Confirmation by fluorescent tracer of coverage of onion leaves for control of onion thrips using selected nozzles, surfactants and spray volumes

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1 RTICLE IN PRESS Crop Protection 26 (27) Confirmtion y fluorescent trcer of coverge of onion leves for control of onion thrips using selected nozzles, surfctnts nd spry volumes Jennifer K. McIntyre-llen,, Jeff H. Tolmn, Cynthi D. Scott-Dupree, C. Ron Hrris Deprtment of Environmentl Biology, University of Guelph, Guelph, Ont., Cnd N1G 2W1 griculture nd gri-food Cnd, Southern Crop Protection nd Food Reserch Centre, 1391 Sndford Street, London, Ont., Cnd N5V 4T3 Received 16 ugust 26; received in revised form 2 Ferury 27; ccepted 2 Ferury 27 strct Trck spryer nd field spryer trils were completed to ssess the effect of different nozzles, surfctnts nd crrier volumes on product delivery to the inner leves of onion plnts using fluorescent trcer. Trck spryer trils reveled more trcer on the inner leves of onions using either the TeeJet s XR84 flt fn or D4/DC25 disc-core hollow cone nozzles. In three of four experiments, more trcer ws detected on onions spryed lone or comined with Sylgrd s 39 t 2 L/h thn plnts spryed with trcer+compnion s. When the crrier volume ws incresed to 4 L/h, more trcer ws detected on onions spryed lone or comined with Compnion. In field trils, the XR84 delivered more trcer thn the D4/DC25 (F ¼ 32.8; Po.; d.f. ¼ 1,77). The est coverge ws oserved on plnts spryed with the flt fn comined with grl s 9, spryed t either 4 L/h (29% coverge) or 6 L/h (23% coverge). r 27 Elsevier Ltd. ll rights reserved. Keywords: Fluorescent trcer; Onion thrips; Pest control; s; Surfctnts 1. Introduction Onion thrips, Thrips tci Lindemn, re economic pests of llium spp. worldwide (Horsfll nd Fenton, 1922; Boyce nd Miller, 1954; Theunissen nd Legutowsk, 1991; Brewster, 1994). dult nd immture onion thrips feed y piercing nd rsping lef tissues, removing the cell contents nd destroying chlorophyll-rich lef mesophyll (Molenr, 1984). The feeding dmge is chrcterized y white or silvery lesions nd cn result in reduced yield nd incresed susceptiility to infection y plnt pthogens (Howrd et l., 1994; Mckenzie et l., 1993). Onion thrips nymphs, the predominnt lifestge throughout the Ontrio growing seson (McIntyre-llen, 24), congregte deep within the xils of onion leves nd re thus well protected from folir-pplied chemicl Corresponding uthor. Ontrio Ministry of griculture, Food nd Rurl ffirs, 1 Stone Rod, Guelph, Ont., Cnd N1G 4Y2. Tel.: ; fx: E-mil ddress: jennifer.llen@ontrio.c (J.K. McIntyre-llen). control gents. This ehviour, coupled with the potentilly rpid increse of field popultions under fvourle conditions, continues to frustrte growers ttempting to control this pest round the world (Sites et l., 1992; Lewis, 1997; Muri, 2). In Ontrio, folir pplictions of one of the five registered insecticides re recommended for onion thrips control (OMFR, 26). Three of the five products, deltmethrin, lmd-cyhlothrin nd cypermethrin, re pyrethroids while the remining two products, dizinon nd dirom, re orgnophosphorus insecticides. Depending on the seson, growers pply 2 1 sprys to mnge onion thrips in crrier volumes rnging from 2 to 4 L/h. In Cnd, the Pest Control Products ct requires pesticide surfctnt comintions e registered for inclusion on product lels. Currently, products registered for use on onions for onion thrips control does not include surfctnt registrtions. Pesticide performnce is sed on prticulr insect, prticulr host, nd prticulr chemicl. Under lortory conditions, n insecticide my e pplied nd control /$ - see front mtter r 27 Elsevier Ltd. ll rights reserved. doi:1.116/j.cropro

2 1626 RTICLE IN PRESS J.K. McIntyre-llen et l. / Crop Protection 26 (27) evluted, often without considertion of the insect plnt interction. While Crosy (1973) estimted tht only 1% of insecticide reches the intended trget under field conditions, work y Hll nd dms (199) suggests tht even less thn 1% of insecticide reches the trget. The insect plnt interction must therefore e considered efore n insecticide ppliction is mde to mximize delivery nd susequent performnce of the control gent. To mximize delivery to the pest, growers should use equipment est-suited for the intended pest nd crop. n investigtion to optimize spry ppliction systems to improve efficcy of control gents for onion thrips y mximizing delivery into the onion lef xil ws therefore initited. There re mny types of spry nozzles ville, ech with chrcteristic spry ngle, droplet size, or spry pttern. Three different components of typicl spry delivery system were investigted: (1) spry nozzle, (2) surfctnt, nd (3) crrier volume. 2. Mterils nd methods 2.1. Trck spryer trils ll trils were conducted on onion plnts grown from set onion uls plnted in fire trys (27 cm 16.5 cm 8.5 cm deep) (Kord Products Ltd., Brmle, Ont.) filled with Premier ProMix BX growing medium (Premier Horticulture, Dorvl, Que.). Ech fire try ws plnted with pproximtely 22 onion uls in 2 2 rows with 2.5 cm spcings etween uls. Onions were mintined in greenhouse t the Southern Crop Protection nd Food Reserch Centre griculture nd gri-food Cnd in Delhi, Ontrio. Trys of onions were trnsported to the University of Guelph when onions reched height of 2 25 cm nd hd produced pproximtely 4 5 leves. s delivering different spry ngles, droplet sizes nd ptterns were evluted t severl ppliction pressures in 22 (four nozzles) nd 23 (three nozzles) (Tle 1). Tinopl CBS-X (Ci-Geigy, Greensoro, NC) (trcer), wter-solule fluorescent trcer dye, ws used to visulize spry depositions. In ll trils, the trcer ws pplied t concentrtion of 15 mg/l in reverse osmosis (RO) wter. Tinopl fluoresces rillint lue-violet (Stnilnd, 1958) with n sorption mximum of 349 nm nd n emission mximum of 44 nm is commonly used in spry deposition studies (Downer et l., 1997; Brer nd Prkin, 23; Brer et l., 23). Onion plnts were spryed with one of the following trcer+surfctnt tretments: trcer, trcer+sylgrd 39 [(.375%, v/v) (siloxylted polyether) (Dow Corning Corp., Midlnd, MI)] or trcer+compnion [(.2%, v/v) (octylphenoxy polyethoxy-9-ether) (Dow grosciences, Clgry, lt.)] using motorized trck spryer (Reserch Instrument Co., Guelph, Ont.). In ll experiments, the motorized trck spryer ws equipped with single nozzle. Between experiments, equipment ws clened nd the Tle 1 type, crrier volume nd surfctnt comintions tested type Crrier volume (L/h) Surfctnts tested Trck spryer trils 22 XR83 extended rnge flt 2 Sylgrd s 39, Compnion s XR84 extended rnge flt 2 Sylgrd 39, Compnion TJ6-84 vs twinjet 2 Sylgrd 39, Compnion D4/DC25 disc-core type cone 2 Sylgrd 39, Compnion 23 XR84 extended rnge flt 4 Sylgrd 39, Compnion TJ6-84 vs twinjet 4 Sylgrd 39, Compnion D4/DC25 disc-core hollow cone 4 Sylgrd 39, Compnion Field spryer trils 23 XR84 extended rnge flt 4, 6 Sylgrd 39, grl 9 s, LI-7 s D4/DC25 disc-core hollow cone 4, 6 Sylgrd 39, grl 9, LI-7 Sprying Systems Co., Wheton, IL, US. nozzle chnged. In experiments 1 4, four different TeeJet nozzles were tested: XR83 flt fn, XR84 flt fn, TJ6-84 twin jet nd D4/DC25 hollow cone. In experiments 5 nd 6, three different nozzles were evluted: XR84, TJ6-84 nd D4/DC25. For ll spry runs, ech nozzle ws clirted to deliver either 2 L/h (one pss) t 276 kp (experiments 1 3) or 4 L/h (two psses) t 276 kp (experiments 4 6). For ech experiment, the spry nozzle ws positioned 35 cm ove the plnt cnopy nd the spryer speed ws 1.15 km/h. Ech replicte of given tretment ws spryed during seprte pss of the trck spryer. Treted onions plnts were llowed to dry in the drk for 2 h. To compre droplet deposition, onion plnts were returned to the lortory nd eight onion plnts were hrvested from ech of three replictes for ech trcer+ surfctnt comintion. The outer leves were removed leving only the two inner leves for ech plnt. Using individul rzor ldes, the two inner leves were sectioned into three or four 2 cm regions (Fig. 1). Region 1 encompssed the lef re closest to the growing point, the loction where the mjority of nymphs re found throughout the growing seson. Using forceps, the two leves for ech cut region of ech plnt were trnsferred into lelled 2-mL glss scintilltion vil (Fisher Scientific, Unionville, Ont.) contining 2 ml of RO wter. The onion segments in ech vil were swirled for 3 s, removed with clen forceps nd discrded. Vils were

3 RTICLE IN PRESS J.K. McIntyre-llen et l. / Crop Protection 26 (27) Southern Crop Protection nd Food Reserch Centre griculture nd gri-food Cnd in London, filled with insecticide-residue-free orgnic soil on 9 My 23. Within ech microplot, onion seeds were spced 2 cm prt within row nd 3 cm etween rows. Trcer plus one of the following three surfctnts [Sylgrd 39 (.375%, v/v), grl 9 (nonylphenoxy polyethoxyethnol) (.2%, v/v) (Norc Concepts Inc., Ottw, Ont.) or LI-7 (.5%, v/v) (phosphtidylcholine methylcetic cid lkyl polyoxyethylene) (Lovelnd Industries, Greely, CO)], pplied in one of two crrier volumes (4 L/h or 6 L/h) using one of two nozzles (TeeJet XR84 flt fn or TeeJet D4/DC25 disc-core) were tested. ll tretments were replicted twice in rndomized complete lock design. On 14 ugust 23, ech trcer+surfctnt comintion ws pplied t 276 kp to onion plnts (eight-lef stge) using hnd-held, CO 2 pressurized R&D field-plot spryer (R&D Spryers, Opelouss, L) fitted with either single XR84 flt fn or D4/DC25 disc-core nozzle. The nozzle ws positioned pproximtely 3 cm ove the plnt cnopy. Two hours fter ppliction, six plnts from ech plot were crefully pulled, plced in individul lelled oxes, nd returned to the lortory. The inner three leves of ech plnt were exmined under n UVL-18 ultrviolet lmp (VWR Cnl, Toronto, Ont.) nd the totl mount of visile Tinopl ws estimted using plnt pthogen percent rting system for cerels (nonymous, 1975) Dt nlysis Fig. 1. Onion plnt schemtic demonstrting lef regions selected for study in trck spryer trils. cpped, plced into crdord oxes, covered with luminum foil nd stored t 4 1C for further nlysis. For ech experiment, control vils were lso prepred using onions spryed with RO wter only. Smples of 2 ml were pipetted from ech vil into well of 96-well microtitre plte (Dimed L Supplies, Mississug, Ont.). The concentrtion of trcer for ech tretment ws mesured fluorimetriclly with MFX Microtitre TM Plte Fluorometer (Dynex Technologies, Virgini, US) in conjunction with Dynex Reveltion 4.2 softwre (Dynex, 1999[h1]). Bckground fluorescence of control onions spryed with RO wter ws determined nd sutrcted from ll tretments Field spryer tril Dry yellow seed cooking onion seed (cv. Prince) ws hnd plnted (135 seeds/row) in three-row microplots (2.25 m long.9 m wide) (Hrris et l., 1971) t the Spry deposition on selected onion smples ws nlysed s fctoril nlysis of vrince (NOV) with three fctors: nozzle, surfctnt nd onion lef region in Trck Spryer Trils or with nozzle, surfctnt nd crrier volume in Field Spryer Trils (Sttistix 2.2, Tllhssee, FL). Mens were seprted using Fisher s protected lest significnt difference (LSD) test. 3. Results 3.1. Trck spryer trils In experiment 1, significntly more trcer ws deposited onto onion leves y the XR84 or D4/DC25 nozzles thn either XR83 or TJ6 84 nozzles (Tle 2). Significntly more trcer ws recorded on onion leves spryed with Sylgrd thn ny other trcer+surfctnt comintion. The highest mount of trcer ws recorded in Region 2, which received 39.6% of the totl trcer recorded. Further nlysis reveled significnt interctions mong nozzles, surfctnts nd regions (F ¼ 3.99; P ¼.1; d.f. ¼ 18,96). Two tretment comintions delivered significntly more trcer thn ll other comintions tested. One comintion, the XR84 nozzle nd trcer+sylgrd, resulted in FSU/onion (fluorescent units/onion) on Region 3. The second comintion of the D4/DC25 nozzle nd trcer+sylgrd resulted in

4 1628 RTICLE IN PRESS J.K. McIntyre-llen et l. / Crop Protection 26 (27) Tle 2 Reltive effectiveness of comintions of nozzle type nd surfctnts for deposition of Tinopl CBS-X, sed on men fluorescence units (FSU), on vrious regions of onion leves (see Fig. 1) pplied in trck spryer Prmeters Men (FSU/onion)7SEM Sttistics TeeJet s XR83 TeeJet s XR84 TeeJet s D4/DC25 TeeJet s TJ6 84 Region 1 Region 2 Region 3 Region 4 Sylgrd s 39 Compnion s No surfctnt () Experiment F ¼ 6.18; P ¼.1; d.f. ¼ 3,96 Region F ¼ 3.13; P ¼.2; d.f. ¼ 3,96 Surfctnt F ¼ 6.61; P ¼.1; d.f. ¼ 2,96 () Experiment F ¼ 3.78; P ¼.1; d.f. ¼ 3,72 Region F ¼ 19.15; P ¼.1; d.f. ¼ 2,72 Surfctnt F ¼ 4.24; P ¼.1; d.f. ¼ 2,72 (c) Experiment F ¼ 8.12; P ¼.1; d.f. ¼ 3,72 Region F ¼ 22.3; P ¼.1; d.f. ¼ 2,72 Surfctnt F ¼ 9.3; P ¼.1; d.f. ¼ 2,72 (d) Experiment F ¼ 4.53; P ¼.1; d.f. ¼ 3,72 Region F ¼ 65.12; P ¼.1; d.f. ¼ 2,72 Surfctnt F ¼ 3.17; P ¼.4; d.f. ¼ 2,72 (e) Experiment F ¼ 5.6; P ¼.1; d.f. ¼ 2,18 Region c F ¼ 1.5; P ¼.1; d.f. ¼ 3,18 Surfctnt F ¼ ; P ¼.1; d.f. ¼ 2,18 (f) Experiment F ¼ 2.81; P ¼.6; d.f. ¼ 2,18 Region F ¼ 6.26; P ¼.1; d.f. ¼ 3,18 Surfctnt F ¼ 15.9; P ¼.1; d.f. ¼ 2,18, not evluted. Mens within row followed y the sme letters re not significntly different s indicted y NOV nd Fisher s protected LSD (Po.5) FSU/onion on Region 2. While oserved differences in trcer recovery in Region 1, frequently the refuge for immture OT, were not sttisticlly significnt, more trcer tended to e recovered when pplied in comintion with Sylgrd or Compnion using the XR flt nozzles thn when pplied using either D4/DC25 or TJ6 84 nozzles (Fig. 2). In experiment 2, the D4/DC25 disc-core nozzle deposited significntly more trcer onto spryed onions thn ny of the other nozzles tested (Tle 2). Significntly less trcer ws recorded on onion leves when Sylgrd ws pplied. The highest mount of trcer ws recorded in Region 1 (65.5%), significntly more thn Region 2 (18.8%) or Region 3 (15.7%). significnt interction mong nozzles, surfctnts nd regions ws not oserved (F ¼.79; P ¼.66; d.f. ¼ 12,72). In Region 1, when trcer+compnion ws pplied y either the XR84 or TJ6 84 nozzle, significntly less trcer ws detected thn on leves spryed with the XR83 or D4/DC25 nozzles (Fig. 2). In experiment 3, the XR84 flt fn nozzle deposited significntly more trcer onto spryed onions thn ny of the other nozzles tested (Tle 2c). Significntly more trcer ws recorded on onion leves when Sylgrd ws dded to the spry mixture. The highest mount of trcer ws recorded in Region 1. Further nlysis reveled significnt interction mong nozzles nd surfctnts (F ¼ 3.62; P ¼.; d.f. ¼ 6,72). The XR84 nozzle comined with Sylgrd resulted in significntly more trcer (117.9 FSU) thn ny other comintion. comprison of spry deposition mong nozzles in Region 1 reveled tht lthough not sttisticlly different, more trcer ws deposited when trcer+sylgrd were pplied using either XR84 or D4/DC 25 nozzles (Fig. 2c). Conversely, significntly less trcer ws detected in Region 1 when onions were spryed with trcer+compnion y the XR83, XR84 or TJ6 84 nozzles. In experiment 4, significntly more trcer ws deposited onto onion leves y XR84, D4/DC25 nd TJ6 84 nozzles thn the XR83 nozzle (Tle 2d). Significntly more trcer ws recorded on leves when Sylgrd or no surfctnt were dded to the spry mixture. The highest mount of trcer ws recorded on Region 1 of the onion leves. significnt interction existed mong nozzles, surfctnts nd regions on this spry dte (F ¼ 9.11;

5 RTICLE IN PRESS J.K. McIntyre-llen et l. / Crop Protection 26 (27) FSU per onion FSU per onion FSU per onion Trcer + Sylgrd Trcer + Compnion Trcer lone Trcer + Sylgrd Trcer + Compnion Trcer lone B B XR83 XR84 D4/DC25 TJ6 84 XR83 XR84 D4/DC25 TJ6 84 Trcer + Sylgrd Trcer + Compnion Trcer lone Trcer + Sylgrd Trcer + Compnion Trcer lone B XR83 XR84 D4/DC25 TJ6 84 FSU per onion FSU per onion FSU per onion Trcer + Sylgrd Trcer + Compnion Trcer lone Trcer + Sylgrd Trcer + Compnion Trcer lone B XR84 D4/DC25 TJ6 84 B B XR83 XR84 D4/DC25 TJ6 84 XR84 D4/DC25 TJ6 84 B C Fig. 2. Spry deposition, s mesured y fluorescence units (FSU), of Tinopl CBS-X mixed with surfctnts on Region 1 of onion leves pplied in 2 L/h (,, c) or 4 L/h (d, e, f) t 276 kp in trck spryer. For ech experiment, comprison of ech surfctnt cross nozzle type ws determined y NOV nd Fisher s protected LSD test; columns followed y the sme letters (either cpitlized or itlicized) re not significntly different (Po.5). P ¼.1; d.f. ¼ 12,72). Two tretment comintions delivered significntly more trcer thn ll other comintions tested. The TJ6-84 nozzle comined with Sylgrd nd the D4/DC25 nozzle with no surfctnt delivered nd FSU, respectively, to Region 1. The next est tretment ws the XR84 nozzle comined with Sylgrd (311.6 FSU) (Fig. 2d). In experiments 5 nd 6, the crrier volume ws incresed from 2 to 4 L/h. Regrdless of experimentl dte, onion plnts spryed with Compnion or no surfctnt hd significntly more trcer thn onion plnts spryed with Sylgrd nd trcer mixture (Tle 2e,f). In experiment 5, onion plnts spryed with Sylgrd retined 2.9% of the totl trcer recorded, which ws significntly less thn plnts spryed with Compnion (48.5%) or no surfctnt (48.6%). In experiment 6, onion plnts spryed with Sylgrd retined only 3.4% of the totl trcer recorded, significntly less thn plnts spryed with Compnion (51.3%) or no surfctnt (45.2%). In experiment 5, more trcer ws recorded in Region 1 thn ny other region while in experiment 6, Regions 1 3 were not significntly different from ech other. Further nlysis reveled significnt interction mong nozzles, surfctnts nd regions in oth experiments (experiment 5: F ¼ 3.97; P ¼.; d.f. ¼ 12,18), (experiment 6: F ¼ 3.16; P ¼.1; d.f. ¼ 12,18). In experiment 5, significntly more trcer ws detected in the sence of either surfctnt on onions spryed with the TJ6 84 (Region 1, FSU), XR84 (Region 2, FSU) or D4/DC25 (Region 2, FSU) nozzles. Comprison of trcer deposition mong nozzles reveled more trcer ws detected in Region 1 when pplied y XR84 or TJ6 84 in the sence of surfctnt (Fig. 2e). In experiment 6, significntly more trcer ws detected in ll three regions of onion plnts spryed with the XR84 in the sence of surfctnt (Region 1, FSU; Region 2, FSU; Region 3, 27 FSU) nd TJ6 84 nozzles in the sence of surfctnt (Region 1, FSU) or when comined with Compnion (Region 2, FSU; Region 3, 287 FSU). Significntly more trcer ws lso detected in Region 2 of onion plnts spryed with the D4/DC25 nozzle in the sence of surfctnt (256.3 FSU) or when comined with Compnion (239.5 FSU). Similr to the results oserved in experiment 5, significntly more trcer ws detected in Region 1 when pplied with XR84 or TJ6 84 in the sence of surfctnt (Fig. 2f).

6 163 RTICLE IN PRESS J.K. McIntyre-llen et l. / Crop Protection 26 (27) Field spryer tril Due to the inconsistent nd/or poor performnce of Compnion, especilly when compred to tretments receiving no surfctnt in the trck spryer trils, two different non-ionic surfctnts, grl 9 nd LI7, were tested long with Sylgrd in the field. Significntly more trcer ws detected on the inner leves of onion plnts spryed with the XR84 nozzle thn on leves spryed with the D4/DC25 disc-core nozzle (F ¼ 32.77; P ¼.1; d.f. ¼ 1,77) (Tle 3). In ddition, significnt difference ws oserved mong surfctnts (F ¼ 19.95; P ¼.1; d.f. ¼ 3,77) nd etween crrier volumes (F ¼ 5.83; P ¼.1; d.f. ¼ 1,77). significnt interction etween nozzles, surfctnts nd volumes ws lso oserved (F ¼ 3.28; P ¼.2; d.f. ¼ 3,77). The est nozzle, surfctnt, crrier volume comintion ws the XR84 nozzle comined with grl 9 t oth 4 nd 6 L/h; which respectively covered 29% nd 23% of treted inner leves (Fig. 3). The next est comintion, Tle 3 Effectiveness of comintion tretments of nozzles (1, TeeJet s XR84; 2, TeeJet s D4/DC25 disc core), surfctnts (1, no surfctnt; 2, Sylgrd s 39; 3, LI-7 s ; 4, grl s 9) nd crrier volumes (1, 4 L/h; 2, 6 L/h ) for men percent coverge of Tinopl CBS-X onto onion leves, pplied y R&D field plot spryer Prmeter Men % coverge7sem Surfctnt c c Volume surfctnt volume Surfctnt Volume Men % coverge defgh def fgh cd cde c h efgh h gh defgh defg efgh de Mens within row followed y the sme letters re not significntly different s indicted y NOV nd Fisher s protected LSD (Po.5). Mens within the column followed y the sme letters re not significntly different s indicted y NOV nd Fisher s protected LSD (Po.5). No surfctnt Sylgrd 39 LI-7 grl 9 No surfctnt Sylgrd 39 LI-7 grl 9 % Coverge % Coverge c c 5 c c 6 L/h 4 L/h 6 L/h 4 L/h Volume Volume Fig. 3. Percent coverge of the trcer, Tinopl CBS-X, mixed with surfctnts on onion leves in two crrier volumes t 276 kp pplied using n R&D field plot spryer. Within crrier volume for given nozzle, columns followed y the sme letters re not significntly different (Po.5) s determined y NOV nd Fisher s protected LSD.

7 RTICLE IN PRESS J.K. McIntyre-llen et l. / Crop Protection 26 (27) XR84, LI-7 t 6 L/h, delivered 18% coverge. For the D4/DC25 disc-core nozzle, more trcer ws oserved t oth volumes when comined with either LI-7 or grl 9 (Fig. 3). However, the percent coverge of this nozzle ws mrkedly less thn tht oserved on onions spryed with the XR84 nozzle. 4. Discussion Onion thrips re thigmotctic, preferring to congregte deep within the xils of the youngest onion leves throughout the growing seson. This ehviour offers protection from predtors, from environmentl stresses nd possily from control gents. etter understnding of the interctions of insecticide ppliction nd insect ehviour cn enefit growers in their ttle to control onion thrips. Improved delivery of insecticides into the lef xils of onion plnts will improve control of onion thrips nd my reduce the overll numer of pesticide pplictions required. Trck spryer work demonstrted tht on smll onion plnts (4 5-lef stge), ppliction of crrier mixed with Sylgrd vi either n XR84 or D4/DC25 nozzle, delivered the most trcer into the lowest region of the inner leves when pplied in crrier volume of 2 L/h. When the crrier volume ws douled to 4 L/h, less trcer ws detected when mixed with Sylgrd regrdless of the nozzle tested. Sylgrd is n orgno-silicone surfctnt. Studies hve shown tht non-ionic surfctnts cn lower the surfce tension of spry solution to mn/m; the ddition of silicone component cn further lower the surfce tension to 22 mn/m (Penner, 2). However, this very chrcteristic my led droplets to colesce nd susequently run off the plnt (Petroff, 23). Therefore, it is possile tht during the second trck spryer pss, required to deliver the higher volume, there ws greter tendency for the trcer+sylgrd comintion to run off treted onion plnts. Bsed on these findings, growers my e le to increse effectiveness of folir sprys for onion thrips control on young onion plnts y dding Sylgrd rther thn incresing crrier volume. However, the lck of consistency mong experiments 1 4 is importnt to note. Bsed on these results, it is difficult to mke ny firm recommendtions sed on trck spryer results lone. In Cnd, eight non-ionic surfctnts, flling into one of six different chemicl composition ctegories, re registered for griculturl uses. In the trck spryer trils, two types of non-ionic surfctnts were studied, n octylphenoxy-polyethoxy-9-ethnol (Compnion) nd silicone polyether (Sylgrd). Following the poor results following the ppliction of Compnion, the uthors decided to evlute non-ionic surfctnts from two different chemicl composition ctegories, grl 9 (nonylphenoxy polyethoxyethnol) nd LI7 (phosphtidycholine, methlcetic cid, lky polyoxyethylene ether) in ddition to Sylgrd in the field. lthough the trck spryer dt demonstrted tht ppliction of Sylgrd t higher crrier volume did not increse coverge, higher crrier volumes were evluted under field conditions for two resons. Firstly, field experiments were performed on lrge, older plnts with greter lef surfce re, therey requiring more wter for coverge. Secondly, in Ontrio, generl recommendtion in the wr ginst onion thrips is to increse crrier volumes. Therefore, it ws importnt to test different surfctnts t higher wter rtes under field conditions. In the field spryer tril, mture onion plnts (eight-lef stge) spryed with trcer+grl 9 vi the XR84 nozzle displyed the est coverge of the inner leves t oth crrier volumes tested. In fct, less trcer ws detected on the inner leves of plnts spryed with ny trcer+ surfctnt comintion using the D4/DC25 nozzle. Oserved differences etween the two nozzle types my e due to the droplet size or volume men dimeter (VMD). t 276 kp, the XR84 flt fn nozzle delivers droplets with VMD of pproximtely 33 mm (nonymous, 1993). Pulished dt report tht the D4/DC25 disc-core nozzle delivers droplets with VMD of 32 nd 275 t 167 nd 333 kp, respectively (nonymous, 1967). Bsed on the pressure used in these experiments (276 kp), the VMD of droplets delivered with D4/DC25 nozzle would hve een smller thn those delivered y XR84. In the trck spryer tril, the younger, smller onions were difficult trget to wet, nd the D4/DC25 disc-core nozzle my hve more successfully delivered spry droplets into the lef xils ecuse there were fewer leves nd more lef surfce ws contcted y the smller droplets. s well, drops produced y this nozzle type my hve provided greter overll coverge nd een more moile on younger, wxier leves. In the field tril, mture onion plnts (8 9-lef stge) hd tller, wider individul leves nd the inner leves were less ppressed compred to young plnts used in trck spryer trils. Therefore, movement of the smller droplets produced y the D4/DC25 nozzle my hve een slowed y environmentlly rded older leves or the droplets my hve dried on contct rther thn running down the insides of the inner leves. In ddition, plnts in the field tril my hve dried more quickly thn onion plnts spryed in trck spryer trils. Wether records tken t time of spry ppliction indicted tht the ir temperture nd reltive humidity were 29 1C nd 56%, respectively. By the time the plnts were hrvested, the temperture hd risen to 33 1C nd the reltive humidity hd fllen to pproximtely 5%. Temperture nd reltive humidity my lso help to explin why the ddition of Sylgrd, under field conditions, did not increse percent coverge in the inner leves, s oserved in trck spryer trils. Following ppliction in the field, plnts spryed with Sylgrd ppered wetter thn plnts spryed with other tretment comintions. In generl, orgnosilicone djuvnts (e.g. Sylgrd), re noted for their superior spreding ilities nd extremely low surfce tensions (Sun, 1996). Murphy et l. (1991) showed tht solutions contining

8 1632 RTICLE IN PRESS J.K. McIntyre-llen et l. / Crop Protection 26 (27) orgnosilicones drmticlly incresed the reltive spred re compred to conventionl djuvnts y reducing the contct ngle etween droplets nd the intended surfce. If the contct ngle is reduced too much, the spry droplet my either hve tendency to dry more quickly on contct or, in higher wter volumes, run off the contcted surfce. Considering the mient ir tempertures nd low reltive humidity t the time of ppliction nd hrvest, it is possile tht droplets dried quickly on contct nd did not run into the lef xil. It is lso possile tht with the incresed crrier volumes there ws more run off nd thus less trcer deposited on the onion leves. In the trck spryer trils, less trcer+sylgrd ws detected in Region 1, regrdless of nozzle, when the crrier volume ws incresed. ppliction of lower volume of crrier (e.g. 2 L/h) my hve resulted in retention of more trcer on the lef surfce. The ddition of surfctnts should help to lower the surfce tension llowing droplets to hit nd run, regrdless of nozzle type. This ws oserved when onion plnts were spryed using the D4/DC25 nozzle. The ddition of either LI-7 or grl 9 incresed the overll coverge of onion leves spryed from 2% to 3% t 4 L/h nd 9% to 12% t 6 L/h. In the sence of ny surfctnt, plnts spryed with the XR84 flt fn hd 14 greter coverge of the inner leves thn plnts spryed with D4/DC25 hollow cone t 4 L/h nd 2 greter coverge when pplied t 6 L/h. With the ddition of grl 9, ppliction using the XR84 nozzle resulted in 3% coverge t 4 L/h nd 23% coverge t 6 L/h. The gol of this work ws to oserve spry coverge ptterns of different nozzles, surfctnts nd crrier volumes on onion plnts in the hope of identifying comintion tht est delivered spry solution into the lef xils of onion plnts to etter trget onion thrips popultions. Bsed on the results of this work, choosing the right nozzle, surfctnt nd crrier volume is criticl. The wrong comintion of nozzle, surfctnt nd insecticide will cost the grower time nd money. When the insecticide is not delivered to the onion lef xils, onion thrips numers will not e reduced, popultions will continue to increse nd the grower will e forced to mke more spry pplictions in n ttempt to control the pest. With only two clsses of insecticides registered for control of onion thrips in Ontrio, when more sprys re needed, the development of insecticide resistnce ecomes vlid concern. Therefore, identifying the est comintion of nozzle, surfctnt nd crrier volume is importnt for oth economic nd environmentl resons. s mentioned erlier, this work demonstrted tht extrpoltions regrding spry ppliction from the lortory to the field re not lwys vlid. These lortory nd field trils did, however, emphsize the need for further reserch into vrious mechnicl prmeters ssocited with insecticide ppliction for mngement of cryptic pest such s onion thrips. 5. Conclusions Efficcious delivery of pest control gent to the loction of the pest orgnism is perhps the wekest link in the chin of events leding from identifiction of the pest nd selection of the control gent to stisfctory control of tht pest. This work demonstrted gret vrition in the mount of trcer detected in the trget tretment re depending on the nozzle, the presence nd type of surfctnt nd the crrier volume. Under field conditions, grl 9 delivered the est coverge regrdless of crrier volume or nozzle type. With tht sid, it is importnt tht growers exercise cre when choosing suitle surfctnt nd crrier volume for onion thrips control s certin surfctnt/crrier volume comintions did not dequtely deliver mterils to the trget site. It is thus dvisle to further investigte vrious prmeters ssocited with insecticide ppliction under field conditions to mximize control while minimizing the numer of insecticide pplictions. Bsed on this preliminry reserch, we recommend tht onion growers dd suitle surfctnt to registered insecticides nd pply using TeeJet s XR84 flt fn spry nozzles. cknowledgements The uthors would like to thnk lex Molnr of griculture nd gri-food Cnd for creting the onion plnt illustrtion. We grtefully cknowledge finncil support from Food Systems 22 OMFR, Ontrio Fruit nd Vegetle Growers ssocition, Thedford- Grnd Bend Vegetle ssocition nd griculture nd gri-food Cnd. References nonymous, XR TeeJet extended rnge flt spry tips volume medin dimeter versus pressure curves. Dt Sheet No Sprying Systems Co. nonymous, Cerel evlution. In: CIB-GEIGY Field Tril Mnul. ci-geigy, Bsle, Switzerlnd. nonymous, Spry prticle size versus orifice disc no. with vrious core sizes ses on sprying wter t 7 1F. Dt Sheet No Sprying Systems Co. Brer, J..S., Prkin, C.S., 23. Fluorescent trcer techniques for mesuring the quntity of pesticide deposited to soil following soil ppliction. Crop Prot. 22, Brer, J..S., Prkin, C.S., Chowdhury,.B.M.N.U., 23. Effect of ppliction method on control of powdery mildew (Blumeri grminis) on spring rley. Crop Prot. 22, Boyce, K.E., Miller, L.., Overwintering hitts of the onion thrips, Thrips tci Lind. (Thysnopter: Thripide) in southwestern Ontrio. Rep. Entomol. Soc. Ont. 84, Brewster, J.L., Onions nd Other Vegetle lliums. CB Interntionl, Oxon, UK, 236pp. Crosy, D.G., The fte of pesticides in the environment. nnu. Rev. Plnt Physiol. 24, Downer, R.., Kirchner, L.M., Hll, F.R., Bishop, B.L., Comprison of droplet spectr of fluorescent trcers commonly used to mesure pesticide deposition nd drift. In: Goss, G.R., Hopkinson,

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