Effect of Maize Hybrid and Foliar Fungicides on Yield Under Low Foliar Disease Severity Conditions

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1 Disese Control nd Pest Mngement Effect of Mize Hyrid nd Folir Fungicides on Yield Under Low Folir Disese Severity Conditions Slly O. Mllow, Pul D. Esker, Pierce A. Pul, Crl A. Brdley, Venkt R. Chpr, Shwn P. Conley, nd Alison E. Roertson First nd seventh uthors: Deprtment of Plnt Pthology nd Microiology, Iow Stte University; second uthor: Escuel de Agronomí, Universidd de Cost Ric; third uthor: Deprtment of Plnt Pthology, Ohio Stte University; fourth nd fifth uthor: Deprtment of Crop Sciences, University of Illinois t Urn-Chmpign; nd sixth uthor: Deprtment of Agronomy, University of Wisconsin. Accepted for puliction 2 Mrch ABSTRACT Mllow, S. O., Esker, P. D., Pul, P. A., Brdley, C. A., Chpr, V. R., Conley, S. P., nd Roertson, A. E Effect of mize hyrid nd folir fungicides on yield under low folir disese severity conditions. Phytopthology 105: Folir fungicide use in the U.S. Corn Belt incresed in the lst decde; however, questions persist pertining to its vlue nd sustinility. Multistte field trils were estlished from 2010 to 2012 in Illinois, Iow, Ohio, nd Wisconsin to exmine how hyrid nd folir fungicide influenced disese intensity nd yield. The experimentl design ws in split-split plot with min plots consisting of hyrids vrying in resistnce to gry lef spot (cused y Cercospor zee-mydis) nd northern corn lef light (cused y Setospher turcic), suplots corresponding to four ppliction timings of the fungicide pyrclostroin, nd su-suplots represented y inocultions with either C. zee-mydis, S. turcic, or oth t two vegettive growth stges. Fungicide ppliction (VT/R1) significntly reduced totl disese severity reltive to the control in five of eight site-yers (P < 0.05). Disese ws reduced y pproximtely 30% t Wisconsin in 2011, 20% t Illinois in 2010, 29% t Iow in 2010, nd 32 nd 30% t Ohio in 2010 nd 2012, respectively. These disese severities rnged from 0.2 to 0.3% in Wisconsin in 2011 to 16.7 to 22.1% in Illinois in The untreted control hd significntly lower yield (P < 0.05) thn the fungicide-treted in three site-yers. Fungicide ppliction incresed the yield y pproximtely 6% t Ohio in 2010, 5% t Wisconsin in 2010 nd 6% in Yield differences rnged from 8,403 to 8,890 kg/h in Wisconsin 2011 to 11,362 to 11,919 kg/h in Wisconsin Results suggest susceptiility to disese nd previling environment re importnt drivers of oserved differences. Yield increses s result of the physiologicl enefits of plnt helth enefits under low disese were not consistent. During the pst decde, mize (Ze mys L.) production in the U.S. Corn Belt hs seen n increse in the use of folir fungicides (Munkvold et l. 2008). Previously, the ppliction of folir fungicides to mize ws rre, since the yield response ws not sufficient to economiclly offset the cost of the fungicide (Munkvold et l. 2001; Pul et l. 2011; Wegulo et l. 1997). In recent yers, however, high grin prices hve led to incresed lnd re under mize production. Purported yield enhncement ssocited with quinone outside inhiitors (QoI; sometimes referred to s stroilurins) hve encourged the use of folir fungicides (Brdley 2012). Mize is susceptile to severl folir fungl spot nd light diseses (Blint-Kurti nd Johl 2009; White 1999), including gry lef spot (GLS), cused y Cercospor zee-mydis, (nmorph) nd northern corn lef light (NCLB), cused y Setospher turcic teleomorph (Exserohilum turcicum nmorph). Trditionlly, resistnt hyrids or cropping prctices, such s crop rottion nd tillge, hve een successfully used to mnge these diseses. However, over the pst two decdes, miniml rottion nd reduced or no-tillge hve incresed residue (Booslis et l. 1986) nd incresed the risk of residue-orne disese-driven yield loss in mize, thus leding to greter interest in folir fungicides (Wise nd Mueller 2011). While fungicide use on corn ws rre prior to 2002, nd unreported y the U.S. Deprtment of Agriculture until 2005, Munkvold et l. (2008) estimted fungicide use t pproximtely 18% of crege plnted in the mjor corn producing sttes in tht yer. In 2010 the Corresponding uthor: S. Mllow; E-mil ddress: sllymllow@gmil.com *The e-xtr logo stnds for electronic extr nd indictes tht one supplementry tle is pulished online The Americn Phytopthologicl Society fungicide-spryed crege ws estimted to e pproximtely 10% of crege plnted (Bttglin et l. 2011; Munkvold et l. 2001, Munkvold et l. 2008; Wise nd Mueller 2011). The decision to pply folir fungicide to mize is usully sed on the developmentl stge of the crop, environmentl fctors, the susceptiility of the host, nd disese severity (Nelson nd Meinhrdt 2011). The effectiveness of such pplictions lrgely depends on their timing (Wrd et l. 1997). Current recommendtions re for ppliction of folir fungicides to mize t nthesis-crop development stges VT to R1 (Aendroth et l. 2011). These re sed on the use of mesure tht leds to the defining of chrcteristics for when to spry, i.e., disese threshold of 5% severity on the third lef elow the er lef nd ove on 50% of the plnts in the field t nthesis (Munkvold 1997). The rnge of crop development stges VT to R1 covers tssel emergence, silking, pollintion, nd fertiliztion. Thus, the numer of hrvestle kernels is determined nd is function of conditions during this period (Aendroth et l. 2011). A fungicide ppliction t the R2/R3 (lister/milk) crop developmentl stges provides protection from fungl infection to the leves in the upper cnopy nd ensures their continued photosynthetic ctivity through to the R4/R5 (Munkvold 1997) crop developmentl stges while grin fill tkes plce (Aendroth et l. 2011). Most of the VT/R1 threshold-sed fungicide ppliction guidelines were developed in the 1990s for DeMethyltion Inhiitor (DMI) fungicides (Munkvold 1997; Munkvold et l. 2001). In the pst decde, however, severl new clsses of fungicides with different modes of ction, including stroilurin nd succinte dehydrogense inhiitor (SDHI) fungicides, hve een registered for use on mize in the United Sttes (Hewitt 1998). Another fctor responsile for incresed fungicide use since 2007 is the mrketing of stroilurins for yield enhncement in the sence ofdisese (Brtlettet l. 2002; Venâncio et l. 2003). Yield 1080 PHYTOPATHOLOGY

2 enhncement hs een ttriuted to physiologicl effects (plnt helth enefits) relted to greter wter nd nitrogen use efficiency (Ruske et l. 2003), incresed ntioxidnt ctivity (Wu nd Von Tiedemnn 2002), delyed lef senescence, nd incresed stnd-ility of mize t hrvest (Venâncio et l. 2003; Wise nd Mueller 2011). Questions regrding the frequency of positive yield response, economic enefit nd justifiction for this use of fungicides, sometimes t the expense of other vile disese mngement options, however hve een rised (Cost et l. 2012; Munkvold et l. 2001; Pul et l. 2011). In order to ensure sufficient sustinility, stroilurin fungicides should e prt of n IPM system tht minimizes the risk of development of resistnt supopultions of the pthogens eing mnged (Brent nd Hollomon 2007; Vincelli 2002). Pul et l. (2011) used met-nlysis to synthesize reserch findings from multiple individul trils (2002 to 2009) with multiple vriles (hyrid, environment, tril design, nd fungicides) on mize response to the most widely used folir fungicides. These nlyses indicted positive yield response even t low disese though this ws not lwys economiclly eneficil. Therefore, the ojective of the current study ws to develop model within n IPM frmework tht could e used to determine how different disese intensities ffect mize yield nd how different mngement tctics (resistnce nd fungicide ppliction) my mitigte these effects. We hypothesized tht depending on the mize hyrid nd environment, folir nd stlk diseses my influence grin yield individully or in comintion. This effect of diseses on yield my in turn influence the economic vlue of using folir fungicide. To test these hypotheses, coordinted field experiments were conducted in Illinois, Iow, Ohio, nd Wisconsin. The novelty of our pproch ws in the use of the sme hyrids, fungicide, nd its ppliction timing nd inocultion t ll loctions with the specific ojectives of investigting (i) the effects of fungicide ppliction timing on the intensities of folir disese nd stlk rot development nd (ii) yield response in hyrid mize with vrying levels of resistnce to folir diseses. MATERIALS AND METHODS Multistte field trils were estlished from 2010 to 2012 t the following loctions: University of Illinois Crop Sciences Reserch nd Eduction Center ner Chmpign, IL in 2010 nd 2011 ( , _ ), Iow Stte University South Woodruff Frm ner Npier, IA in 2010 nd 2011 ( , _ ), University of Wisconsin Arlington Agriculturl Reserch Sttion ner Arlington, WI in 2010 nd 2011 ( , _ ), the Ohio Stte University Beef nd Sheep Reserch Unit, Wooster, OH in 2010, ( , ), nd Western Agriculturl Reserch Sttion ner South Chrleston, OH in 2012 ( , ). Trils were plnted etween dys 125 nd 139 of the yer (5 to 20 My), with the exception of the tril t Wooster, OH in 2010, which ws plnted on dy 145 (25 My) of the yer (Tle 1). Rinfll, reltive humidity (%), nd dily temperture dt for the months of My to Octoer for ll siteyers were downloded from the NOAA wesite for the irport nerest to the loction (ccessed 20 Septemer 2013). Dt on the 30-yer verge (norml) (Environment Cnd, 2011) for the sme prmeters ws lso noted. All trils were estlished in no to minimum-tilled fields plnted with mize the previous growing seson, mimicking conservtiontillge/continuous-mize cropping system. Trils were mnged ccording to locl University extension recommendtions relted to gronomic prctices (Dodd 1980; Mueller nd Sisson 2013; Nfziger 2009; Thomison et l. 2005). The experimentl design ws rndomized complete lock with split-split-plot rrngement of hyrid, fungicide tretment, nd inocultion in four replicte locks. The whole plot tretment ws hyrid (four levels; two levels in Ohio 2012), the suplot ws fungicide ppliction timing (four levels), nd the su-suplot ws inocultion tretments (10 levels), herefter referred to s the plot. Ech plot consisted of four 7.62-mlong rows, spced 76.2 cm prt. There were totl of 640 plots t ech site-yer, except for Ohio 2012 with 320 plots. Four yellow dent corn hyrids, differing in levels of prtil resistnce to GLS nd multigenic resistnce to NCLB, were otined from DuPont Pioneer Hi-Bred Interntionl (Johnston, IA): (i) P0461XR (104 dys to comprtive reltive mturity [CRM 104 dys], nd susceptile to GLS nd NCLB, (ii) P0891XR (CRM 108 dys nd resistnt to GLS nd NCLB), (iii) P35F44 (CRM 105 dys, resistnt to NCLB nd susceptile to GLS), nd (iv) P33W84 (CRM 111 dys, resistnt to GLS nd susceptile to NCLB). All four hyrids were plnted in ll site-yers, except for Ohio in 2012 when only P0891XR nd P0461XR were plnted. The following fungicide tretments were evluted: n untreted control (UTC), single ppliction of Hedline (pyrclostroin, BASF, Reserch Tringle Prk, NC) mde (i) etween nthesis nd silking (VT/R1) stges (Aendroth et l. 2011), or (ii) etween lister nd milk (R2 to R3, respectively) stges, or (iii) using folir disese severity threshold (T). The threshold-sed pplictions were mde when GLS or NCLB lesions were oserved on the third lef elow the er or ove on 50% of the plnts in the suplot (Munkvold 1997). At the Ohio loction in 2010, there were three replictes of the threshold tretment, while in Wisconsin tril in 2011, no threshold tretment ws pplied since the threshold ws not oserved; therefore, this tretment ws considered s nother repliction of the untreted control. Ech suplot ws divided into 10 four-row plots tht were inoculted with different comintions of C. zee-mydis nd S. turcic etween crop development stges V6 nd V12 to ensure pthogen presence nd increse the chnces of infection. In Iow nd Ohio, plots were inoculted either t V6, V9, or t oth V6 nd V9, wheres in Illinois nd Wisconsin, plots were inoculted either t V9, V12, or t oth V9 nd V12. Inocultion tretments consisted of noninfested sterilized grin (UTC), sterilized grin infested with C. zee-mydis lone, S. turcic lone, or 1:1 mixture of sterilized grin infested with C. zee-mydis nd S. turcic. Inoculum ws prepred s previously descried (Venâncio et l. 2003), using sorghum (Sorghum icolor) s the crrier, except in Ohio where white millet (Pnicum miliceum) ws used (Wllhed 2012). Approximtely 18 to 20 kernels of infested grin inoculum were dispensed into the whorl of TABLE 1. Min tril informtion, Julin dy (JD) when the tril ws plnted nd dys fter plnting when disese ssessment nd fungicide ppliction ws done in the field trils conducted etween 2010 to 2012 (old vlues correspond to oservtion dtes used in the nlysis) Disese ssessments (dys fter plnting) Fungicide ppliction (dys fter plnting) Site Yer JD VT/R1 R2/R3 T T c Illinois NA Iow Ohio NA NA NA NA Wisconsin NA Stroilurin fungicide used ws Hedline (pyrclostroin), BASF, Reserch Tringle Prk, NC. Tretments were s follows: UTC, n untreted control; VT/R1, single ppliction of stroilurin fungicide pplied t nthesis; R2/R3, single ppliction pplied t lister/milk growth stge; nd T, single ppliction pplied sed on threshold folir disese severity defined s 5% disese severity on the third lef elow the er lef or ove on 50% of the plnts in the plot. The tril ws repeted in 2011 in Iow, Illinois, nd Wisconsin nd 2012 in Ohio. c In Iow 2011 nd Ohio 2010 sites, disese in some threshold plots developed lter nd consequently these plots were spryed lter. Vol. 105, No. 8,

3 ech plnt in the two center rows of ech plot t the pproprite crop development stges. Folir disese severity ssessments. Folir disese severity ws ssessed in ll plots. The numer of disese ssessments vried y tril, rnging from single ssessment in oth yers in Ohio, two in Illinois in 2010, nd three t ll other site-yers. The dte nd growth stge t which disese severity ws ssessed lso vried mong sites (Tle 1), rnging from 55 to 116 dys fter plnting (dp), which corresponded to crop developmentl stges R1 nd R5, respectively. For the purpose of dt nlysis nd tretment comprison, disese ssessment dt from 80 to 93 dp (pproximte crop developmentl stge erly R5) were used in 2010, nd 103 nd 116 dp (pproximte crop developmentl stge mid to lte R5) in 2011 nd Plots were evluted y quntifying disese severity (percent lef re covered with lesions) on the er lef, one lef ove the er lef nd one lef elow the er lef. Severity of NCLB nd GLS were ssessed seprtely in oth yers in Iow nd Wisconsin, nd in 2010 in Ohio. Notes were tken on severl other folir diseses including nthrcnose lef light (cused y Colletotrichum grminicol), common rust (cused y Puccini sorghi), nd eyespot (cused y Ktiell zee) (dt not shown). In Illinois in 2010 nd 2011, nd Ohio in 2012, composite mesure of disese severity ws done y quntifying the percent lef re covered y lesions of ll folir diseses present; NCLB ws the predominnt disese in Ohio in Stlk rot ssessments. At physiologicl mturity (R6), stlk rot severity ws estimted on three or six consecutive plnts in ech of the two center rows of ech plot, depending on stte. Plnts in ech plot were destructively smpled nd split longitudinlly from the er down to the soil line nd stlk rot severity ws ssessed using 0 to 5 rting scle (0 = no stlk rot evident nd 5 = complete destruction of the pith with lodging elow the er), similr to tht used y Hines (2007). Assessments of plots were mde on conditionl sis mening tht control plots were ssessed first. If stlk rot severity ws, on verge, equl to rting of 2 or higher, the rest of the plots were ssessed, nd if not, no further ssessments were mde. All plots were scored t Iow in 2010, t Illinois in 2010 nd 2011, nd only control plots were rted t Iow in 2011, t Ohio in 2010, nd t Wisconsin in Yield ssessments. After physiologicl mturity (crop developmentl stge R6), the remining plnts in the two center rows of ech plot were hrvested using plot comine with scle nd grin moisture sensor instlled. Yields were converted to kilogrms per hectre nd were stndrdized to 15.5% moisture. Sttisticl nlyses. Dt were nlyzed using PROC GLIMMIX of SAS v. 9.2 (SAS Institute, Cry, NC) (Littell et l. 2006) to exmine the effect of the different tretments on oth disese severity nd yield. Explortory nlyses indicted lrge vritions cross trils; therefore, ech individul site-yer ws nlyzed seprtely. For ll nlyses the level of significnce ws set to 5% ( = 0.05) nd Fisher s protected lest significnt difference (LSD) ws used to compre tretments. Furthermore, when significnt interctions were found, the SLICE option in SAS ws used to exmine these t the level of ech min effect. Grphicl methods including oxplots nd histogrms were used to visulize mens strtified y hyrid, fungicide, inocultion, nd/or their interctions. Correltion ws tested for the ssocition etween folir disese nd stlk rot. Results from the explortory nlysis showed tht the use of squre-root or logit trnsformtion did not reduce the overdispersion of zero s oserved in scores for the two diseses (GLS nd NCLB). Therefore, disese severity dt were nlyzed without trnsformtion. For finl models, hyrid, fungicide timing, nd inocultion were considered fixed effects, while repliction nd whole plot nd suplot errors were considered rndom effects. Due to missing oservtions, degrees of freedom were clculted sed on the Kenwrd-Rogers method (Littell et l. 2006). RESULTS Wether dt summry. The verge monthly trends during the period of ech tril for rinfll, temperture, nd reltive humidity re presented in Tle 2. The 30-yer verge (norml) wether dt used in this study were from wether sttions ner ech site. Emphsis ws plced on July nd August when fungicide ppliction nd most disese rtings were done. Temperture verges rnged from 22.8 to 25.0 C in July nd August 2010, nd etween 18.6 nd 25.6 C in July nd August Rinflls were norml, except for Wisconsin 2010 with 203 mm in July nd Iow 2010 with 381 mm in August tht were ove norml, while in Illinois 2011 August rinfll t 37 mm ws elow verge. In 2010, the temperture in June nd July ws ner norml, while in August, Septemer, nd Octoer tempertures were ove norml cross the four sttes, except for Wisconsin where n erly frost occurred. In June 2010, rinfll ws ove norml in Iow nd some plots flooded resulting in uneven growth in the tril. In August, rinfll ws ove norml in Iow nd Wisconsin. The second yer of the study strted with ove norml rinfll in Iow, Illinois, nd Ohio in My; however, it ws 75% of the norml in Wisconsin. In Iow nd Illinois the rinfll ws ove norml in June nd elow norml in Ohio. July ws drier thn norml t ll sites nd this continued through August in Iow nd Illinois; however the rinfll ws ove norml in Wisconsin nd norml in Ohio. At ll loctions, June tempertures were slightly elow norml. Conditions in July throughout the region were wrmer thn norml, nd this trend continued through Septemer. Wrm windy conditions were prevlent t ll loctions in Octoer. The 2012 growing seson in Ohio ws chrcterized y wrm nd dry conditions, nd the dily men temperture (25.5 C) in July ws the wrmest since Folir disese. The totl men severity of oth diseses (GLS nd NCLB) ws comined for the different tretments. There were no sttisticlly significnt three-wy interctions of fixed effects t ny site-yer, nor two-wy interctions of fungicide ppliction y inocultion, nd hyrid y fungicide ppliction oserved for the disese severity (Tle 3 nd Supplementry Tle S1). However, significnt effect of the hyrid y inocultion interction on disese ws oserved t Illinois in 2010, t Ohio in 2010, nd t Ohio in 2012 (P < , P < , nd P = , respectively). Hyrid P0461XR (susceptile to oth GLS nd NCLB) when inoculted with oth pthogens consistently hd higher disese severity thn the other hyrid y inocultion comintions. At Illinois in 2010, the noninoculted control hd the lowest levels of disese, significntly lower thn in the inoculted tretments for ll the hyrids. At Ohio in 2010 (P < ), there ws no significnt difference in men disese severity etween C. zee-mydis inoculted tretments ( P35F44 1.1%, P33W84 0.2%, P0461XR 0.7%, nd P0891XR 0.5%) nd noninoculted tretments for ny hyrid ( P35F44 0.2%, P33W84 0.1%, P0461XR 0.4%, nd P0891XR 0.1%). However, inocultion with S. turcic resulted in significntly higher men disese severity ( P35F44 6.4%, P33W84 4.9%, P0461XR 8.0%, nd P0891XR 1.6%) when compred with the noninoculted control or plnts inoculted with C. zee-mydis lone. Similrly, t Ohio in 2012 (P = ), the noninoculted control hd less disese in two of the hyrids, P0461XR (4.3%) nd P0891XR (2.3%), lthough this tretment ws only significntly different from the inocultion tretment with oth C. zee-mydis nd S. turcic pthogens in hyrid P0461XR with susceptiility to oth GLS nd NCLB (11.9%; P = ) (Fig. 1). Tle 3 summrizes P vlues from fixed effects in ll site-yers. Trils in which P < 0.05 re olded indicte differences in tretments nd thus emphsize fctors tht could drive interctions oserved. In the cse of Illinois in 2010, Ohio in 2010, nd Ohio in 2012, hyrid, fungicide, nd inocultion ffected disese severity PHYTOPATHOLOGY

4 A significnt effect of fungicide on disese ws oserved t Iow in 2010 (P = ) nd t Wisconsin in 2011 (P = ). Inocultion hd significnt effect on severity t Iow in 2011 (P = ). In 2010, men folir disese severity cross hyrids ws low (<5%) in Iow, Ohio, nd Wisconsin ut considerly higher in Illinois (11 to 30%). In the second yer folir disese severity rnged from 2 to 23% t Illinois in 2011; however it ws generlly lower, <2%, cross ll tretments t Iow in 2011, t Wisconsin in 2011, nd t Ohio in 2012, (Fig. 2). Disese severity in ll trils ws generlly low, <25%, in ll sites. Fungicide ppliction ffected disese in Iow (P = ), Illinois (P < ), nd Ohio (P = ) in 2010, Wisconsin (P = ) in 2011, nd Ohio (P = ) in The percent disese reduction ws often quite smll (Fig. 3). An ppliction of fungicide t VT/R1 reduced disese severity more thn those t R2 to R3, t disese threshold nd the untreted control (Iow, 1.0, 1.3, 1.3, nd 1.4%; Illinois, 16.7, 21.1, 22.1, nd 20.9%; nd Ohio, 1.5, 2.0, 2.0, nd 2.2%, respectively) (Iow, 1.4%; Illinois, 20.9%; nd Ohio, 2.2%). Similrly t Wisconsin in 2011 nd t Ohio in 2012, the highest men disese severity ws oserved in the untreted control (Wisconsin 0.3%, Ohio 5.7%) compred with the fungicide pplied t VT/R1 (Wisconsin 0.2%, Ohio 4.0%) (Fig. 3). Stlk rot. Stlk rot ssessments were mde in ll plots t Iow in 2010, Illinois in 2010 nd Illinois in The disese estimte in control tretments ws extremely low nd did not justify proceeding with further rting in ny plots t Wisconsin in 2011 nd t Ohio in There ws no ssocition etween stlk nd folir diseses s only 1 to 3% of the vrition in stlk rot could e predicted y the folir disese (dt not shown). There ws no effect of fungicide ppliction on stlk rot severity (P = ) t Iow in 2010; however, fungicides pplied t the VT/R1 stge reduced stlk rot severity t Illinois in 2010 (P = ) nd t Illinois in 2011 (P = ) (Tle 4). Hyrid ffected stlk rot t Illinois in 2011, where stlk rot rtings verged 2; the hyrid P0891XR, which is resistnt to GLS nd NCLB, hd sttisticlly higher score thn the other hyrids (Tle 5). Yield. Grin yields were generlly higher in 2011 nd 2012 thn in 2010 in Iow, Illinois nd Ohio loctions (Figs. 4 nd 5). There ws n interction of hyrid y fungicide ppliction on yield t only one site-yer, Wisconsin 2011 (P = 0.005) (Tle 6), where TABLE 2. Monthly verges of wether dt from Ntionl Climtic Dt Center for four sites etween 2010 nd /2012 Month Wether vrile IA IL OH WI IA IL OH WI My PPT (7) (27) Dys RH T (2.7) ( _ 0.7) June PPT (97) (23) Dys RH T (1.6) (1.3) July PPT (3.8) ( _ 58) Dys RH T ( _ 2.33) (5.4) Aug PPT (90) (30) Dys RH T (5.4) (2.0) Septemer PPT (11) (8) Dys RH T (0.1) ( _ 2.0) Octoer PPT (3) ( _ 25) Dys RH T (3.3) The tril ws repeted in 2011 in Iow, Illinois, nd Wisconsin nd 2012 in Ohio. IA, Iow; IL, Illinois; OH, Ohio; nd WI, Wisconsin. Numers in rckets indicte the deprture from norml. PPT, precipittion (rinfll); Dys, numer of dys with rinfll more thn 2.54 mm; RH, reltive humidity (%); nd T, temperture in degrees Celsius. TABLE 3. P vlues summrizing ll fixed effect fctors relted to disese severity (%) per whole plot t four sites etween 2010 nd /2012 Fctors IA IL OH WI IA IL OH c WI d Hyrid < < Fungicide < H F Inocultion < < < H I < < F I H F I The tril ws repeted in 2011 in Iow, Illinois, nd Wisconsin nd 2012 in Ohio. IA, Iow; IL, Illinois; OH, Ohio; nd WI, Wisconsin. Min effects nd their interctions: H, hyrid; F, fungicide; nd I, inocultion. c Ohio 2012, only two hyrids were evluted P0461XR nd P0891XR. d Wisconsin 2011, no threshold fungicide ppliction. Vol. 105, No. 8,

5 greter yields were mesured on P33W84 nd P0461XR with fungicide pplied t VT/R1 or t R2 to R3 compred with the untreted control. At this sme loction, n R2 to R3 fungicide ppliction on P0891XR lso resulted in greter yields thn the control (dt not shown). Hyrid y inocultion ffected yield in only one site-yer, Illinois in 2011 (P = ) (Tle 6), where hyrids with resistnce to NCLB consistently yielded etter thn the susceptile hyrids, nd tretments tht hd inocultions with S. turcic t two different times hd lower yields. In 2010, fungicide ppliction ffected yield in Illinois (P = ), Ohio (P = ), nd Wisconsin (P < ). The untreted control yielded lower thn fungicide-treted plots in Illinois, Ohio, nd Wisconsin (Tle 1). There were no differences with regrd to ppliction timing for these fungicide-treted plots. Similrly, t Wisconsin in 2011 (P = ), the fungicide tretments yielded more thn the untreted control, ut were not different from ech other (Fig. 4). Yield vried y hyrid t Wisconsin in 2010 (P = ) nd t Iow in 2011 (P = ) (Fig. 5). The hyrid with resistnce to GLS, P33W84, hd the highest yields t Wisconsin in 2010 nd t Iow in 2011, while hyrid P0461XR with susceptiility to oth GLS nd NCLB hd the lowest yields. At Illinois in 2011, P35F44, with resistnce to NCLB, hd the gretest yield compred with the other hyrids (P = ) tht were not different from ech other. DISCUSSION We evluted the use of folir fungicides on corn in stndrdized trils conducted in different environments cross four sttes in the Fig. 1. Effect of hyrid nd inocultion (with pthogen Cercospos zee-mydis [CZM] or Setospher turcic [ST] or None or Both) on gry lef spot (GLS) nd northern corn lef light (NCLB) comined disese severity (%) ssessed t the R4/R5 crop developmentl stge, on the er lef of four mize hyrids ( P35F44, resistnt to NCLB; P33W84, resistnt to GLS; P0461XR, susceptile to oth GLS nd NCLB; nd P0891XR, resistnt to oth GLS nd NCLB) grown t three sites etween 2010 nd PHYTOPATHOLOGY

6 U.S. Corn Belt. Our reserch is unique ecuse we used the sme hyrids, fungicide product, nd ppliction timings in ll eight siteyers. Different hyrids, products, or ppliction timing confounds previous reserch tht ssessed folir fungicides on corn. Despite inocultion t erly growth stges to enhnce disese development, finl disese severity in six of the eight site-yers ws low nd strongly influenced y environment nd hyrids. In Illinois, vrition in disese due to hyrid ws moderte while vrition relted to fungicide ppliction ws low. Trils in which fungicide ppliction yielded higher corn yields (sttisticlly significnt) did not necessrily lwys lso hve disese significntly lowered when fungicide ws pplied compred with the nonspryed control. Our dt indicted consistently lower disese severity on resistnt (prtil/incomplete) hyrids, even in situtions where disese severity ws considered very low (<5%). Folir diseses cuse chlorosis nd necrosis tht reduce the photosynthetic ility of leves. The use of folir fungicides is most likely to e profitle when folir disese severity is high (Pul et l. 2011). Nonetheless, while the protection from the ppliction of folir fungicide is similr t low disese severity, mening tht the disese severity is reduced, economiclly it is not likely to e profitle nd therefore hs less direct impct on improving corn production (Johnson 1987). These results re similr to those oserved in trils conducted etween 2002 nd 2009 in 14 sttes (Pul et l. 2011) where the differences in either disese or yield due to fungicide ppliction were highly vrile mong studies. In our trils, fungicide ppliction reduced comined GLS nd NCLB disese severity in four of the eight site-yers, nd n ppliction mde t VT/R1 ws generlly the most effective. These results re consistent with those reported y Nelson nd Meinhrdt (2011), who showed tht the severity of GLS ws reduced y n ppliction of pyrclostroin t VT in four out of six site-yers nd NCLB in one out of six siteyers. The efficcy of fungicide depends on ppliction timing nd is influenced y the mount of disese tht is present in the fields (Coulter 2010;Wise nd Mueller 2011). In our reserch, pplictions mde etween VTnd R1 were the most effective in lowering disese severity under either low or moderte disese conditions. This concurred with previous recommendtions for fungicide ppliction in the United Sttes (Munkvold nd Gormn 2006). However, this reduction in disese did not consistently trnslte into yield enefit. For exmple, in the 2010 nd 2011 Illinois trils, where disese intensity ws considered moderte, there ws reduction in disese severity with fungicide ppliction, ut differences in yield were not sttisticlly significnt (P > 0.05). A similr sitution ws oserved t Iow in 2010 tril, where disese severity ws low nd ws reduced with fungicide ppliction (P = ), ut differences in yield were gin not significnt. One explntion could e due to disese onset occurring lter in the growing seson nd therefore not impcting grin fill. In ddition hyrids with resistnce (incomplete/prtil) to folir diseses cn withstnd the diseses nd show miniml impct on grin fill nd yield even when folir symptoms re present (Wllhed 2012). In our tril only P0461XR hd susceptiility to oth GLS nd NCLB, while the other hyrids hd resistnce to t lest one of the diseses. In nother study, Blndino et l. (2012) reported tht erlier pplictions (V12 to V15, pre-vt) were effective t reducing NCLB when disese severity ws high, while pplictions from VT to R3 were effective in reducing NCLB when disese severity ws low. However, in tht study only pplictions round VT significntly incresed grin yield compred with n Fig. 2. Effect of hyrid on gry lef spot (GLS) nd northern corn lef light (NCLB) disese severity (%) ssessed t the R4/R5 crop developmentl stge, on the er lef of four mize hyrids grown t four sites etween 2010 nd Tril ws repeted in 2011 in Iow, Illinois, nd Wisconsin nd 2012 in Ohio. All hyrids were from DuPont-Pioneer Hi-red Interntionl, Inc. P35, P35F44, susceptile to GLS nd resistnt to NCLB; P33, P33W84, resistnt to GLS nd susceptile to NCLB; P04, P0461XR, susceptile to oth GLS nd NCLB; nd P08, P0891XR, resistnt to oth GLS nd NCLB. IA, Iow; IL, Illinois; OH, Ohio; nd WI, Wisconsin. Ohio 2012, only two hyrids were evluted P0461XR nd P0891XR. Vol. 105, No. 8,

7 untreted control. This emphsizes the influence of the presence of disese nd timing of ppliction on the grin yield when mking comprisons to untreted controls. We did not consistently reduce disese when n ppliction of fungicide ws mde t disese threshold (Munkvold 1997). These results were not ffected y whether the threshold tretment ws met for oth diseses t the sme time, or for individul diseses, s oserved in 2010 t Ohio nd in 2011 t Iow. Shh nd Dillrd (2010), working with sweet corn in New York, reported tht threshold tretment of stroilurin fungicide pplied when 1% of plot hd folir disese, reduced folir disese y 8% compred with the control in susceptile hyrid with up to 60% folir disese severity, ut there ws no yield enefit. The inconsistencies etween our work nd tht of Shh nd Dillrd (2010) could e due, in prt, to the higher susceptiility of sweet corn to folir disese or the threshold eing conservtive. The disese threshold for fungicide ppliction is n re of reserch tht wrrnts further investigtion. The risk of GLS is ffected y plnting dte nd consequently crop growth stge reltive to fvorle wether (Bhti nd Munkvold 2002; Pul nd Munkvold 2005); thus, finl GLS severity my e greter on lte plnted mize compred with mize plnted t the recommended plnting time. Growers in the Corn Belt re plnting erlier compred with the pst (Elmore 2013); consequently crops often rech reproductive stges efore lte July to erly August when wether conditions re more fvorle for folir disese development. Decisions on fungicide ppliction timing should tke into considertion the environment in the current growing seson nd the crop developmentl stge, so tht the fungicide effective period overlps with when the wether is fvorle for disese. It hs een suggested tht fungicide ppliction could led to economic losses if done when disese risk is low (Pul et l. 2011). In our trils, in three of eight site-yers, we oserved n increse in yield when folir fungicides were pplied in the sence of disese control (Illinois 2010, Wisconsin 2010, nd Ohio 2012). QoI fungicides in the U.S. Corn Belt hve een leled for yield enhncing plnt helth enefits (Nelson nd Meinhrdt 2011). Others hve reported greter yields in the sence of disese or TABLE 4. Effect of fungicide on stlk rot disese of corn (0 to 5 scle) ssessed t the R6 physiologicl mturity crop developmentl stge, on the stlks of four mize hyrids grown in Iow nd Illinois etween 2010 nd 2012 Fungicide IA IL IL UTC VT/R R T LSD NS 0.11 NS P vlue Results re presented for stlk rot rtings done in 2010 in Iow nd Illinois nd in 2011 only in Illinois. IA, Iow; nd IL, Illinois. Stroilurin fungicide used ws Hedline (pyrclostroin), BASF, Reserch Tringle Prk, NC. Tretments were: UTC, n untreted control; VT/R1, single ppliction of stroilurin fungicide pplied t nthesis; R2/R3, single ppliction pplied t lister/milk growth stge; nd T, single ppliction pplied sed on threshold folir disese severity defined s 5% disese severity on the third lef elow the er lef or ove on 50% of the plnts in the plot. Fig. 3. Effect of fungicide on gry lef spot (GLS) nd northern corn lef light (NCLB) disese severity (%) ssessed t the R4/R5 crop developmentl stge, on the er lef of four mize hyrids grown t four sites etween 2010 nd The tril ws repeted in 2011 in Illinois, Iow, nd Wisconsin nd 2012 in Ohio. Stroilurin fungicide used ws Hedline (pyrclostroin), BASF, Reserch Tringle Prk, NC. Tretments were s follows: UTC, n untreted control; VT, VT/R1, single ppliction of stroilurin fungicide pplied t nthesis; R2, R2/R3, single ppliction pplied t lister/milk growth stge; nd T, single ppliction pplied sed on threshold folir disese severity defined s 5% disese severity on the third lef elow the er lef or ove on 50% of the plnts in the plot. IL, Illinois; IA, Iow; OH, Ohio; nd WI, Wisconsin. Wisconsin 2011 hd no threshold fungicide ppliction PHYTOPATHOLOGY

8 under low disese (Pul et l. 2011), nd it hs een postulted tht this is ecuse fungicides mnge minor folir diseses, sprophytic fungi, nd dely senescence (Bertelsen et l. 2001; Köehle et l. 2002). Nonetheless, cross our trils, lck of consistent yield increse in the sence of disese ws not oserved. These results concur with those of Brdley nd Ames (2010) who reported vriility in yield response of field trils conducted cross yers. Although Pul et l. (2011) oserved incresed men yield response t low levels of disese, it ws not lwys economiclly eneficil. TABLE 5. Effect of hyrid on stlk rot disese of corn (0 to 5 scle) ssessed t the R6 physiologicl mturity crop developmentl stge, on the stlks of four mize hyrids grown t four sites etween 2010 nd 2012 Hyrid IA IL IL P35F P33W P0461XR P0891XR LSD NS NS 0.29 P vlue Results re presented for stlk rot rtings done in 2010 in Iow nd Illinois nd in 2011 only in Illinois. IA, Iow; IL, Illinois; OH, Ohio; nd WI, Wisconsin. All hyrids were from DuPont-Pioneer Hi-red Interntionl Inc. P35F44, susceptile to GLS nd resistnt to northern corn lef light (NCLB); P33W84, resistnt to GLS nd susceptile to NCLB; P0461XR, susceptile to oth gry lef spot (GLS) nd NCLB; nd P0891XR, resistnt to oth GLS nd NCLB. Our trils were inoculted t two growth stges, with different comintions of S. turcic nd C. zee-mydis to enhnce disese development in the trils. The effect of inocultion on yield ws significnt in three out of eight site-yers (Illinois 2010 nd 2011 P < ; Iow 2010 P = ) ut more inocultions did not lwys result in more disese nd/or reduced yields. The presence of pthogen lone does not led to disese, since the host needs to e susceptile nd the previling wether conditions must e fvorle for the disese to occur (Stck 1999). Since disese in six out of eight site-yers ws low, the disese tringle conditions leding to incresed infection must not hve een met. At Wisconsin in 2010 where high yields were oserved, the period from July to August hd ove norml (30-yer verge) rinfll, corresponding to when mize ws t R3 to R4 crop developmentl growth stge or eginning grin fill. Genotype y environment interctions could hve contriuted to the high yields oserved. Resistnce in hyrid genetics nd culturl methods tht ffect the cropping environment should e considered s prt of n IPM system in ssocition with folir fungicide pplictions. The gol should e positive nd sustinle yield response under different environments nd depending on wht the risk fctors re on cse y cse sis. When continuously used in the sence of need, QoIcontining fungicides re cost tht my reduce producers profits nd increse risk of fungicide resistnce development (Blndino et l. 2012; Brdley nd Pedersen 2011; Wlker et l. 2009). Previous studies ssocite folir disese development with erly onset of senescence, incresed risk of stlk rot, reduced grin fill, nd consequently lower yields (Stck 1999; Roeth nd Elmore 2000). Furthermore, plnts with stlk rot re more susceptile to lodging, which cn slow down mchine hrvesting nd cn result in Fig. 4. Effect of fungicide on yield in kilogrms per hectre t four sites ssessed t time of hrvest fter physiologicl mturity etween 2010 nd The tril ws repeted in 2011 in Illinois, Iow, nd Wisconsin nd 2012 in Ohio. Stroilurin fungicide used ws Hedline (pyrclostroin), BASF, Reserch Tringle Prk, NC. Tretments were s follows: UTC, n untreted control; VT, VT/R1, single ppliction of stroilurin fungicide pplied t nthesis; R2, R2/R3, single ppliction pplied t lister/milk growth stge; nd T, single ppliction pplied sed on threshold folir disese severity defined s 5% disese severity on the third lef elow the er lef or ove on 50% of the plnts in the plot. IL, Illinois; IA, Iow; OH, Ohio; nd WI, Wisconsin. Wisconsin 2011 hd no threshold fungicide ppliction. Vol. 105, No. 8,

9 dropped ers during hrvest (Dodd 1980). In the present study, folir disese severity rnged from low to moderte, while stlk rot ws mrginl; the impct of oth diseses on yield ws generlly low. Our dt suggest tht fungicide ppliction cn e vile IPM component for hyrid mize production in the U.S. Corn Belt, provided ll sides of the disese tringle re met. However, yield dvntges s result of reduced disese or other fctors tht my e induced y QoI fungicide ppliction, especilly when disese is low or sent, were not consistent. More reserch is needed to define the disese threshold level for fungicide ppliction on hyrids, prticulrly in light of environmentl conditions nd hyrid genetics. Successful mngement of corn folir diseses should include prctices incorporting ll four components. These consist of prevention prctices such s plnting of hyrids with resistnce to disese, voidnce prctices such s rottion, monitoring prctices such s scouting, nd suppression prctices such s use of pesticides. ACKNOWLEDGMENTS This reserch ws supported y funds from USDA-NIFA-RAMP grnt, project numer , entitled, Sustinle Disese Mngement on Field Corn in the U.S. Corn Belt. We lso thnk DuPont- Pioneer who provided seed for the project. Isoltes of either C. zee-mydis or S. turcic were otined for Wisconsin USDA permit numers P526P nd P526P (C. zee-mydis) nd P526P (S. turcic). We lso gretly pprecite ll of the efforts of memers of ech lortory for their help in coordinting trils nd collecting dt used in these studies. Fig. 5. Effect of hyrid on yield in kilogrms per hectre t four sites ssessed t time of hrvest fter physiologicl mturity of four mize hyrids grown etween 2010 nd Tril ws repeted in 2011 in Iow, Illinois, nd Wisconsin nd 2012 in Ohio. All hyrids were from DuPont-Pioneer Hi-Bred Interntionl, Inc. P35, P35F44, susceptile to gry lef spot (GLS) nd resistnt to northern corn lef light (NCLB), P33, P33W84, resistnt to GLS nd susceptile to NCLB, P04, P0461XR, susceptile to oth GLS nd NCLB, nd P08, P0891XR, resistnt to oth GLS nd NCLB. IA, Iow; IL, Illinois; OH, Ohio; WI, Wisconsin. Ohio 2012, only two hyrids were evluted, P0461XR nd P0891XR. TABLE 6. P vlues summrizing ll fixed effect fctors relted to yield in kilogrms per hectre t four sites etween 2010 nd /2012 Fctors IA IL OH WI IA IL OH c WI d Hyrid Fungicide < H F Inocultion < < H I F I H F I The tril ws repeted in 2011 in Iow, Illinois, nd Wisconsin nd 2012 in Ohio. IA, Iow; IL, Illinois; OH, Ohio; nd WI, Wisconsin. Min effects nd their interctions: H, hyrid, F, fungicide; nd I, inocultion. c Ohio 2012, only two hyrids were evluted P0461XR nd P0891XR. d Wisconsin 2011, no threshold fungicide ppliction PHYTOPATHOLOGY

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