SNA Research Conference Vol Weed Control Mengmeng Gu Section Editor and Moderator Weed Control Section

Transcription

1 SNA Reserch Conference Vol Weed Control Mengmeng Gu Section Editor nd Modertor Weed Control Section 559

2 SNA Reserch Conference Vol Evlution of Pendimethlin + Dimethenmid-P for Reltive Sfety nd Efficcy Compred to Four Commercil Grnulr Herbicides Robert H. Stmps nd Annette L. Chndler University of Florid, Institute of Food nd Agriculturl Sciences, Dept. of Environmentl Horticulture, MidFlorid Reserch nd Eduction Center, Apopk, FL rstmps@ufl.edu Index words: crpe myrtle, lilyturf, plumbgo, spotted spurge, lrge crbgrss, eclipt, flse disy, rgweed prthenium, prthenium weed, Snt Mri feverfew, whitetop,, BrodStr, FreeHnd, Pendulum, OH2, Snpshot Significnce to Industry: Dimethenmid-P + pendimethlin () ws very effective in controlling spotted spurge, lrge crbgrss nd eclipt, nd lso effective t the higher tested rtes in controlling prthenium weed, n incresingly problemtic glyphoste (Roundup ) tolernt weed. Control of both spotted spurge nd prthenium weed using ws better thn the equivlent rte of pendimethlin pplied lone (Pendulum), indicting tht the dimethenmid-p in ws providing significnt control of these weeds. Dimethenmid-P hs different mode of ction thn the most commonly used preemergence nursery herbicides nd, therefore, could be used s n id to reduce the development of weed herbicide resistnce. In ddition, the combintion of dimethenmid-p + pendimethlin ws sfe, t wht will likely be lbeled use rtes, on the three ornmentl crops on which it ws tested. Nture of Work: Weed control in nurseries is continuing problem. This is prtly becuse the selection of preemergence herbicides lbeled nd sfe to use on ornmentls is limited, especilly s reltes to vilble modes of ction. A smll number of preemergence herbicides re typiclly used repetedly, cusing shifts in weed popultions towrd weeds tht those herbicides do not control well (tolernt weeds). In ddition, this prctice cn led to selection for herbicide resistnce. Also, new weeds re introduced into the industry on regulr bsis from contminted seed, liners nd plnts, s well s other sources. Therefore, when new ctive ingredient becomes vilble for triling, it is importnt to test its efficcy ginst both hrd to control nd new weeds. Phytotoxicity testing is lso importnt since it helps the herbicide compnies determine whether their products hve fit in the ornmentl industry. (BASF Corp., Reserch Tringle Prk, NC) is n experimentl grnulr herbicide contining 1% pendimethlin % dimethenmid-p ( group 15 herbicide). will be mrketed s FreeHnd. Prthenium weed (Prthenium hysterophorus L.), perhps the most troublesome nd noxious weed in both urbn nd rurl Indi (2) nd weed of ntionl significnce in Austrli (1), hs been detected in lmost hlf of the sttes in the U.S. (4). This ggressive weed is llelopthic, cn displce ntive plnts nd reduce biodiversity, is poisonous nd cn tint met nd milk of nimls tht et it, nd cuses llergic rections in nimls including humns (3). Eclipt [Eclipt prostrt (L.) L.] nd spurge (Chmesyce spp.) re frequently listed s some of the toughest weeds to control in nurseries (Society of Americn Florists, unpublished). Weed Control Section 560

3 SNA Reserch Conference Vol On 28 My 2007, 1½"-cell liners of crpe myrtle (Lgerstroemi indic Ptriot ), lilyturf (Liriope gignte Merton Jcobs ) nd plumbgo (Plumbgo uricult Imperil Blue ) were trnsplnted into 6½" nursery continers. Pots were filled with potting mix composed of pine brk: pet :snd (6:4:1 by vol) mended with 5 lbs/yd 3 of dolomite nd 0.5 lbs/yd 3 of micronutrient plus mgnesium supplement (STEP Hi-Mg, Scotts, Mrysville, OH). The pet component ws composed of equl prts composted municipl yrd wste, composted hrdwood brk nd Florid sedge pet. There were two continers of ech crop in ech plot nd the pots were plced on blck polypropylene ground cloth in full sun nd wtered using overhed irrigtion. Initil plnt height (ht), width t widest point (wd1), nd the perpendiculr width (wd2) mesurements were mde on 30 My. Additionl pots contining the sme growing medium were used to evlute tretment efficcy for controlling one grss [lrge crbgrss, Digitri snguinlis (L.) Scop.] nd three brodlef weeds [eclipt; spotted spurge, Chmesyce mcult (L.) Smll; prthenium weed]. Weed seeds were sown into pots on 31 My. Ech plot hd two pots of ech of the four weed species, ech pot sown with 20 seeds. Fourteen continers (two for ech of the three crops nd two for ech of the four weeds) were plced in ech 3' by 4' plot. Ech plot ws either left untreted (control) or ws treted with one of five herbicides 1.75 G (1% pendimethlin % dimethenmid-p) or BrodStr 0.25G (Vlent USA) or Pendulum 2G (BASF Corp.) or OH2 3G (The Scotts Co.) or Snpshot 2.5TG (Dow AgroSciences). ws pplied t three rtes (Tble 1). Herbicides were hnd brodcst under clm wind conditions on 1 June when ll plnt folige ws dry. After herbicide, ppliction the plots were irrigted with ½" of wter. Herbicides were repplied in the sme mnner on 27 July fter the weeds hd been hrvested nd the pots reseeded with nother 20 seeds ech. Tretments were replicted four times nd the design ws rndomized complete block. Periodiclly throughout the experiment, dt were collected regrding cute phytotoxicity (estimted visully s percentge from 0 100% where 0 = no injury nd 100 = plnt ded) nd chronic phytotoxicity (using differences in plnt growth s determined using plnt top growth indexes (PTGI) clculted using the formul PTGI = height ((wd1 + wd2) 2). Weed seedling counts were mde up to 28 dys fter the herbicide tretments were pplied nd successful germintion percentges were then clculted. Weed control percentges were bsed on differences between visul estimtes of weed coverge in herbicide-treted pots compred to the untreted control pots. The vlues for the two pots of ech weed in ech tretment nd repliction were verged prior to sttisticl nlysis. Prior to the second herbicide ppliction, the boveground prts of the weeds were cut from the continers, plced in pper bgs, dried t 131 F for 5 dys nd then weighed. Weed top dry weights were lso determined t experiment termintion. Dt were nlyzed by nlysis of vrince nd mens seprtions were by Duncn's new multiple rnge test t P 0.05 (SAS, SAS Institute, Cry, NC). Percent vlues were squre root or rcsin-squre-root trnsformed, s needed, prior to nlysis. Weed Control Section 561

4 SNA Reserch Conference Vol Results nd Discussion: Acute phytotoxicity. After the initil tretments, very minor phytotoxicity ws observed on crpe myrtle in the BrodStr (4 nd 7 dys fter initil tretment [DAIT]) nd OH2 (4 DAIT) plots. After the second tretment, only BrodStr cused visible dmge with low verge dmge rtings (0.8 to 6.7). By 77 dys fter the second tretments (DAST), no dmge ws visible in ny plot. Not surprising for lilyturf, the products contining group 14 herbicides (PPO inhibitors) cused significnt dmge. The dmge from BrodStr nd OH2 ws pprent 4 to 7 DAIT nd consisted of lef chlorosis occurring ner the bse of the leves. Dmge ws still visible t 77 DAST. The highest rte of cused minor dmge (verging 3.1 to 5.5) fter the second ppliction. Interestingly, the dmge did not pper until 42 DAST. None of the other tretments cused significnt phytotoxicity. As expected, plumbgo ws the most herbicide sensitive crop nd ws severely dmged by BrodStr. The medium rte nd OH2 tretments were modertely phytotoxic (verging 7.3 to 17.2), but the plnts hd grown out of the symptoms by the end of the tril. The high rte of ws somewht more dmging (verging 8.5 to 34.4) thn those tretments, but the plnts lso outgrew the injury by 77 DAST. Chronic phytotoxicity. Herbicide tretments hd no effect on chnges in plnt top growth indexes (PTGI) for crpe myrtle or liriope; however, growth of the sensitive indictor crop plumbgo ws reduced in the plots initilly treted with BrodStr nd the highest rte of. By 56 DAST, PTGI increses for plumbgo were not different from the control for ny of the tretments except BrodStr. Some of the plumbgo plnts were killed by the BrodStr tretment. The rte effect on plumbgo PTGI increse ws inversely liner. Weed Control germintion nd seedling survivl. At 28 DAIT, spotted spurge control rnged from 83 (Pendulum nd low ) to 100% (ll the other tretments). At 28 DAST, control ws 95% or higher for ll tretments. Control of lrge crbgrss ws 100% for ll tretments t ll dtes. Eclipt seed germintion ws very low but by 28 DAST ws enough for tretment comprison. Successful seedling survivl ws not reduced using OH2 nd ws reduced by 72 nd 81%, respectively, by Snpshot nd Pendulum. Control ws 100% with BrodStr nd ll rtes of. For prthenium weed t 28 DAIT, successful seedling estblishment ws reduced by ll tretments except the low nd middle rtes of. OH2 nd Snpshot provided 100% control. At 28 DAST, ll tretments except Pendulum provided very good to excellent (88 to 98%) prthenium control. Weed control coverge nd dry weights. Spotted spurge ws well controlled by ll herbicide tretments; however by 56 DAST, Pendulum ws less effective (bsed on coverge) thn the others with the exception of Snpshot (Tble 1). Lrge crbgrss control ws 100% for ll tretments. Eclipt ws not controlled by OH2 nd poorly suppressed by Snpshot but the other tretments provided control with BrodStr nd ll rtes of giving excellent control. Prthenium weed control ws rte relted for with only the highest rte providing significnt control fter the first sowing nd the middle nd high rtes providing good to excellent suppression fter the second ppliction. Pendulum ws not effective, indicting tht it ws the dimethenmid-p in tht ws controlling prthenium weed. Control t 56 DAIT/DAST rnged from 71.5 to 100% for BrodStr, OH2 nd Snpshot. Weed Control Section 562

5 SNA Reserch Conference Vol Acknowledgements: We thnk BASF Corportion nd the Florid Agriculturl Experiment Sttion for supporting this reserch. Tble 1. Weed control, bsed on visul estimtes of weed coverge of the medium surfce, nd weed dry weights. Applicti on rte (lb.i. /A) spotted spurge lrge crbgrss eclipt Weed control (%) prthenium weed DAIT z DAST y DAIT z DAST y DAIT z DAST y DAIT z DAST y Tretments Untreted control 0.0 b x 0.0 c 0.0 b 0.0 b w 0.0 b 0.0 c 0.0 c bc 61.3 b bc b b 95.0 BrodStr G b OH2 3G b 88.5 Pendulum b G bc 8.7 c Snpshot b 45.0 b 2.5G b Dry weed weight (g) DAIT z DAST y DAIT z DAST y DAIT z DAST y DAIT z DAST y Untreted 3.8 b x b control b 17.6 b b 5.1 c 19.5 b b 2.6 b b 2.6 b b BrodStr 0.25G b 0.0 OH2 3G c Pendulum G bc b 17.2 b Snpshot 2.5G bc z DAIT = dys fter initil herbicide tretments. y DAST = dys fter second herbicide tretments. x Mens seprtion within columns nd ctegory by Duncn s new multiple rnge test t P w There ws indequte eclipt seed germintion for sttisticl nlysis. Weed Control Section 563