thistle shoot densities were ssessed 3 to 4 wk fter wiping in 1999 using four 0.5-m 2 qudrts in ech plot. Sites 1 nd 2 were smpled on August 19 nd 20, respectively, wheres sites 3 nd 4 were smpled on September 22. At pek stnding biomss in lte July of 2000 nd 2001, residul live Cnd thistle shoot densities were determined in four 0.5-m 2 qudrts within ech plot. Aboveground herbge ws smpled to ground level in single 0.5-m 2 qudrt in ech exclusion cge nd seprted into grss, forb, nd Cnd thistle biomss. All hrvested smples were oven-dried t 60 C to constnt weight nd recorded. In 2001, forbs were further seprted into nnuls nd perennils. Site 3 ws plowed t the end of 2000, eliminting it from the study. Exclusion cges were moved to new loctions in ech plot between yers. In the multiple herbicide experiment, 1 d before wiping t ech site in August of 2000, live Cnd thistle shoot densities were mesured in four 0.5-m 2 permnently mrked qudrts within ech plot. Posttretment live Cnd thistle densities were mesured in the sme qudrts on September 10, 2000, t site 7 nd on September 27, 2000, t sites 5 nd 6. At pek stnding biomss in mid-august of 2001 nd 2002, live Cnd thistle shoot density ws smpled in four 0.5-m 2 qudrts. In ddition, Cnd thistle, grss, nd forb biomss in 0.5-m 2 qudrt ws hrvested within ech exclusion cge to 2-cm height. Forbs were further seprted into nnuls nd perennils to ssess the residul effects of wiping on these vegettion components. Visul estimtes of percent cnopy cover of species composition, prticulrly legumes, were lso mde within ech plot. All hrvested smples were ovendried t 60 C to constnt weight nd recorded. Site 6 ws plowed in the spring of 2002 nd therefore not smpled tht yer. Dt Anlysis. Before nlysis, ll dt were checked for normlity through exmintion of the residuls nd testing with the Shpiro Wilks sttistic (SAS 1988). Post hoc men comprisons were performed on ll significnt tretments, on the bsis of significnt F-test results (P 0.05) using Tukey s method (P 0.05). In the glyphoste experiment, dt were subjected to split-plot ANOVA to evlute the effects of timing of tretment (whole plot), glyphoste wiping, s well s the timing by wiping interction (Steel et l. 1997). Forb biomss ws squre root trnsformed before nlysis to chieve norml distribution s required by ANOVA. Ech yer of posttretment smpling ws nlyzed seprtely becuse of the discontinuity in dt rising from the loss of site 3 in Initil tests of site by wiping tretment were generlly nonsignificnt (P 0.10) for the vribles exmined. Thus, dt from sites were pooled for finl nlysis. Thistle vribles nlyzed in 1999 included live Cnd thistle shoot density nd mortlity, where mortlity (%) (number of ded shoots/totl number of shoots) 100. Other vribles nlyzed in 2000 nd 2001 were live Cnd thistle shoot density nd biomss, s well s grss nd (non Cnd thistle) forb biomss. In 2001, nnul nd perennil forb biomsses were nlyzed seprtely. In the multiple herbicide experiment, ANOVA ws used to evlute herbicide tretment effects, with nlyses performed seprtely for ech yer to detect initil (2000) nd residul (2001 nd 2002) effects. Thistle density nd biomss were log 10 (Y 1) trnsformed before nlysis. Tests on site by tretment consistently indicted no significnt effect (P 0.10) of individul sites. Thistle vribles nlyzed in 2000 were live Cnd thistle shoot density nd Cnd thistle mortlity, where mortlity (%) [(number of pretretment live Cnd thistle shoots number of posttretment live Cnd thistle shoots)/number of pretretment live Cnd thistle shoots] 100. Thistle vribles nlyzed from 2001 nd 2002 were live shoot density nd biomss, wheres the forge vribles included grss, nnul forb, nd perennil forb biomss in 2001 nd totl herbge biomss (grss plus forb) in In ddition, legume cover ws nlyzed in RESULTS AND DISCUSSION Cnd Thistle Control. In the glyphoste experiment, the min glyphoste tretment in 1999 significntly ffected (P 0.01) ll Cnd thistle vribles in 1999, 2000, nd 2001, except biomss in the lst yer (Tble 3). Glyphoste ppliction incresed initil Cnd thistle mortlity in 1999 from 6 to 78% on verge nd decresed live Cnd thistle density by 68 to 80% during the 3 yr. Cnd thistle biomss remined lower in plots wiped with glyphoste for 2 yr, lthough in 2001 this difference ws not significnt (P 0.11; Tble 3). In 2000, Cnd thistle biomss on wiped plots ws only 24% tht of nontreted res. Within check plots of the glyphoste experiment, the generl decrese in Cnd thistle density from 41 shoots/m 2 in 1999 to 14 shoots/m 2 in 2001 nd the decrese in Cnd thistle biomss from 794 kg/h in 2000 to 136 kg/h in 2001 ws likely result of drought experienced in the ltter yer (Tble 2). Precipittion in the Volume 19, Issue 2 (April June)

5 GREKUL ET AL.: CANADA THISTLE AND FORAGE RESPONSES TO WIPING Tble 3. Cnd thistle mortlity, density, nd biomss in response to glyphoste wiping tretment nd timing by glyphoste wiping tretment combintions t four psture sites in centrl Albert from 1999 to 2001 (glyphoste experiment). Tretment df Density 1999 Mortlity Density Cnd thistle 2000 Biomss Density 2001 Biomss no./m 2 % no./m 2 kg/h no./m 2 kg/h Wiper tretment 1 P P P P P 0.01 P 0.11 Check 41 6 b Glyphoste 8 b 78 9 b 187 b 4 b 55 Timing by wiper tretment 1 P 0.01 P 0.02 P 0.07 P 0.03 P 0.95 P 0.43 Lte bud b Check 52 7 c 33 1, Wiped 6 c b 4 65 Seed dispersl Check 30 b 6 c b Wiped 10 c 68 b b 3 36 Mens clculted for untrnsformed dt. P vlues nd men comprisons re bsed on untrnsformed dt. Where pplicble, Tukey s test ws used for comprisons between tretments. Mens within column followed by different letters differ significntly (P 0.05). b Ech of the lte bud nd seed dispersl tretments ws conducted t two of the four study sites. spring nd erly summer of 2001 ws low compred with norml. Although more substntil precipittion fell in lte summer, low rinfll hd likely lredy impeded Cnd thistle growth by the time of vegettion smpling, nd similr to the conclusions of Boerboom nd Wyse (1988), my help ccount for the fvorble longterm thistle control we observed. Although conducted t different sites, wiping erlier t the bud stge of Cnd thistle growth in July 1999 resulted in greter Cnd thistle mortlity nd lower Cnd thistle density thn wiping lter t the seed-dispersl stge during August (Tble 3). However, there ws lso vrition in Cnd thistle response mong sites treted t the sme time, prticulrly biomss in 2000 (dt not shown), which my be prtly due to site-bsed differences in Cnd thistle bundnce. In prticulr, Cnd thistle density t site 1 (72 shoots/m 2 ; Tble 1) ws mrkedly greter thn ll other sites nd my hve incresed the likelihood of detecting tretment response. This response ws prticulrly pprent in 2000, t which time Cnd thistle biomss on plots treted with glyphoste remined lower (P 0.05) t site 1 only (1,785 nd 31 kg/h on check plots nd plots wiped with glyphoste, respectively). Our reductions in Cnd thistle from glyphoste re in greement with Boerboom nd Wyse (1988), who found tht 33% glyphoste pplied to Cnd thistle t the lte-bud to erly-bloom stge with ropewick pplictor reduced Cnd thistle up to 400 d fter tretment. However, Boerboom nd Wyse (1988) reported only visul Cnd thistle control (not shoot density or biomss) nd longer term responses (i.e., 2 yr or more fter tretment) were not determined. More recently, Krueger-Mngold et l. (2002) found tht glyphoste pplied nnully with wick pplictor t 1.5, 3.0, nd 4.5 kg i/h in Montn for 2 consecutive yr reduced Cnd thistle density nd biomss. In contrst, we found significnt reduction in Cnd thistle density 2 yr fter one-time glyphoste tretment. Results from this study nd tht of Krueger-Mngold et l. (2002) re difficult to compre becuse of differences in glyphoste rtes used. However, given the fvorble reductions found in this study, repeted wiper pplictions of glyphoste my not be necessry for longer term control of Cnd thistle in pstures. In the multiple herbicide experiment, the vrious herbicide tretments pplied with wiper resulted in significnt (P 0.01) effects on ll Cnd thistle vribles in 2000 nd 2001 (Tble 4). In 2000, ll herbicide tretments hd greter Cnd thistle mortlity nd lower live Cnd thistle shoot densities compred with nontreted plots (P 0.05). In ddition, wiping with glyphoste resulted in significntly greter initil Cnd thistle mortlity in 2000 thn 2,4-D plus mecoprop plus dicmb but did not differ from clopyrlid or piclorm plus 2,4-D. In 2001, only clopyrlid nd piclorm plus 2,4- D mintined significntly (P 0.05) lower residul Cnd thistle shoot density nd biomss thn the nontreted plots (Tble 4). By 2002, herbicides resulted in overll nonsignificnt effects on Cnd thistle density nd biomss (P 0.10), lthough trends similr to the yer before remined evident. Results from the multiple herbicide experiment re in greement with those of Boerboom nd Wyse (1988), who found tht in the yer of tretment, ropewick-pplied glyphoste, clopyrlid, nd piclorm provided better Cnd thistle control thn dicmb. The effectiveness of glyphoste, clopyrlid, nd piclorm on Cnd thistle control hve been ttributed to their rpid bsorp- 302 Volume 19, Issue 2 (April June) 2005

6 WEED TECHNOLOGY Tble 4. Cnd thistle mortlity, density, nd biomss in response to herbicide wiping tretments t three psture sites in centrl Albert between 2000 nd 2002 (multiple herbicide experiment). Wiping tretment Density b 2000 Mortlity Cnd thistle Density b Biomss b Density b Biomss b no./m 2 % no./m 2 kg/h no./m 2 kg/h P P P 0.01 P 0.01 P 0.18 P 0.26 Check c Glyphoste 4 b b 294 b ,4-D mecoprop dicmb 9 b 67 b 12 b 370 b Clopyrlid 9 b 72 b 8 b 130 b Piclorm 2,4-D 8 b 74 b 8 b 81 b Mens clculted for untrnsformed dt. Where pplicble, Tukey s test ws used to compre tretments. Mens within column followed by different letters differ significntly (P 0.05). b P vlues nd men comprisons of Cnd thistle density nd biomss re bsed on log 10 (Y 1) trnsformed dt. tion nd trnsloction through the plnt resulting in root kill (Boerboom nd Wyse 1988b; O Sullivn nd Kosstz 1984; Shrm et l. 1971; Turnbull nd Stephenson 1985). Moreover, brodcst folir-pplied clopyrlid nd piclorm re likely to provide longer term control through uptke from residue in the soil becuse of their longer soil persistence compred with glyphoste, dicmb, or 2,4-D (Herr et l. 1966; Vnden Born 1969). The results in this study indicte similr effect when these herbicides re wiped directly onto plnts, presumbly becuse of trnsloction to roots nd either exudtion into the soil or relese upon root decomposition (Hickmn et l. 1989; O Sullivn nd Kosstz 1984; Shrm et l. 1971; Vnden Born 1969). Although dicmb hs been shown in number of studies to provide greter efficcy thn 2,4-D for Cnd thistle control, it is generlly less effective thn glyphoste, clopyrlid, or piclorm (Boerboom nd Wyse 1988; Peterson nd Prochetti 1978). Although our results tend to support this rnking mong herbicides, no definitive differences in Cnd thistle mortlity, density or biomss were found mong the herbicides pplied here using sponge wiper. Our results lso suggest the effects of the one-time herbicide tretments hd begun to decline fter 2 yr, s evidenced by the lck of differences in Cnd thistle bundnce mong tretments during However, severe nd widespred drought t tht time my lso hve contributed to this through limited potentil for vegettive growth. The concentrtions of glyphoste, 2,4-D plus mecoprop plus dicmb, nd piclorm plus 2,4-D used in this study were comprble with the rtes used by Boerboom nd Wyse (1988). However, the concentrtion of clopyrlid used here (i.e., 2%) ws much lower thn tht of the forementioned study (10 nd 33%). Given the cost equivlency of the tretments used here, it ppers low concentrtions of clopyrlid nd intermedite concentrtions of piclorm plus 2,4-D my be the most pproprite for chieving longer term control of Cnd thistle in pstures with wiping. However, it should lso be noted tht Boerboom nd Wyse (1988b) found lower concentrtions of glyphoste (e.g., 2.5%) resulted in significntly greter Cnd thistle control thn higher rtes (e.g., 10 nd 33%). Greter glyphoste concentrtions were hypothesized to cuse more rpid tissue toxicity, which reduced trnsloction nd Cnd thistle control. It is therefore possible tht incresed trnsloction nd greter root mortlity my hve occurred t glyphoste rtes lower thn those of the lbel recommendtion tested in this study, in turn leding to longer term weed control. Forge Responses. Wiping with glyphoste in the glyphoste experiment hd significnt (P 0.05) effects on grss nd non Cnd thistle forb biomss 1 yr fter tretment (Tble 5), with wiped plots lower in grss but greter in forb biomss reltive to nontreted plots. Wiped plots hd 26% less grss production thn check plots in tht yer (Tble 5). Annul forb biomss lso remined visibly greter (i.e., by 734 kg/h; P 0.06) within plots wiped with glyphoste 2 yr fter tretment (Tble 5). There were no significnt timing by wiper tretment interctions (P 0.10) nd no significnt differences between sites (dt not shown). In the multiple herbicide experiment, grss biomss the yer fter tretment ws significntly reduced by wiping with glyphoste (P 0.05; Tble 6). Although wiping with brodlef herbicides incresed grss biomss reltive to the check (Tble 6), those differences were not significnt (P 0.05). Herbicide wiping tretment lso ffected the biomss of forbs (P 0.05), prticulrly nnuls. Glyphoste plots contined 47 times Volume 19, Issue 2 (April June)

7 GREKUL ET AL.: CANADA THISTLE AND FORAGE RESPONSES TO WIPING Tble 5. Non Cnd thistle plnt biomss in response to glyphoste wiping tretment t four psture sites in centrl Albert from 2000 nd 2001 (glyphoste experiment). Tretment Grss biomss 2000 Totl forb biomss b 2001 Grss biomss Annul forb biomss b biomss b Perennil forb kg/h P 0.01 P 0.01 P 0.58 P 0.06 P 0.96 Check 2, b 2, Glyphoste 2,131 b 1,519 2, Mens clculted for untrnsformed dt. Where pplicble, Tukey s test ws used for comprisons between tretments. Mens within column followed by different letters differ significntly (P 0.05). b P vlues nd men comprisons of forb biomss dt (nnul nd perennil) re bsed on squre root trnsformed dt. the nnul forb biomss of check plots during 2001 (Tble 6). In ddition, wiping with glyphoste resulted in the most perennil forb biomss the yer fter tretment (Tble 6), nd lthough it did not differ from the nontreted check, this tretment ws significntly greter (P 0.05) thn the piclorm plus 2,4-D tretment. Visully estimted legume cover did not differ between nontreted nd glyphoste-wiped plots but both were significntly (P 0.05) greter thn the other three herbicide tretments (Tble 6). At the time of wiping with glyphoste in both experiments, grss plnts t ll sites hd grown intermixed with Cnd thistle such tht it ws impossible to void incidentl contct of the wiper sponge with grss plnts, leding to some grss mortlity. Krueger-Mngold et l. (2002) found tht wheres wick-pplied glyphoste for Cnd thistle control in spring did not lter grss biomss, summer nd fll pplictions decresed grss biomss compred with the nontreted check. The systemic nture of glyphoste likely contributed to the grss dmge observed in both our experiments. Trnslocted glyphoste visibly killed not only the contcted grss stem, but interconnected surrounding shoots s well. This response ws pprent in 2000 s loclized ded ptches of grss, 10 to 50 cm in size, which were typiclly ssocited with dense Cnd thistle ptches tht hrbored tller grss stems t the time of wiping. In the second growing seson fter wiping, grsses hd begun to recover, s reflected in the nonsignificnt differences in grss biomss between wiped nd check plots in tht yer. Decreses in grss production ssocited with glyphoste tretment coincided with mrked increse in forb production. In both experiments, the increse in forb production ws result of the ppernce of nnul, weedy species. The mechnism responsible for the increse in nnul weeds is likely competitive relese (Begon et l. 1990). Vegettion succession in pstures fter disturbnces from burrowing nimls, livestock, nd mchines hs been linked to the competitive relese of species from vible seeds in the soil seed bnk (Begon et l. 1990; Trcy nd Snderson 2000; Willms nd Quinton 1995). In this study, reductions in Cnd thistle density nd biomss nd dmge to grsses cused by glyphoste resulted in ptches of bre ground tht were likely fvorble for the germintion nd estblishment of opportunistic, weedy, nnul forb species from the soil seed bnk or those rriving from djcent cultivted fields. Seedlings of Cnd thistle were generlly not evident in these res, reflecting the limited recruitment Tble 6. Non Cnd thistle plnt biomss in response to herbicide wiping tretments t three psture sites in centrl Albert during 2001 nd 2002 (multiple herbicide experiment). Wiping tretment Grss biomss Annul forb biomss 2001 Perennil forb biomss Visully estimted legume cover 2002 Totl herbge biomss kg/h % kg/h P 0.05 P 0.02 P 0.03 P P 0.79 Check 2, b 142 b 13 2,250 Glyphoste 1,818 b 1, ,118 2,4-D mecoprop dicmb 3, b 188 b 6 b 2,120 Clopyrlid 3,351 1 b 178 b 5 b 2,075 Piclorm 2,4-D 3, b 45 b 3 b 2,315 Mens clculted for untrnsformed dt. Where pplicble, Tukey s test ws used to compre tretments. Mens within column followed by different letters differ significntly (P 0.05). 304 Volume 19, Issue 2 (April June) 2005

8 WEED TECHNOLOGY of this species from seed (Donld 1990). In both experiments, nnul forb biomss in glyphoste-wiped plots begn to decline with time nd grsses incresed, suggesting return to more fvorble psture composition. Perennil forbs smpled in 2001 consisted lmost exclusively of dndelion, long with lsike nd white clover. The bundnt clover cover in plots wiped with glyphoste ws lrgely becuse of white clover, which ws present t high densities in 2001 nd White clover is n importnt psture legume in mny temperte countries nd is widespred cross Cnd (Turkington nd Burdon 1983). The reduction in vegettion nd bre ground in plots wiped with glyphoste likely creted conditions (i.e., reduced competition nd incresed light nd temperture) fvorble not only for the germintion nd growth of nnul, weedy forbs, but white clover s well. In this study, legumes (clover) were reduced by 2,4- D plus mecoprop plus dicmb, clopyrlid, s well s piclorm plus 2,4-D, 1 yr fter tretment (2001). These reductions re consistent with those of Boerboom nd Wyse (1988), who found glyphoste pplied with wiper resulted in less injury to birdsfoot trefoil thn dicmb, clopyrlid or piclorm. These uthors lso found tht piclorm pplied with wiper reduced birdsfoot trefoil. The results of this study, therefore indicte glyphoste my not injure clover to the extent of 2,4-D plus mecoprop plus dicmb, clopyrlid, or piclorm plus 2,4-D. Resons for this re likely becuse of the rpid binding of glyphoste to soil prticles upon contct compred with clopyrlid or piclorm nd my ccount for the loss of legume from wiped plots in the ltter two tretments. Implictions for Psture Mngement. Weed-wipers pper to provide n effective tool for perennil weed control in permnent pstures. Advntges of wiping compred with sprying include environmentl benefits such s decresed herbicide drift nd dmge to nontrget species, s well s economic benefits such s reduced dmge to legumes. However, wiping my or my not result in lower costs on per re bsis reltive to brodcst sprying given tht the mount of herbicide used is proportionl to the re nd mount (i.e., density) of weeds treted. Glyphoste t 33% concentrtion, sponge wiper pplied t either the lte-bud or seed-dispersl stge, provided control of Cnd thistle for up to 2 yr fter ppliction. However, even with hevy grzing to chieve height seprtion between forge nd Cnd thistle, glyphoste pplied with sponge wiper reduced grss production for up to 1 yr fter tretment, which in turn, led to the invsion of nnul weeds. Although glyphoste my not ffect shorter legumes, the benefits of Cnd thistle suppression my be outweighed by the reduction in grss production nd subsequent increse in nnul weeds. Among brodlef herbicides, the gretest reduction in Cnd thistle ws chieved for 2 yr through one-time ppliction with clopyrlid or piclorm plus 2,4-D, t v/ v concentrtions of 2 nd 20% (7 g i/l nd 13 plus 48 g i/l, respectively). Although 2,4-D plus mecoprop plus dicmb, clopyrlid, nd piclorm plus 2,4-D did not eliminte legume cover, they did reduce this component. The ppliction of clopyrlid, piclorm plus 2,4-D, or 2,4-D plus mecoprop plus dicmb with wiper hd the dded benefit of mintining grss production nd minimizing weed increses, which suggests these herbicides my provide vible lterntive to brodcst sprying or wiping with glyphoste for Cnd thistle control in pstures, prticulrly those contining few legumes. ACKNOWLEDGMENTS This reserch ws supported by the Albert Agriculture Reserch Institute (FFF Grnt ), together with contributions from Dow AgroSciences, BASF Cnd, nd McEwens Fuel nd Fertilizers. Additionl support ws provided by counties nd municipl districts cross centrl Albert. We thnk Alln Mculy nd severl lndowners for their coopertion in this project, s well s numerous summer field ssistnts for dt collection, prticulrly Crig Crr nd Sue Schttle. Finlly, we thnk Lind Hll nd two nonymous reviewers for their helpful comments on n erlier drft of the mnuscript. LITERATURE CITED Albert Agriculture Albert Forge Mnul. Agdex 120/20-4. Edmonton, AB, Cnd: Print Medi Brnch, Albert Agriculture, Food, nd Rurl Development. Alex, J. F Survey of weeds of cultivted lnd in the pririe provinces. Regin, Cnd: Experimentl Frm, Reserch Brnch, Cnd Agriculture. 68 p. Amor, R. L. nd R. V. Hrris Control of Cirsium rvense (L.) Scop. by herbicides nd mowing. Weed Res. 17: Begon, M., J. L. Hrper, nd C. R. Townsend Ecology: Individuls, Popultions nd Communities. 2nd ed. Cmbridge, MA: Blckwell Scientific. 945 p. Boerboom, C. M. nd D. L. Wyse Selective ppliction of herbicides for Cnd thistle (Cirsium rvense) control in birdsfoot trefoil (Lotus cornicultus). Weed Technol. 2: Boerboom, C. M. nd D. L. Wyse. 1988b. Influence of glyphoste concentrtion on glyphoste bsorption nd trnsloction in Cnd thistle (Cirsium rvense). Weed Sci. 36: Bovey, R. W. nd R. E. Meyer Control of huische nd honey mesquite with crpeted roller herbicide pplictor. J. Rnge Mng. 42: Volume 19, Issue 2 (April June)

9 GREKUL ET AL.: CANADA THISTLE AND FORAGE RESPONSES TO WIPING Donld, W. W Mngement nd control of Cnd thistle (Cirsium rvense). Rev. Weed Sci. 5: Gibson, H. G., L. D. Gultney, H. A. Holt, nd G. W. Krutz Rollerwiper herbicide pplictor: control of right-of-wy hrdwood brush. J. Arboric. 10: Goodwin, M. S., I. N. Morrison, nd A. G. Thoms A weed survey of pedigreed lflf seed fields in Mnitob. Cn. J. Plnt Sci. 66: Hggr, R. J., A. K. Oswld, nd W. G. Richrdson A review of the impct nd control of creeping thistle (Cirsium rvense L.) in grsslnd. Crop Prot. 5: Herr, D. E., E. W. Stroube, nd D. A. Ry The movement nd persistence of piclorm in the soil. Weeds 14: Hickmn, M. V., C. G. Messersmith, nd R. G. Lym Piclorm relese from lefy spurge (Euphorbi esul) roots in the field. Weed Sci. 37: Krueger-Mngold, J., R. L. Sheley, nd B. D. Roos Mintining plnt community diversity in wterfowl production re by controlling Cnd thistle (Cirsium rvense) using glyphoste. Weed Technol. 16: Myeux, H. S., Jr Appliction of herbicides on rngelnds with crpeted roller: shrub density influences volume, dosge, nd rte. Weed Sci. 35: Myeux, H. S., Jr. nd R. A. Crne Appliction of herbicides on rngelnds with crpeted roller: control of goldenweeds (Isocom spp.) nd flse broomweed (Ericmeri ustrotexn). Weed Sci. 32: Messersmith, C. G. nd R. G. Lym Roller ppliction of piclorm for lefy spurge control in pstures. Weed Sci. 33: Moomw, R. S. nd A. R. Mrtin Ropewick ppliction of piclorm for lefy spurge (Euphorbi esul) control. Weed Technol. 4: Moore, R. J The biology of Cndin weeds. 13. Cirsium rvense (L.) scop. Cn. J. Plnt Sci. 55: O Sullivn, P. A. nd V. C. Kosstz Absorption nd trnsloction of 14 C-3,6-dichloropicolinic cid in Cirsium rvense (L.) Scop. Weed Res. 24: Peterson, S. C. nd J. V. Prochetti Cnd thistle (Cirsium rvense) control in timothy (Phleum prtense) nd red clover (Trifolium prtense) swrd. Weed Sci. 26: [SAS] Sttisticl Anlysis Systems SAS/STAT User s Guide, Relese 6.03 edition. Cry, NC: Sttisticl Anlysis Systems Institute p. Shrm, M. P., F. Y. Chng, nd W. H. Vnden Born Penetrtion nd trnsloction of piclorm in Cnd thistle. Weed Sci. 19: Skinner, K., L. Smith, nd P. Rice Using noxious weed lists to prioritize trgets for developing weed mngement strtegies. Weed Sci. 48: Steel, R. G., J. H. Torrie, nd D. A. Dickey Principles nd Procedures of Sttistics: Biometricl Approch. New York: McGrw-Hill. 666 p. Thoms, A. G., B. L. Frick, nd L. M. Hll Albert Weed Survey of Cerel nd Oilseed Crops in Ssktoon, SK, Cnd: Agriculture Cnd, Weed Survey Series Publ p. Thoms, A. G. nd R. F. Wise Pece River Region of British Columbi Weed Survey of Forge Crops 1978, 1979 nd Regin, SK, Cnd: Agriculture Cnd, Weed Survey Series Publ pp. Trcy, B. F. nd M. A. Snderson Seedbnk diversity in grzing lnds of the Northest United Sttes. J. Rnge Mng. 53: Turkington, R. nd J. J. Burdon The biology of Cndin weeds. 57. Trifolium repens L. Cn. J. Plnt Sci. 63: Turnbull, G. C. nd G. R. Stephenson Trnsloction of clopyrlid nd 2,4-D in Cnd thistle (Cirsium rvense). Weed Sci. 33: Vnden Born, W. H Piclorm residues nd crop production. Cn. J. Plnt Sci. 49: Welker, W. V. nd D. L. Peterson A surfce-roller herbicide pplictor for weed control in turf. Weed Technol. 3: Willms, W. D. nd D. A. Quinton Grzing effects on germinble seeds on the fescue pririe. J. Rnge Mng. 48: Wyse, D. L. nd C. Hbstritt A roller herbicide pplictor. Proc. N. Cent. Weed Control Conf. 32: Volume 19, Issue 2 (April June) 2005