Potential Impact of Submersed 2,4-D and Triclopyr Applications on Native Emergent Plants

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1 Potentil Impct of Submersed 2,4-D nd Triclopyr Applictions on Ntive Emergent Plnts by LeeAnn M. Glomski, Michel D. Netherlnd, nd Lind S. Nelson PURPOSE: The potentil for herbicide dispersion from treted sites cn cuse concerns regrding the impct on desirble floting-lef nd emergent vegettion. There re mny scenrios where trgeted submersed invsive weeds nd non-trget floting-lef nd emergent plnts grow in close proximity. This study ws conducted to determine the effects of submersed pplictions of the uxin-mimicking herbicides 2,4-D nd, on sptterdock (Nuphr lute (L.) Sm.), Americn bulrush (Schoenoplectus mericnus Pers.), nd soft-stem bulrush (S. tbernemontni (C.C. Gmel.) Pll). Use rtes nd exposures tht provide of the submersed invsive Eursin wtermilfoil (Myriophyllum spictum L.) were evluted ginst these vluble non-trget emergent species. BACKGROUND: Sptterdock nd bulrush species re ecologiclly importnt shoreline plnts in mny Midwestern lkes. They provide vluble hbitt for fish nd invertebrtes. The seeds re food source for wterfowl nd the rhizomes re eten by muskrts, bever, nd porcupines (Bormn et. l 1997). Sptterdock nd bulrush species re often found mixed with or in close proximity to the invsive submersed plnt Eursin wtermilfoil. Submersed pplictions of 2,4-D (both the ester nd mine formultions) nd re commonly used to Eursin wtermilfoil nd there is concern tht these pplictions my cuse unintended dmge to non-trget emergent nd flotingleved plnt stnds. Westerdhl nd Getsinger (1988) nd Thyer (1985) hve reported tht bulrush species re susceptible to folir pplictions of 2,4-D mine nd grnulr pplictions of, brodcst t the bse of the plnts. Moreover, rtes of tht bulrush species re susceptible to re similr to those used to Eursin wtermilfoil. Nonetheless, the impct of lower use rtes nd vrious exposure periods on bulrush species is uncertin. There is no published informtion on the impcts of on bulrush. Previous reserch conducted by Glomski nd Nelson (28) studied the effects of submersed pplictions of nd on sptterdock. Similr to Hnlon nd Hller (199, 1991), sptterdock showed initil injury symptoms such s lef nd petiole curling nd petiole elongtion. Six weeks fter tretment, however, only sptterdock treted t 1.5 nd 2.5 mg L -1 nd 2. mg L -1 hd significntly less biomss thn the untreted. The verge biomss reduction for these tretments ws 48 percent. Sptterdock treted with lower concentrtions of or (.25,.5, nd 1. mg L -1 ) for 24-hr exposure period were not significntly different thn untreted plnts. Although low rtes of both herbicides did not significntly reduce sptterdock biomss fter 24 hr of exposure, it is unknown if longer exposure (>24 hr) to low rtes of these herbicides will injure sptterdock. 1

2 MATERIALS AND METHODS: Two studies were conducted to determine the effects of submersed pplictions of 2,4-D nd on two bulrush species nd sptterdock. Study 1 Bulrush. To test the effects of rnge of nd concentrtions ginst Americn nd soft-stem bulrush, n outdoor mesocosm study ws conducted in the summer of 27 t the Center for Aqutic nd Invsive Plnts in Ginesville, FL. Americn nd soft-stem bulrush were grown from rhizomes purchsed from Suwnnee Lbs in Lkelnd, FL. Bulrush rhizomes (5 to 15 cm) were plnted in 3.78-L pots (1 rhizome/pot) filled with potting soil mended with Osmocote fertilizer ( ) t rte of 5 g kg -1 soil. Plnts were given 6-week pretretment growth period nd shoots were well estblished t the time of tretment. Three pots of ech bulrush species were plced into 95-L tnks filled with wter to depth of 42 to 45 cm. Tretments were pplied on August 9, 27, nd included:..25,.5, 1., 1.5, nd 2.5 mg L -1 s Aqukleen (27.6 % i, United Phosphorous Inc., King of Prussi, PA);.25,.5, 1., nd 2. mg L -1 mine s Renovte 3 (44.4 % i, SePRO Corportion, Crmel, IN); nd n untreted. Low rtes of both products (.25,.5 mg L -1 ) represented potentil rtes tht could be encountered vi drift from Eursin wtermilfoil-treted sites nd higher rtes represented those typiclly used to Eursin wtermilfoil. After 24-hr exposure to herbicide, ll tnks were drined nd refilled with untreted wter to remove queous herbicide residues. The exposure period nd herbicide use rtes for this study were similr to previous wter lily nd sptterdock studies conducted by Glomski nd Nelson (28). Visul evlutions were conducted on weekly bsis. Six weeks fter tretment (WAT), shoot nd root biomss were hrvested, dried to constnt weight t 65 C, nd dry weights were recorded. Study 2 Sptterdock. To test the effect of low rtes nd extended exposures of 2,4-D nd ginst sptterdock, n outdoor mesocosm study ws conducted in the summer of 27 t the U.S. Army Engineer Reserch nd Development Center, Lewisville Aqutic Ecosystem Reserch Fcility (LAERF) in Lewisville, TX. Sptterdock rhizomes (1 to 15 cm) were plnted into 3.78-L pots (one rhizome/pot) filled with LAERF pond sediment mended with 3 g L -1 Osmocote fertilizer (16:8:12) per pot. Plnt propgules were obtined from Kester s Wild Gme Food Nurseries Inc., Omro, WI. Four plnted pots were plced into 76-L tnks filled to depth of 5 cm with lumtreted Lke Lewisville wter. Plnts were llowed to grow for 5 weeks prior to tretment. Tretments were pplied on August 6, 28, nd included: (Aqukleen ) t.25 nd.5 mg L -1 ; 2,4-D mine (s DMA 4 IVM, 46.3 % i, Dow AgroSciences, Indinpolis, IN) t.25,.5 nd.75 mg L -1 ; (Renovte 3 ) t.25 or.5 mg L -1 ; nd n untreted. After four weeks of herbicide exposure, ll tnks were drined nd refilled with untreted wter. Six WAT, ll boveground nd belowground biomss ws hrvested, dried, nd weighed. For both studies, tretments were rndomly ssigned to tnks nd replicted four times. Dt were subjected to one-wy nlysis of vrince (ANOVA). Where tretment differences were detected, post-hoc test ws conducted using the Student-Newmn-Keuls method (α =.5). 2

3 RESULTS AND DISCUSSION: Study 1 Bulrush. Americn bulrush did not show severe injury symptoms throughout the herbicide tretment, nd by 6 WAT, neither shoot nor root biomss ws sttisticlly different thn the untreted (Figures 1A nd 1B). Compred to untreted plnts, soft-stem bulrush shoot biomss ws reduced by 46 to 61 percent t rtes of 1.5 nd 2. mg L -1 nd 1.5 nd 2.5 mg L -1 (Figure 2A). Lower rtes (< 1. mg L -1 ) of nd showed no impct on shoot growth. Visul observtions suggest the shoot tissue of soft-stem bulrush ws initilly impcted by the higher rte tretments of 2,4-D nd. The biomss mesured t the end of the study cme from new shoot tissue emerging from the rhizomes. Soft-stem bulrush root biomss ws lso significntly reduced t rtes >1. mg L -1 nd.5 mg L -1 (Figure 2B). While soft-stem bulrush shoots recovered from ll herbicide tretments by the time of hrvest, the initil severity of injury observed t the higher use rtes would suggest tht selectivity could be compromised t higher tretment rtes. Study 2 Sptterdock. One WAT, petiole elongtion nd curling nd slight lef curling (epinsty) were present on plnts treted with.5 mg L -1 nd higher for ll herbicides. By 3 WAT, the.25 mg L -1 tretments (ll herbicides) exhibited slight epinsty s well. The most severe symptoms were observed on plnts exposed to.75 mg L -1 2,4-D mine. Epinsty is n indictor of exposure to uxin-mimicking herbicides; however, these symptoms do not lwys trnslte to plnt. Similr to results reported by Glomski nd Nelson (28), initil injury symptoms did not trnslte to plnt in this study. Despite initil injury symptoms, none of the tretments reduced shoot or root biomss by 6 WAT (Figures 3A nd 3B). The results of these studies showed tht both nd rtes used to Eursin wtermilfoil could cuse substntil injury to soft-stem bulrush; however, Americn bulrush would likely not be ffected by the higher herbicide use rtes. In res where soft-stem bulrush nd Eursin wtermilfoil re intermixed, lowering the rte of by.5 to 1. mg L -1 could reduce the impct to soft-stem bulrush, but still provide good of Eursin wtermilfoil (Netherlnd nd Getsinger 1992). Lowering the rte of would lso reduce injury to softstem bulrush; however, longer exposure period would be necessry to chieve good of Eursin wtermilfoil (Elliston nd Stewrd 1972, Green nd Westerdhl 199). Recent reserch by Glomski nd Netherlnd (28) suggested tht rtes of.7 to.25 mg L -1 2,4-D mine nd.25 to.25 mg L -1 following extended (7 weeks) exposure provided nerly complete of Eursin wtermilfoil. The current study showed tht 4-week exposure to lower rtes of both 2,4-D mine nd (.25 nd.5 mg L -1 ) did not significntly impct sptterdock shoot or root biomss. Although the exposure periods differ between the current study nd tht of Glomski nd Netherlnd (28), the dt suggest tht low-dose tretments of 2,4-D mine or could selectively remove Eursin wtermilfoil where intermixed with sptterdock. 3

4 Shoot Biomss (g D.W.) A b b b b b b b b b b Root Biomss (g D.W.) B 2 Rte (mg L -1 ) Figure 1. Men (± SE) dry weight (D.W.) of Americn bulrush shoot (A) nd root (B) biomss collected 6 weeks fter 24-hr exposure to nd. Brs shring the sme letter do not significntly differ from ech other ccording to Student-Newmn-Keuls post-hoc test; α =.5. 4

5 1 8 A Shoot Biomss (g D.W.) b b c c b b b bc c Root Biomss (g D.W.) B bc bc bcde efg g b bcd cdef defg fg Rte (mg L -1 ) Figure 2. Men (± SE) dry weight (D.W.) of soft-stem bulrush shoot (A) nd root (B) biomss collected 6 weeks fter 24-hr exposure to nd. Brs shring the sme letter do not significntly differ from ech other ccording to Student-Newmn-Keuls post-hoc test; α =.5. 5

6 Shoot Biomss (g D.W.) A 2,4-D mine 12 1 B 2,4-D mine Root Biomss (g D.W.) Rte (mg L -1 ) Figure 3. Men (± SE) dry weight (D.W.) of sptterdock shoot (A) nd root (B) biomss collected 6 weeks fter 4-week exposure to, nd 2,4-D mine. There were no significnt differences mong the tretments ccording to Student-Newmn-Keuls post-hoc test; α =.5. 6

7 FUTURE WORK: Bsed on the difference in herbicide ctivity on Americn nd soft-stem bulrush, further reserch evluting the response of ntive qutic plnt species to specific herbicide tretment strtegies will be conducted. Field residue smpling confirms tht some lrge-scle tretments with 2,4-D nd cn result in ntive plnts receiving extended exposures to low rtes of these herbicides. While lb studies confirm tht low use rtes nd long exposures of 2,4-D nd re effective for ling Eursin wtermilfoil, more reserch is needed to further determine the selectivity implictions of this tretment strtegy. Due to the desire to protect ntive emergent wetlnd plnts in the northern United Sttes, future studies should focus on other ntive floting-lef nd emergent vegettion. ACKNOWLEDGMENTS: Support for this project ws provided by the Aqutic Plnt Control Reserch Progrm (APCRP). The uthors would like to thnk Hether Theel for her technicl ssistnce. Cittion of trde nmes does not constitute n officil endorsement or pprovl of the use of such products. POINTS OF CONTACT: For dditionl informtion, contct the uthors, LeeAnn M. Glomski (972) , LeeAnn.M.Glomski@usce.rmy.mil; Michel D. Netherlnd (352) , Michel.D.Netherlnd@usce.rmy.mil; or Lind S. Nelson (61) , Lind.S.Nelson@usce.rmy.mil or the Mnger of the Aqutic Plnt Control Reserch Progrm, Robert Gunkel (61) , Robert.C.Gunkel@usce.rmy.mil. This technicl note should be cited s follows: Glomski, L. M., M. D. Netherlnd, nd L. S. Nelson. 29. Evlution of 2,4-D nd ginst sptterdock nd bulrush. APCRP Technicl Notes Collection (ERDC/TN APCRP-CC-1). Vicksburg, MS: U.S. Army Engineer Reserch nd Development Center. REFERENCES Bormn, S., R. Korth, nd J. Temte Through the looking glss A field guide to qutic plnts. Merrill, WI. Elliston, R. A., nd K. K. Stewrd The response of Eursin wtermilfoil to vrious concentrtions nd exposure periods of 2,4-D. Hycinth Control J. 1:38-4. Glomski, L. M., nd L. S. Nelson. 28. Evlution of nd mine ginst wterlily nd sptterdock. APCRP Technicl Notes Collection (ERDC/TN APCRP-CC-7). Vicksburg, MS: U.S. Army Engineer Reserch nd Development Center. Glomski, L. M., nd M. D. Netherlnd. 28. Response of hybrid milfoil to low use rtes nd extended exposures of 2,4- D nd. In 48 th Annul Meeting of the Aqutic Plnt Mngement Society, Chrleston, SC, July 13-16, Green, W. R., nd H. E. Westerdhl Response of Eursin wtermilfoil to 2,4-D concentrtion nd exposure times. J. Aqut. Plnt Mnge. 28: Hnlon, C., nd B. Hller The impct of 2,4-D used in wter hycinth progrms on the growth of nontrget sptterdock. Aqutics 12(1): Hnlon, C., nd B. Hller The effect of 2,4-D mine on the growth of sptterdock. Aqutics 13(1):

8 Netherlnd, M. D., nd K. D. Getsinger Efficcy of on Eursin wtermilfoil:. Concentrtion nd exposure time effects. J. Aqut. Plnt Mnge. 3:1-5. Thyer, D. D Evlution of techniques for improving the efficcy of herbicides. Qurterly report USDA/SEA/ARE. Ginesville, FL: University of Florid. Westerdhl, H. E., nd K. D. Getsinger Aqutic plnt identifiction nd herbicide use guide; Volume II:. Aqutic plnts nd susceptibility to herbicides. Technicl Report A Vicksburg, MS: U.S. Army Engineer Wterwys Experiment Sttion. NOTE: The contents of this technicl note re not to be used for dvertising, publiction, or promotionl purposes. Cittion of trde nmes does not constitute n officil endorsement or pprovl of the use of such products. 8