The Impact of Planting Date on Management of the Rice Water Weevil in Louisiana Rice

Transcription

1 The Open Entomology Journl, 211, 5, Open Aess The Impt of Plnting Dte on Mngement of the Rie Wter Weevil in Louisin Rie M.J. Stout*,1, N.A. Hummel 1, M.J. Frey 2 nd W.C. Rie 3 1 Deprtment of Entomology, Louisin Stte University Agriulturl Center, Bton Rouge, LA, 783, USA 2 Rie Reserh Sttion, Louisin Stte University Agriulturl Center, Crowley, LA, USA 3 USDA, ARS, CPRL, Bushlnd, TX 7912, USA Astrt: The rie wter weevil, Lissorhoptrus oryzophilus, is the most destrutive inset pest of rie in the United Sttes. Erly plnting of rie to void dmging infesttions of the rie wter weevil hs long een suggested s mngement tti. A five-yer study ws onduted to hrterize the influene of rie plnting dte on rie wter weevil mngement in light of reent trends towrd erlier plnting of rie in Louisin. Experimentl designs differed mong yers: experiments in 21 nd 28 were split-plot studies, wheres in 23, 24, nd 27, seprte rndomized lok experiments were onduted. Results from these experiments showed tht erly plnting of rie filitted rie wter weevil mngement in three wys. Weevil infesttions were lighter in rie plnted in mid- to lte Mrh thn in lter-plnted rie in three of five yers of the study. In ddition, yield losses ttriutle to weevil feeding were lower in erly plnted rie thn in lte plnted rie in the two split-plot experiments. Finlly, single pplitions of lmd-yhlothrin ( pyrethroid pplied to rie fter flooding to kill weevil dults) were less effetive in lte plnted rie thn in erly plnted rie. This study demonstrtes tht erly plnting n serve s n importnt omponent of mngement progrm for rie wter weevils in Louisin. Keywords: Rie, Oryz stiv, rie wter weevil, Lissorhoptrus oryzophilus, integrted pest mngement, plnting dte, erly plnting, insetiides. INTRODUCTION The rie wter weevil (RWW), Lissorhoptrus oryzophilus Kushel, is the most widely distriuted nd destrutive erlyseson inset pest of rie, Oryz stiv L., in the United Sttes [1]. It hs reently invded importnt rie-produing regions of Asi nd Europe [2] nd thus poses glol thret to rie prodution. The sesonl history of this inset egins in erly spring, when dult RWWs emerge from overwintering sites, whih inlude lef litter, unh grsses, nd stule in nd round rie fields, nd fly to rie fields [3]. Adult weevils feed on the leves of rie, ut this form of injury is not eonomilly importnt exept under unusully hevy infesttions. Femles oviposit primrily in lef sheths eneth the wter surfe [4]. Infesttions of lrve thus ommene when stnding wter is present in rie field, ondition met fter fields re flooded. Lrve my feed in or on leves for short period of time, ut quikly move down to the roots, where they feed on or in the roots of rie. The insets pss through four instrs nd pupl stge on roots in pproximtely 3 dys [5]. Although popultions of the weevil re multivoltine, only single pek of lrvl undne is usully oserved in rie field [3]. Feeding y lrve on the roots of rie plnts results in redued tillering nd shoot growth in the vegettive phses of development, nd redued pnile densities nd grin weights t hrvest [6]. *Address orrespondene to this uthor t the Deprtment of Entomology, 44 Life Sienes Building, Louisin Stte University, Bton Rouge, Louisin, 783, USA; Tel: (225) ; Fx: ; E-mil: mstout@gtr.lsu.edu Yield losses ttriutle to injury y this inset n exeed 2% [6]. The most ommonly used tti for mnging L. oryzophilus is the pplition of insetiides. Prior to 1998, RWWs were mnged with post-flood pplitions of rofurn to eliminte lrve feeding on roots. Following the disllowne y the EPA of rofurn in rie, severl pyrethroids nd seed tretment of fipronil were registered for RWW ontrol, trgeting, respetively, the dult stge nd lrvl stges of the inset [7]. The fipronil seed tretment ws voluntrily removed from the mrket in 24. Reently, newer seed tretments hve een introdued for RWW ontrol, inluding thimethoxm nd hlorntrniliprole seed tretments. All of the urrently registered insetiides, espeilly the seed tretments, provide dequte protetion ginst the RWW in most irumstnes [7-9]. There my e, however, serious prolems with the use of insetiides in rie, most notly negtive effets on non-trget invertertes. Alterntive ttis ginst the RWW re therefore needed. Erly plnting hs long een suggested s mngement tti ginst the RWW [,11]. The sis for this suggestion is potentil synhrony etween rie plnting, whih egins in Mrh in southwest Louisin, nd the emergene of weevils from overwintering sites. Emergene of dults from overwintering hitts in spring is influened y temperture, eginning in lte Mrh to erly April in southern rie-growing regions of the United Sttes [5] nd lter in more northern rie-growing regions [12]. This emergene is / Benthm Open

2 2 The Open Entomology Journl, 211, Volume 5 Stout et l. protrted proess tht my our over the ourse of two or more months [3,13]. The nture nd timing of RWW emergene suggests tht erly plnting of rie my e mens of voiding dmging weevil infesttions. This ulturl prtie hs een evluted previously, with mixed results (e.g., [14,15]). However, in reent yers, reommended plnting dtes hve een moved forwrd in Louisin nd elsewhere [16], nd there is need to re-evlute this tti in light of these revised reommendtions. The series of experiments desried here ws onduted to evlute the impt of plnting dte on RWW undne, rie yields nd yield losses, nd insetiide effiy in smll rie plots. MATERIALS AND METHODS Generl Experiments were onduted in 21, 23, 24, 27, nd 28 t the Louisin Stte University Agriulturl Center Rie Reserh Sttion loted ner Crowley, Adi Prish, Louisin. Experimentl designs vried somewht mong yers (Tle 1); however, in ll five yers, grin yields nd densities of RWW lrve nd pupe were ompred in insetiide-treted nd untreted rie sown on two to four dtes representing, t minimum, erly nd mid or lte plnting dtes. Erly, mid, nd lte plnting dtes were hosen with referene to the reommended rnge of optimum plnting dtes for southwest Louisin, Mrh 15 to April 2 [16], with erly plnting ourring in mid to lte Mrh, mid plnting ourring in mid April, nd lte plnting ourring in lte April to erly My. The effet of plnting dte on the severity of weevil infesttions ws evluted y estimting densities of RWW lrve nd pupe in rie plnted on different dtes. In ddition, the inlusion of insetiide-treted plots in ll experiments llowed yield losses to e ompred mong plnting dtes nd lso llowed investigtion of the hypothesis tht the effiies of insetiide tretments vried with plnting dte. Fields used in these experiments hve een in rie-fllow rottion for over 2 yers nd the soil type in ll fields ws Tle 1. Experimentl Designs nd Dtes of Plnting, Flooding, nd Inset Smpling for Plnting Dte Experiments Conduted from 21 to 28, LSU AgCenter Rie Reserh Sttion, Crowley, Louisin Yer Crowley silt lom (fine smetiti, thermi, Typi Alqulf). Agronomi prties used in ll experiments were, unless otherwise noted, those reommended y the LSU AgCenter for southwest Louisin [16]. Generlly, fertilizer ws pplied t reommended rtes s pre-plnt rodst pplition of N-P-K fertilizer ( ) nd n dditionl rodst pplition of N s ure (46% N) mde just prior to flood estlishment. Densities of L.oryzophilus lrve nd pupe were estimted y removing two to four root/soil ore smples from the interior of plots [5]. Core smpling ws onduted one or twie for ll experiments etween three nd five weeks fter permnent flood. The ore smpler ws metl ylinder with dimeter of 9.2 m nd depth of 7.6 m tthed to metl hndle. Root/soil ores were pled into 4 mesh sreen sieve ukets nd soil nd insets were wshed from roots under pressure. Bukets were pled into sins with sturted slt wter, nd lrve nd pupe were ounted s they floted to the wter surfe. Rie ws hrvested using smll plot omine when rie grin rehed moisture ontent of 17 to 2 mg g -1. Rough rie grin yields were djusted to stndrd moisture ontent of 12 mg g -1. Split-Plot Experiments: 21 nd 28 Experiments onduted in 21 nd 28 were split-plot experiments, with plnting dte s the min-plot ftor nd insetiide tretment s the su-plot ftor. Replition of the plnting dte ftor in min plots in this experimentl design llowed the effets of plnting dte on densities of RWW lrve nd pupe nd on yields to e sttistilly nlyzed. 21 experiment: The min plot ftor (plnting dte: erly, mid, nd lte) ws rrnged s rndomized omplete lok with three replitions. Min plots were seprted y erthen levees nd eh min plot hd seprte ess to lterl for irrigtion. The suplot ftor ws insetiide tretment (untreted or treted with the insetiidl seed tretment fipronil (Ion 6.2 FS Byer Crop Siene]) nd suplots were rrnged rndomly within min plots, with Experimentl Design Erly Plnting Dte Mid Plnting Dte(s) Lte Plnting Dte Plnt Flood Core smples Plnt Flood Core smples Plnt Flood Core smples 21 Split-plot 27 Mrh 18 April 9, 21 My 9 April 3 April 21 My, 4 June 3 April 22 My 12, 26 June 23 Seprte RCB experiments 25 Mrh 1 My 28 My 16 April 15 My 9 June 8 My 5 June 1 July 24 (wterseeded) Seprte RCB experiments 15 Mrh 14 April 13 My 1 April, 14 April 3 April, 12 My 26 My, 8 June 3 April 24 My 22 June 27 Seprte RCB experiments 8 Mrh 11 April 7, 17 My 17 April My 5, 14 June Split-plot 24 Mrh 24 April 2, 29 My My 28 My 24 June, 1 July

3 Plnting Dte nd Rie Wter Weevils in Louisin The Open Entomology Journl, 211, Volume 5 3 three suplots of eh tretment in eh min plot. Thus, for eh plnting dte, there were totl of 18 suplots, nine eh of two insetiide tretments distriuted over three min plots. Erly-, mid-, nd lte plnted plots were sown on 27 Mr, 9 Apr, nd 3 Apr, respetively. All suplots were drillseeded to depth of 2 m with the rie ultivr Cypress, semi-dwrf long-grin, t seeding rte of 1.25kg of seed per hetre. Suplots mesured 1.25 m (7 rows t 17.8 m row sping) y 7.6m. For seeds ssigned to the insetiide tretment, Ion 6.2 FS ws pplied y hnd shortly efore sowing t rte equivlent to.56kg i per hetre. Flood ws estlished on 18 Apr, 3 Apr, nd 22 My for erly-, mid-, nd lte plnted plots, respetively. Plnts possessed three to four fully-expnded leves when flooded. Core smples were tken to estimte densities of weevils on two dtes for eh min plot. For erly plnted rie, ore smples were tken on 9 My nd 21 My (21 nd 33 df, respetively); for the mid-plnting dte, smples were tken on 21 My nd 4 Jun (21 nd 35 df, respetively); for the lte plnting dte, smples were tken on 12 nd 26 Jun (21 nd 35 df, respetively. Erly-, mid-, nd lte plnted plots were hrvested on 6 Aug, 6 Aug, nd 9 Sept, respetively). 28 experiment: In this experiment, min plots (erly vs. lte plnting dtes) were rrnged s rndomized omplete lok with three replitions. The suplot ftor ws insetiide tretment (four tretments) with tretments rrnged s rndomized omplete lok within min plots with two replitions per min plot. Thus, for eh plnting dte, there were totl of six suplots of eh insetiide tretment. The four insetiide tretments inluded n untreted ontrol, n insetiidl seed tretment of Dermor X- (Rynxypyr [hlorntrniliprole], DuPont Crop Protetion), single post-flood pplition of Krte Z (lmd-yhlothrin, Syngent Crop Protetion), nd two post-flood pplitions of Krte Z. Erly-plnted plots were drill-seeded with the vriety Coodrie s desried for the 21 experiment on 24 Mr, while lte plnted plots were drill-seeded on 2 My. Suplot size in this experiment ws 1.25m (7 rows t 17.8m row sping) y 5.5m, nd suplots were surrounded y metl flshing to redue movement of insetiides in wter from suplot to suplot. Seeds ssigned to the Dermor tretment were treted y hnd with Dermor X- t rte of.3 mg i per seed. Suplots ssigned to oth of the lmdyhlothrin tretments were spryed with lmdyhlothrin with kpk, CO 2 -powered spryer t rte of.34kg i per hetre few hours fter flooding, nd the seond pplition of lmd-yhlothrin ws mde to pproprite suplots seven df (lte plnted suplots) or eight df (erly plnted suplots). Permnent flood ws pplied to erly plnted min plots on 24 Apr, nd to lte plnted min plots on 28 My. Core smples were tken to estimte densities of weevils on two dtes for eh min plot. For erly plnted rie, ore smples were tken on 2 nd 29 My (26 nd 35 df); for the lte plnting dte, smples were tken on 24 Jun nd 1 Jul (26 nd 33 df, respetively). Erly nd lte plnted plots were hrvested on 7 nd 19 Aug, respetively (yields were not tken from severl plots due to poor stnd estlishment). Rndomized Complete Blok Experiments: 23, 24, nd 27 Studies In ddition to the split-plot experiments desried ove, dditionl studies were onduted in 23, 24, nd 27. Studies in eh of these yers onsisted of seprte rndomized lok experiments plnted on two or more dtes. Eh experiment ws onduted in seprte leveed re with ess to lterl for irrigtion. Within eh experiment, plots treted or not treted with insetiides were rrnged s rndomized omplete loks with four to five replitions. Densities of weevil lrve nd pupe in plots were determined one or twie, etween three nd five weeks fter flooding. Yields from plots were lso determined t the end of the seson. This design llowed the effets of insetiide tretment on weevil densities nd yields to e nlyzed sttistilly for eh plnting dte seprtely, ut did not llow sttistil omprisons of weevil densities mong plnting dtes. Nonetheless, qulittive ssessment of the effet of plnting dte on weevil densities ws possile, euse experimentl designs, smpling proedures, nd gronomi prties used for eh experiment were similr. 23 study: Seprte experiments were drill-seeded (v. Coodrie ) on 25 Mr, 16 Apr, nd 8 My. Eh of these experiments ws rndomized omplete lok experiment with two tretments (insetiide-treted nd ontrol) nd four replites. Insetiide tretment onsisted of fipronil seed tretment t rte of.675 kg i per hetre. The plot size in this experiment ws 1.25m y 5.8m (7 rows t 17.8m drill sping) nd the seeding rte ws 1 kg h -1. Permnent floods were pplied on 1 My, 15 My, 5 Jun for the erly, mid, nd lte plnting dtes, respetively. Three ore smples were tken from plots to estimte densities of weevil lrve nd pupe 27, 25, nd 26 df for the erly, mid, nd lte plnting dtes, respetively. Entire plots were hrvested on 28 Jul, 14 Aug, nd 8 Sept. 24 study: In 24, plots were wter-seeded rther thn drill-seeded s in other yers. In other respets, however, this study ws similr to the one onduted in 23. The experimentl design for experiments ws rndomized lok with two tretments (ontrol nd insetiide-treted) nd five replitions. Plots were seeded on 15 Mr, 1 Apr, 14 Apr, nd 3 Apr. For wter-seeding, pre-weighed liquots of seeds (ultivr Coodrie ) were soked in wter for 24 hr to indue germintion. After removing seeds from sok wter, seeds ssigned to the insetiide tretment were treted with fipronil t rte equivlent to.8kg i per hetre. Seeds were then st into flooded, premesured 1.2m x 6.1m plots. Seeding rte ws 157.5kg seed per hetre. Plots were drined within 48 hr of seeding to llow plnts to estlish. Permnent floods were estlished on 14 Apr, 3 Apr, 12 My, nd 24 My. Plnts possessed three to four fully expnded leves t flooding. Beuse there were onerns out the effiy of fipronil in wter-seeded ulturl system, rofurn grnules (Furdn 3G FMC Corportion) were pplied to plots ssigned to insetiide tretments 17 to 19 df to further ontrol weevils in these plots. Three ore smples were tken from eh plot for eh plnting dte 27 to 29 df to estimte densities of weevil lrve nd pupe. Plots were hrvested on 19 Jul, 29 Jul, 11 Aug, nd 16 Aug. 27 study: In 27, seprte experiments were drillseeded on 8 Mr (erly plnting) nd 17 Apr (mid plnting)

4 4 The Open Entomology Journl, 211, Volume 5 Stout et l. using the vriety Coodrie t 1.25 kg seed per hetre (wet wether onditions prevented lte plnting in 27, lthough omprle experiment ws wter-seeded on 16 My). These drill-seeded experiments onsisted of four tretments (untreted ontrol nd one, two, or four pplitions of lmd-yhlothrin) rrnged s rndomized omplete lok with four replitions. Plot size in these two experiments ws 1.25m y 5.5m, nd plots were surrounded y metl flshing to restrit movement of insetiides mong plots. Permnent floods were pplied on 11 Apr nd My for the two experiments. Rie plnts possessed four true leves t flooding in oth experiments. Lmd-yhlothrin pplitions were mde y kpk spryer to pproprite plots in oth experiments one df (single lmd-yhlothrin tretment), one nd seven df (two lmd-yhlothrin pplitions), nd one df nd every four to five dys therefter (four lmd-yhlothrin pplitions). Core smpling dtes for eh experiment were s follows (four or five ore smples from eh plot on eh dte): erly plnting, 7 My (26 df) nd 17 My (36 df); mid plnting, 5 Jun (26 df) nd 14 Jun (35 df). Sttistil Anlyses Rie wter weevil ounts from two to five ore smples per plot per smpling dte were verged to otin men density (lrve nd pupe per ore smple). Men lrvl/pupl densities were nlyzed y mixed-effets liner model ANOVA using PROC MIXED in SAS [2] s pproprite for split-plot experimentl design (plnting dte nd insetiide tretment s fixed effets, lok s rndom effet) or rndomized lok design (insetiide tretment s fixed effet, lok s rndom effet, with dt from eh plnting dte nlyzed seprtely). When ore smples were tken on more thn one osion in n experiment, the dt from eh ore smpling were nlyzed seprtely. Yield dt were nlyzed similrly using PROC MIXED in SAS. Mens were seprted using Tukey-Krmer men omprisons. RESULTS Split-Plot Studies: 21 nd experiment: There ws signifint trend towrd higher densities of RWW lrve nd pupe t lter plnting dtes in 21 (Tle 2, Fig. 1). This trend ws evident in ore smples tken three nd five weeks fter flooding (first nd seond ore smplings), lthough the min effet of plnting dte ws signifint only for ore smples tken five weeks fter flooding (Tle 2). Tretment of seeds with the insetiide fipronil resulted in signifint redution in weevil densities in ore smples tken t oth three nd five weeks fter flooding (Tle 2). However, signifint insetiide y plnting dte intertion for oth the three- nd five-week ore smplings indites tht the effet of insetiide vried with plnting dte. For the three-week ore smpling, differenes in weevil densities etween treted nd untreted suplots were signifint only for the lte plnting dte, ut for ore smples tken five weeks fter flooding, differenes in weevil densities etween insetiide-treted nd untreted suplots were signifint for ll three plnting dtes (Fig. 1). For the five-week ore smplings, the solute differenes in lrvl densities etween treted nd untreted plots were gretest in lte plnted plots. When the effiy of insetiidl seed tretments is expressed s perent redution in inset densities, insetiide effetiveness ws greter t the erly plnting dte: redution in inset densities exeeded 86% t the erly plnting dte, nd verged out 8% t the mid- nd lte plnting dtes. Yields in 21 were signifintly higher from plots plnted t the erly plnting dte thn from plots plnted t either the mid- or lte plnting dte (Fig. 1, Tle 2). Yields from insetiide-treted plots were higher thn yields from untreted plots t the erly nd lte plnting dtes ut not t the mid plnting dte. Perent differenes in yields etween insetiide-treted nd untreted plots were higher t the lte plnting dte (27.6%) thn t the erly plnting dte (12.7%). 28 experiment: The min plot effet of plnting dte ws signifint for ore smples tken 26 df nd mrginlly signifint for ore smples tken df, inditing tht overll densities of RWW lrve nd pupe were higher in lte plnted suplots thn in erly plnted suplots (Tle 2, Fig. 2). However, differenes in weevil densities in untreted plots were smll; it ws in the insetiide-treted suplots tht the plnting dte effet ws most evident. Tretment of plots with insetiides signifintly redued overll weevil densities t oth 26 df nd df. Moreover, the effet of insetiide tretment differed with plnting dte in oth Tle 2. Anlysis of Vrine of Lrvl Densities (Lrve nd Pupe Per Core Smple) nd of Yields from Split-Plot Experiments Designed to Investigte the Effets of Plnting Dte in 21 nd 28, LSU AgCenter Rie Reserh Sttion, Crowley, Louisin Soure of Vrition Core Smpling 1 Core Smpling 2 Yields df F P df F P df F P 21 experiment plnting dte (pd) 2, , , <.1 Insetiide tretment (t) 1, <.1 1, <.1 1, <.1 pd x t 2, , , experiment plnting dte (pd) 1, , , Insetiide tretment (t) 3, <.1 3, <.1 3, pd x t 3, , ,

5 Plnting Dte nd Rie Wter Weevils in Louisin The Open Entomology Journl, 211, Volume Weevil lrve + pupe per ore Core smples: 21 d post-flood Untreted Ion-treted 27 Mrh 9 April 3 April Weevil lrve + pupe per ore Core smples: dys fter flooding Untreted Ion-treted 27 Mrh 9 April 3 April Plnting dte Plnting dte 1 Adjusted grin yields in kg per h Yields d Plnting dte Untreted Ion-treted 27 Mrh 9 April 3 April d d Fig. (1). Influene of plnting dte nd insetiide tretment on densities of rie wter weevil lrve nd pupe (1, 1) nd on grin yields (1) in plnting dte experiment onduted in 21 t the LSU AgCenter Rie Reserh Sttion, Crowley, Louisin. Densities of rie wter weevil lrve nd pupe (lrve nd pupe per ore smple + s.e.) were determined 21 (1) nd dys fter flooding (1) for eh plnting dte. Brs ompnied y different letters designte mens tht differed signifintly (Tukey s men seprtion). the 26 d nd df ore smples. For ore smples tken 26 df, insetiide tretments (espeilly lmd-yhlothrin pplitions) were more effetive t reduing weevil densities in erly plnted suplots thn in lte plnted suplots (Fig. 2). Similrly, for ore smples tken df, single pplitions of lmd-yhlothrin were more effetive in erly plnted suplots thn in lte plnted suplots (Fig. 2). The nlysis of the 28 yield dt showed tht suplot yields were signifintly ffeted y plnting dte (Tle 2). Overll, yields were higher from erly plnted suplots thn from lte plnted suplots. At the erly plnting dte, there were no signifint differenes (s indited y Tukey- Krmer omprisons) in yields mong untreted nd insetiide-treted plots. At the lte plnting dte, however, yields were highest from Dermor X--treted plots, intermedite from plots treted twie with lmd-yhlothrin, nd lowest in untreted plots nd plots treted one with lmdyhlothrin. Seprte Rndomized Complete Blok Studies: 23, 24, nd 27 Studies in 23, 24 nd 27 onsisted of seprte rndomized lok experiments plnted t two, three or four dtes. Replition of insetiide tretments within eh plnting dte experiment llowed sttistil nlyses of the effet of insetiide tretment for eh experiment, ut lk of replition of plnting dte in these experiments preluded nything more thn qulittive nlysis of the effet of plnting dte. 23 experiments: Weevil densities in untreted plots were similr mong plnting dtes in 23 (Tle 3). Tretment of seeds with fipronil redued densities of weevil lrve nd pupe 25 to 27 df t the erly nd mid plnting dtes ut not t the lte plnting dte i.e., the fipronil tretment ws effetive t the first two plnting dtes ut not the lte plnting dte. Yields were signifintly higher from

6 6 The Open Entomology Journl, 211, Volume 5 Stout et l. Weevil lrve + pupe per ore 2 Core smples: 26 dys fter flooding Untreted Krte 1x Krte 2x Dermor ST d 24 Mrh 2 My Plnting dte d Weevil lrve + pupe per ore 2 Core smples: dys fter flooding Mrh 2 My Plnting dte Untreted Krte 1x Krte 2x Dermor ST 2 28 yields Untreted Krte 1x Krte 2x Krte "exlusion" Yields(kg per h) Mrh 2 My Plnting dte Fig. (2). Influene of plnting dte nd insetiide tretment on densities of rie wter weevil lrve nd pupe (2, 2) nd on grin yields (2) in plnting dte experiment onduted in 28 t the LSU AgCenter Rie Reserh Sttion, Crowley, Louisin. Densities of rie wter weevil lrve nd pupe (lrve nd pupe per ore smple + s.e.) were determined 26 dys fter flooding (2) nd dys fter flooding (2) for eh plnting dte. Brs ompnied y different letters designte mens tht differed signifintly (Tukey s men seprtion). Ion-treted thn from untreted plots t the mid nd lte plnting dtes ut not the erly plnting dte. When expressed on perent sis, differenes in yields etween treted nd untreted plots inresed with plnting dte, with 14.7% redution in the erly plnting dte, 22.1% redution t the mid plnting dte, nd 32.9% redution t the lte plnting dte. 24 experiments (wter-seeded): Densities of RWW lrve nd pupe in untreted plots 27 to 29 dys fter flooding were very low in plots plnted on the erliest plnting dte, highest in plots plnted two weeks lter, nd intermedite in plots from the lst two plnting dtes (Tle 3). Tretment of seeds with insetiides signifintly redued weevil densities in plots in ll four experiments (P <.1). Yields were higher from insetiide-treted plots t ll four plnting dtes (Tle 3), ut only for the seond dte ws the differene in yields signifint. 27 experiments: Densities of weevil lrve nd pupe in untreted plots were higher in the experiment plnted on 17 Apr thn in the experiment plnted on 8 Mr, espeilly for the ore smples tken 26 df (Fig. 3). (Densities were higher yet in omprle wter-seeded experiment plnted on 16 My; dt not shown). Insetiide tretment signifintly redued weevil densities in oth the erly nd midplnted experiments (P <.1 for oth experiments for oth ore smplings), ut the ptterns differed etween the two experiments. For the experiment plnted on 8 Mr, one, two, nd four pplitions of lmd-yhlothrin signifintly redued densities of lrve elow densities oserved in untreted plots on the 26 df ore smpling; however, for the 17 Apr plnting, single pplitions of lmd-yhlothrin filed to signifintly redue weevil densities elow those found in untreted plots on the 26 df ore smpling. For the ore smplings tken df, the effiy of four ppli-

7 Plnting Dte nd Rie Wter Weevils in Louisin The Open Entomology Journl, 211, Volume 5 7 Tle 3. Lrvl densities (lrve nd pupe per ore smple ± s.e.), yields (kg per h ± s.e.), nd % yield losses from seprte rndomized lok experiments with different plnting dtes, 23 nd 24, LSU AgCenter Rie Reserh Sttion, Crowley, Louisin. Mens from insetiide-treted plots ompnied y n sterisk re signifintly different thn orresponding mens from untreted plots Dte of Plnting Lrvl Densities, Dys After Flood: Yields in kg h-1 Experiment Untreted Insetiide-treted Untreted (U) Insetiide-treted (I) % Yield Differene [(I U)/I]x 23 (drill-seeded) 25 Mrh 21.2 ± ±.6* 85.2 ± ± % 16 April 19.9 ± ±.3* ± ± 36.1* 22.1% 8 My 17.5 ± ± ± ± 314.4* 32.9% 24 (wter-seeded) 15 Mrh 2. ±.3.13 ±.1* ± ± % 1 April 16.2 ± ± 1.* ± ± 484.8* 29.2% 14 April 12.9 ± ±.4* ± ± % 3 April 11.7 ± ±.5* ± ± % tions of Krte Z ws redued in the experiment plnted on 17 Apr (69% redution reltive to ontrol) ompred to the experiment plnted on 8 Mr (82% redution reltive to ontrol). Yields did not differ with tretment in either the erly or mid-plnted experiment (dt not shown). DISCUSSION Erly plnting filitted weevil mngement in ll five yers of the study. In three of five yers (21, 24, nd 27), densities of RWW lrve nd pupe in plots not treted with insetiide inresed s funtion of plnting dte. In ft, in ll three of these yers, t the erly plnting dtes, densities of weevil lrve nd pupe in intitl ore smples (generlly tken three to four weeks fter flooding) were t or elow levels onsidered to e eonomilly dmging (three to five lrve nd pupe per ore smple), showing tht erly plnting is sometimes mens of voiding dmging infesttions of weevil lrve, or t lest delying suh infesttions until rie is older. Furthermore, ptterns of yields nd yield losses generlly support the ide tht the yield impt of weevil infesttions ws lower in erly plnted rie. In oth 21 nd 28 (the two split-plot experiments from whih the strongest inferenes n e mde), yields were higher from erly plnted plots thn from lte plnted plots, nd yield redutions ttriutle to weevil infesttions were lso lower from erly plnted plots (. 13%) thn from lte plnted plots (19-28%). This pttern ws lso oserved in the seprte rndomized lok experiments onduted in 23 (Tle 3). Finlly, experiments onduted in 27 nd 28 provided evidene tht single pplitions of lmd-yhlothrin were more effetive in reduing densities of weevil lrve nd pupe in erly plnted experiments thn in lte plnted experiments. This is the first report of n effet of plnting dte on insetiide effiy in rie. The ptterns of RWW undne oserved in these experiments re explile y referene to pulished desriptions of RWW ehvior nd iology. Emergene from overwintering y RWWs is, like other proesses in insets, dependent on temperture [5,12]. In prior studies, emergene of weevils from overwintering ws found to egin in lte Mrh in southwest Louisin [5] nd mid-april in Arknss [12,13]. However, weevil emergene from overwintering is protrted proess tht is not omplete until two or more months fter it egins [3,12]. Thus, fields plnted nd flooded suffiiently erly in the seson, when weevil popultions hve not ompletely emerged from overwintering sites, re sujet to infesttion y smller popultions thn re fields plnted nd flooded lter, when ll or nerly ll overwintering weevils hve emerged from overwintering sites. This is likely the primry explntion for smller weevil popultions in erly plnted plots thn lte plnted plots in three of five yers in this study. In ddition, erly plnting of rie my llow rie to develop pst the mid-tillering stge of growth, the stge most preferred for weevil oviposition [17], efore lrge weevil popultion egins infesting rie fields. Pulished informtion out RWW iology lso explins why pplitions of lmd-yhlothrin hd redued effiy in lte plnted fields [7]. One they hve emerged from overwintering sites, RWWs my live for severl months or more, nd my move from field to field to feed nd reprodue [3,18]. Furthermore, weevils my omplete their immture stges within 3 dys [5]. Lte-plnted rie is thus potentilly sujet to infesttion y weevils from three soures (overwintering-genertion weevils rriving from other rie fields, first genertion weevils rriving from other rie fields, nd, perhps, lte-emerging, overwintering-genertion weevils rriving diretly from overwintering sites), wheres erly plnted fields re generlly invded only y weevils rriving diretly from overwintering sites. As result, immigrtion of RWWs to lte plnted fields tends to our sooner fter flooding nd over more extended period of time thn does immigrtion to erly plnted rie [3]. Applitions of pyrethroids like Krte Z, whih hve limited residul tivity, my therefore eliminte lower proportion of dult weevils in lte plnted fields thn in erly plnted fields. Erly plnting hs een suggested s mngement tti for the RWW y numerous uthors over the pst 8 yers [3,, 11, 14, 15]. Initilly, this tti ws viewed only s

8 8 The Open Entomology Journl, 211, Volume 5 Stout et l. 3 3 Weevil lrve + pupe per ore Core smples: 26 dys fter flooding 8 Mrh 17 April Untreted Krte 1x Krte 2x Krte "exlusion" Weevil lrve + pupe per ore Core smples: dys fter flooding 8 Mrh 17 April Untreted Krte 1x Krte 2x Krte "exlusion" Plnting dte Plnting dte Fig. (3). Influene of insetiide tretment on densities of rie wter weevil lrve nd pupe (2, 2) in seprte rndomized lok experiments sown on two dtes in 27 t the LSU AgCenter Rie Reserh Sttion, Crowley, Louisin. Densities of rie wter weevil lrve nd pupe (lrve nd pupe per ore smple + s.e.) were determined 26 dys fter flooding (3) nd dys fter flooding (3) for eh experiment. For eh plnting dte, rs ompnied y different letters designte mens tht differed signifintly (Tukey s men seprtion). mens of reduing weevil popultions in rie fields. In this study s well s prior studies, the hypothesis tht erly plnting is ssoited with lower popultions of weevil lrve in untreted rie hs reeived mixed support [,14,15]; tht is, the pttern is oserved in some yers (e.g., 21) ut not others (e.g., 23). However, in some studies tht did not find lower weevil densities in erly plnted plots (e.g. [14]), rie ws proly not plnted erly enough to result in synhrony etween rie development nd weevil emergene. Thompson et l. [14] introdued the notion tht erly plnted rie ould etter tolerte injury y weevil lrve y showing tht yield redutions were lower in erly plnted rie thn in lte plnted rie in two-yer study. Reently, Espino et l. [15] nlyzed dt from experiments onduted over six-yer period in Texs nd found tht the reltionship etween density of RWW lrve nd pupe nd yield loss did not vry with plnting dte, result seemingly t odds with tht of Thompson et l. [14]. Our oservtion of redued yield losses (on perent sis) in erly plnted rie in 21 nd 28 is onsistent with the hypothesis tht erly plnted rie is more tolernt of weevil injury thn lte plnted rie, lthough in 21 redued yield losses ould e lso ttriuted to lower lrvl popultions in erly plnted rie. Rie ppers to e more tolernt of RWW lrvl feeding t lter stges of plnt development thn t erlier stges of development [19], perhps explining why erly plnted rie, in whih infesttion y weevil lrve is sometimes delyed until rie plnts re older, in some ses ppers to e more tolernt of weevil injury. However, it is diffiult to disentngle the overll positive effets of erly plnting on rie yield [15] from puttive inrese in tolerne to RWW injury in erly plnted rie, nd more reserh will e required to lrify the impt of erly plnting on rie tolerne to weevil injury. The finding tht single pplition of the pyrethroid lmd-yhlothrin ws not lwys effetive t reduing weevil popultions elow threshold levels when weevil popultions were high (for instne, in lte plnted rie in 27 nd in oth erly nd lte plnted rie in 28) hs importnt implitions for RWW mngement progrms. First, this result provides dditionl justifition for plnting rie erly (within the rnge of reommended plnting dtes): euse weevil popultions re more likely to e low in erly plnted rie, erly plnting potentilly llows frmers wider hoie of effetive insetiides. Furthermore, this result demonstrtes tht, when plnting rie lte, rie frmers should use seed tretments rther thn folir pplitions of pyrethroids for weevil mngement, euse weevil popultions re often high in lte plnted rie nd pplitions of pyrethroids hve redued effiy under suh onditions. Reently, two seed tretments (Dermor X- nd CruiserMxx ) hve een registered for use in rie nd hve proven effetive in smll-plot nd ommeril-sle trils (Stout nd Hummel, unpulished dt). CONCLUSIONS The results of this study provide evidene tht plnting rie erlier within the reommended rnge of plnting dtes ontriutes to weevil mngement in three wys. First, erly plnted rie is often sujet to lower levels of infesttion. Seond, erly plnted fields sometimes suffer lower yield losses from weevils, perhps euse plnting rie erly in the reommended plnting window llows rie to grow pst the most suseptile growth stges efore migrtion of weevils from overwintering sites. Third, erly plnting llows greter flexiility in use of insetiides. Erly-plnted fields

9 Plnting Dte nd Rie Wter Weevils in Louisin The Open Entomology Journl, 211, Volume 5 9 n e effetively treted with folir insetiides, whih re muh more ffordle tretment option thn seed tretment lterntives. ACKNOWLEDGMENTS The uthors thnk Dr. D. Blouin for dvie on sttistis, Mr. Ryn Pousson for ssistne with experiments, nd five nonymous reviewers for omments on previous drft of the mnusript. This reserh ws supported y grnts to MJS from the Louisin Rie Reserh Bord nd the USDA Biologilly Bsed Pest Mngement nd Pest Mngement Alterntive Progrms. ABBREVIATION df = dys fter flooding REFERENCES [1] Wy MO. Inset pest mngement in rie in the United Sttes, In: Gryson BT, Green MB, Copping LG, Eds. Pest mngement in Rie. Brking, UK: Elsevier Applied Siene Pulishers 199; pp [2] Sito T, Hiri K, Wy MO. The rie wter weevil, Lissorhoptrus oryzophilus Kushel (Coleopter: Curulionide). Appl Entomol Zool 25; 4: [3] Shng H, Stout MJ, Zhng Z, Cheng J. Rie wter weevil (Coleopter:Curulionide) popultion dynmis in Louisin. J Entomol Si 24; 39: [4] Stout MJ, Riggio MR, Zou L, Roerts R. Flooding influenes ovipositionl nd feeding ehvior of the rie wter weevil (Coleopter:Curulionide). J. Eon Entomol 22; 95: [5] Zou L, Stout MJ, Ring DR. Degree-dy models for emergene nd development of the rie wter weevil (Coleopter: Curulionide) in southwestern Louisin. Environ Entomol 24; 33: [6] Zou L, Stout MJ, Dunnd RT. The effets of feeding y the rie wter weevil, Lissorhoptrus oryzophilus Kushel, on the growth nd yield omponents of rie, Oryz stiv. Agri For Entomol 24; 6: [7] Stout MJ, Rie WC, Riggio RM, Ring DR. The effets of four insetiides on the popultion dynmis of the rie wter weevil, Lissorhoptrus oryzophilus Kushel. J Entomol Si 2; 35: [8] Hummel N, Stout MJ. Rie wter weevil ontrol with Dermor X- seed tretment, 28. Arthropod Mngement Tests 28 [seril on the internet]. Aville from: [9] Stout MJ, Frey MJ. Evlution of thimethoxm s seed tretment ginst the rie wter weevil. Ann Res Rpt Rie Res Stn LSU Agri Ctr 27; 99: [] Isley D. Shwrdt HH. The rie wter weevil. Arknss Agriulturl Experiment Sttion Bulletin 1934; 299: [11] Bowling CC. Inset pests of rie in the United Sttes, In: The mjor inset pests of the rie plnt. Proeedings, Symposium Interntionl Rie Reserh Institute, Los Bntos, Philipines, Septemer Johns Hopkins Press, Bltimore, MD, 1967; [12] Morgn DR, Slymker PH, Roinson JF, Tugwell NP. Rie wter weevil (Coleoptern: Curulionide) indiret flight musle development nd spring emergene in response to temperture. Environ Entomol 1984; 13: [13] Mud ARB, Tugwell NP, Hizlip MB. Sesonl history nd indiret flight musle degenertion in the rie wter weevil. Environ Entomol 1981; : [14] Thompson RA, Quisenerry SS, N guessn FK, Hegler AM, Giesler G. Plnting dte s potentil ulturl method for mnging the rie wter weevil (Coleopter: Curulionide) in wterseeded rie in southwest Louisin. J Eon Entomol 1994; 87: [15] Espino L, Wy MO, Person R, Nunez M. Effet of plnting dte on Lissorhoptrus oryzophilus (Coleopter Curulionide) density yield reltionship on rie in southestern Texs. J Eon Entomol 29; 2: [16] Blnhe B, Hrrell D, Sihuk J. Generl gronomi guidelines. In: Louisin rie prodution hndook, Sihuk J Ed. LSU Agri Ctr Pul 2321, LSU AgCenter, Bton Rouge, LA, 29; [17] Bng YH, Tugwell NP. Adult rie wter weevil feeding preferenes for rie plnts nd leves of different ges. Arknss Agriulturl Experiment Sttion. Rep Ser 231, 1976; [18] Nilkhe SS. Reprodutive sttus of overwintering rie wter weevils. Ann Entomol So Am 1977; 7: [19] Stout MJ, Rie WC, Ring DR. The influene of plnt ge on the tolerne of rie to injury y the rie wter weevil. Bull Entomol Res 22; 92: [2] SAS Institute. SAS/STAT User s guide, relese 9.1. SAS Institute, Cry, North Crolin 24. Reeived: Mrh 11, 2 Revised: August 6, 2 Aepted: Otoer 6, 2 Stout et l.; Liensee Benthm Open. This is n open ess rtile liensed under the terms of the Cretive Commons Attriution Non-Commeril Liense ( whih permits unrestrited, non-ommeril use, distriution nd reprodution in ny medium, provided the work is properly ited.