New Zealand Jurnal f Crp and Hrticultural Science ISSN: 01140671 (Print) 11758783 (Online) Jurnal hmepage: http://www.tandfnline.cm/li/tnzc20 Effects f hydrgen cyanamide n budbreak and flwering in kiwifruit (Actinidia delicisa Hayward') H. G. Mcphersn, A. C. Richardsn, W. P. Snelgar & M. B. Currie T cite this article: H. G. Mcphersn, A. C. Richardsn, W. P. Snelgar & M. B. Currie (2001) Effects f hydrgen cyanamide n budbreak and flwering in kiwifruit (Actinidia delicisa Hayward'), New Zealand Jurnal f Crp and Hrticultural Science, 29:4, 277285, DOI: 10.1080/01140671.2001.9514189 T link t this article: https://di.rg/10.1080/01140671.2001.9514189 Published nline: 22 Mar 2010. Submit yur article t this jurnal Article views: 389 View related articles Citing articles: 18 View citing articles Full Terms & Cnditins f access and use can be fund at http://www.tandfnline.cm/actin/jurnalinfrmatin?jurnalcde=tnzc20
New Zealand Jurnal f Crp and Hrticultural Science, 2001, Vl. 29: 277285 00140671/01/29040277 $7.00 The Ryal Sciety f New Zealand 2001 277 Effects f hydrgen cyanamide n budbreak and flwering in kiwifruit (Actinidia delicisa 'Hayward') H. G. MCPHERSON The Hrticulture and Fd Research Institute f New Zealand Ltd Mt Albert Research Centre Private Bag 92 169 Auckland, New Zealand A. C. RICHARDSON The Hrticulture and Fd Research Institute f New Zealand Ltd Kerikeri Research Centre P. O. Bx 23 Kerikeri, New Zealand email: arichardsn@hrtresearch.c.nz W. P. SNELGAR M. B. CURRIE The Hrticulture and Fd Research Institute f New Zealand Ltd Mt Albert Research Centre Private Bag 92 169 Auckland, New Zealand Abstract Effects f hydrgen cyanamide (HC) applicatin t kiwifruit (Actinidia delicisa (A. Chev.) C.F. Liang et A. R. Fergusn 'Hayward') vines were assessed ver fur seasns (199699) in three New Zealand kiwifruitgrwing areas. HC advanced the date f budbreak t c. 40 days after applicatin, despite the date f applicatin varying frm 33 t 92 days befre natural budbreak. Fr every day that HC advanced budbreak, there was a 0.5day advance in the date f flwering (r 2 = 0.92). The smaller advance in flwering resulted frm the cler temperatures experienced between budbreak and flwering in the treated vines. HC applicatins tended t reduce the spread f budbreak and flwering, with the greatest effect at the warmest sites. H01011 Received 19 March 2001; accepted 20 August 2001 Applicatin f HC usually increased budbreak and the ttal number f flwers at the warmest tw sites, but nly slightly reduced their seasnal variatin as this was largely the result f the amunt f winter chilling vines received. The number f flwers per winter bud prduced by untreated vines was reduced by 0.44 per 1 C. The percentage f ttal flwers that were lateral r side flwers was reduced by HC applicatin frm 14 t 4% at the warmest site and 29 t 19% at the clest site. Keywrds kiwifruit; Actinidia delicisa; hydrgen cyanamide; HiCane ; Drmex ; budbreak; flwering; phenlgy INTRODUCTION In warm grwing regins, the flwering f kiwifruit (Actinidia delicisa (A. Chev.) C.F. Liang et A. R. Fergusn 'Hayward') is ften limited by inadequate winter chilling (LinsleyNakes & Allan 1987). When hydrgen cyanamide (HC) is applied t drmant vines, the amunt f budbreak and flwering increases and it has been used t ffset the effects f pr winter chilling in a range f cuntries including: New Zealand (Henzell & Brisce 1986); Israel (Shulman et al. 1986); Australia (Paulin & McHattie 1989); Chile (Lckwd 1989); Suth Africa (LinsleyNakes 1989); Brazil (Shuck & Petri 1995); and Italy (Csta et al. 1997). Sme cnsider the applicatin f HC t be the management practice that currently has the greatest single effect n the prfitability f kiwifruit prductin in New Zealand. The rate f chemical applicatin can have a majr influence n the efficacy f HC. Richardsn et al. (1994) applied 1, 2, 3, 4, and 6% HC (active ingredient) in Kerikeri, the warmest prductin area f New Zealand, and fund budbreak increased prgressively with increasing cncentratin. The number f fruit prduced was greatest at cncentratins f 3 and 4% in the 2 f the 3 years that had the lwest natural chilling. In the third year rates f HC had little effect n yield. The ttal
278 New Zealand Jurnal f Crp and Hrticultural Science, 2001, Vl. 29 number f flwers prduced by a winter bud was greatest with the 6% treatment fllwing the clest winter, and between 2 and 4% in the ther 2 years. Allen et al. (1997) in Suth Africa, fund that thugh 6% prmted higher ttal and reprductive budbreak in warmer rchards, 4% was best in cl rchards. Shuck & Petri (1995) used 0.5, 1, 2, and 3% HC in Brazil and fund the higher cncentratins gave the best budbreak but, in sme circumstances mre flwers per winter bud were btained with the lwer cncentratins. The time f applicatin f HC can als affect the amunt f budbreak. The highest budbreak was fund t ccur when HC was applied 45 weeks befre natural budbreak (Shuck & Petri 1995), 6 weeks befre natural budbreak (Henzell & Allisn 1993a), and 7 weeks befre natural budbreak (Allan et al. 1997). Reliable cmparisn f these results is difficult because the criteria used t define budbreak either vary, r are nt stated. Winter temperatures appear t alter the respnse f vines t HC. Richardsn et al. (1995) fund that the respnse f the vines t HC varied frm year t year and that the abslute numbers f flwers per winter bud were much higher in the year with the highest natural chilling. Csta et al. (1997) stated that the greater the number f chilling units at the time f HC applicatin, the greater was the advance in the date f budbreak. In a warm Suth African envirnment, there was a synergistic effect between the use f evaprative cling and HC t increase 'Hayward' fruit size (Allan et al. 1997). The purpse f this paper is t examine the impact f cntrasting climates and seasns n the efficacy f HC in 'Hayward' kiwifruit, with a view t imprving the understanding f its use. MATERIALS AND METHODS 'Hayward' kiwifruit vines were grwn n three HrtResearch Research Orchards cvering the gegraphical range f the principal New Zealand kiwifruitgrwing regins. The rchards were lcated near Kerikeri, Te Puke, and Riwaka. Measurements were made ver fur grwing seasns (1996/971999/2000). The year used t identify each set f data is the year in which budbreak and flwering ccurred (i.e., the 1996/97 grwing seasn was referred t as the 1996 seasn). All vines were mre than 10 years ld, trained n Tbar trellises, managed using standard cmmercial practices (Sale 1983), and grwing near the middle f blcks t minimise shading by the shelterbelts. At each site there were 10 plts f tw vines, with hydrgen HC randmly allcated t the same five plts each seasn and applied by spraying a vlume f 600 litre ha" 1 at a rate f 3.12 kg active ingredient per 100 litre (as 6.24% HiCane prduct). HC applicatin was targeted fr the first week in August, but applicatin was dependent n suitable weather cnditins and applicatin ccurred between 33 and 92 days befre natural budbreak. T reduce variability, tw typical (mdal) fruiting canes were chsen n each f the vines (ne cane per side) and these were used fr the assessment f budbreak and flwering. Canes were assessed twice weekly and the ttal number f buds which had reached budbreak were cunted frm the first signs f bud mvement nwards, t prvide frm 5 t 10 bservatins ver the perid f budbreak. Each emerging bud was said t have reached budbreak when it frmed a dme shape, fllwing the definitin f Brundell (1975). The final budbreak measurement was made when n mre buds were breaking. The time curse f budbreak was analysed using the ppulatin f buds n the 20 canes fr each treatment at each site. A cumulative nrmal curve was fitted by leastsquares t the cumulative cunt. The estimated mean time f budbreak crrespnds t the time f 50% ccurrence. The spread f budbreak was defined as 4 times the standard deviatin (SD) (i.e., tw SD either side f the mean) and this includes 95% f the ccurrences. The time curse f flwering was estimated in the same way, except that bservatins f the sample canes were dne 3 times per week and each flwer was designated as pen when the petals had pened sufficiently t permit easy access t bees. The prgress f develpment between budbreak and flwering can be expressed as the time between events (with units f days per event), r mre lgically as a rate (with units f events per day) as was dne in this case. Analysis f variance f data fr amunt f budbreak and flwering were based n individual vine means. In the case f the spread f budbreak and flwering, the cumulative nrmal curves were fitted fr each treatment in each year, cnsequently analysis f variance was nt cnducted n this. The experimental vines were grwing within 2 km and 10 m altitude f a standard meterlgical site. Daily maximum and minimum temperatures frm each site were used t calculate mean temperatures, rather than hurly temperatures, as daily temperatures are mre readily accessible t
McPhersn et al. Cyanamide effects n kiwifruit 279 cfl c 1I ^ (u CQ S ing 0) S" FT" ^ ring u; LL s 1 CC K8 K6 K9 atin n 13 14 13 12 K7 T8 ppli 11 O I E 10 T9 T6 T7 2 H 2 CD Q. h 8 16 Jul 5Aug 25Aug 14Sep 4 Oct Date 24 Oct 13Nv 3 Dec Fig. 1 Dates f: applicatin f hydrgen cyanamide (HC); budbreak f 'Hayward' kiwifruit (Actinidia delicisa) treated vines; budbreak f untreated vines (natural budbreak); flwering f treated vines; and flwering f untreated vines. Open circles indicate events n HCtreated vines and filled circles thse n untreated vines. These are shwn with respect t the mean air temperature f the perid frm applicatin f HC t natural budbreak. Vertical lines shw averages fr three f the events. Line fr temperature as a functin f the date f natural budbreak and flwering f the treated vines are shwn. Numbers indicate the last digit f the year f the result (i.e., Year 6 = spring f 1996) and the letters indicate the site (K = Kerikeri, T = Te Puke, R = Riwaka). thers wishing t use the crrelatin's develped here. Mean winter temperatures were calculated frm the daily mean temperatures fr the mnths f May, June, and July. RESULTS AND DISCUSSION Time f budbreak The date f the midpint f natural budbreak was later in warmer cnditins (Fig. 1, Table 1). The date f natural budbreak and mean winter temperature at each site averaged ver the 4 years was: 17 Octber fr Kerikeri (13.0 C); 24 September fr Te Puke (11. PC); and 21 September fr Riwaka (8.4 C) (a range f 24 days). McPhersn et al. (1994) reprted a similar trend. Hwever, cntrlled envirnment studies shwed that warm spring temperatures actually advanced budbreak when the vines had experienced a cmmn winter temperature regime (Warringtn & Stanley 1986). This implies that the later natural budbreak that ccurred in the warmer field envirnments was the because f the lw amunt f winter chilling at thse sites.
280 New Zealand Jurnal f Crp and Hrticultural Science, 2001, Vl. 29 The time between the applicatin f HC and budbreak f the treated vines averaged 40 days with nly minr variatin (SD = 3.6 days), despite the date f applicatin varying frm 33 t 92 days befre natural budbreak. The average date f HC applicatin was 5 August, with a range f 18 days ver the three sites and 4 years (Fig. 1). Variatin in the date f applicatin f HC ccurred because successful applicatin is weather dependent. In experiments ver 2 years in the nrtheast f Italy, and 4 years in the suth f Italy (Csta et al. 1997), the mean duratin frm applicatin f HC t budbreak f the treated vines was 30 days but highly variable (SD = 13 days). Hwever, Csta et al. (1997) did nt define their criteria fr budbreak, but Table 1 Mnthly temperatures averaged fr the winter perid f May, June, and July at three sites which represent the range f kiwifruitgrwing regins in New Zealand. Year 1996 1997 1998 1999 Mean Kerikeri 12.3 12.4 14.1 13.1 13.0 Mean winter temperature ( C) Te Puke 10.3 10.5 12.1 11.3 11.1 Riwaka 7.5 8.0 9.2 8.7 8.4 if they recrded the start f budbreak, rather than the 50% budbreak used in the present experiment, this culd accunt fr the 10day difference. Inglese et al. (1998) fund in suthern Italy that HC applied 68 weeks befre the expected time f budbreak, caused vines t begin budbreak 2025 days befre natural budbreak. Recmmendatins fr HC applicatin dates are ften expressed relative t the date f expected natural budbreak (Henzell & Allisn 1993a; Shuck & Petri 1995; Allan et al. 1997). Our results shw that this is nt warranted in the case f phenlgical develpment althugh it may be in relatin t ther variables. The date f budbreak ccurs c. 40 days frm applicatin and is nt related t the date f natural budbreak (Fig. 1). Spread f budbreak The spread f natural budbreak decreased with temperature frm an average f 47 days at Kerikeri (mean winter temperature f 13.0 C) t 21 days at Riwaka (mean winter temperature f 8.4 C) (Table 2). The rati f the spread f budbreak in treated t nntreated vines was 0.4 at the warmest site (Kerikeri), 0.8 at the intermediate site (Te Puke), and 1.0 at the clest site (Riwaka) if the unusual result in 1997 at Kerikeri is set aside. This pattern supprts the widely held belief that HC cmpresses budbreak and that the effect is the greatest where winter chilling is Table 2 Effect f hydrgen cyanamide (HC) n budbreak and flwering at three cntrasting sites ver 4 years. Mean values fr each site are fllwed by a standard errr in parentheses. Ratis f values fr HCtreated vines t the untreated vines are als given. Budbreak spread (days) Flwering spread (days) Site Year Untreated Treated with HC HC/ untreated Untreated Treated with HC HC/ untreated Kerikeri Te Puke Riwaka 1996 1997 1998 1999 Mean 1996 1997 1998 1999 Mean 1996 1997 1998 1999 Mean 52.7 35.2 57.8 42.4 47.0 (5.9) 17.5 34.1 30.9 26.1 27.2 (3.7) 16.5 24.3 22.0 21.2 21.0(1.9) 15.7 42.4 22.6 19.4 25.0 (6.9) 14.4 22.0 23.8 24.0 21.1(2.6) 20.2 18.2 12.6 27.4 19.6 (3.5) 0.30 1.21 0.39 0.46 0.59 0.82 0.65 0.77 0.92 0.79 1.23 0.75 0.57 1.29 0.96 19.0 13.2 35.8 29.8 24.5 (5.9) 8.9 9.3 23.6 18.6 15.1 (4.2) 11.2 9.5 15.2 12.6 12.1 (1.4) 5.4 6.5 7.7 8.1 6.9 (0.7) 8.9 8.5 8.4 9.9 8.9 (0.4) 8.8 4.7 8.7 17.0 9.8 (3.0) 0.28 0.50 0.22 0.27 0.32 1.00 0.91 0.36 0.53 0.70 0.78 0.50 0.57 1.35 0.80
McPhersn et al. Cyanamide effects n kiwifruit 281 Fig. 2 Advance in flwering f 'Hayward' kiwifruit {Actinidia delicisa) vines that accmpanied the advance in budbreak as a result f hydrgen cyanamide (HC) applicatin. Squares indicate results frm Kerikeri, circles thse frm Te Puke, and triangles results frm Riwaka. Remaining anntatin is explained in Fig. 1. D) 25 (U g 10 PK8 Q) 5 O < 0 y = 0.30 + 0.486 x {r2 = 0.92) 5 10 10 20 30 40 Advance in budbreak (days) 50 60 Fig. 3 Effect f the mean temperature fr the perid frm budbreak t flwering fr 'Hayward' kiwifruit {Actinidia delicisa) vines n the rate f develpment between budbreak and flwering. Slid line indicates the regressin fr the cntrl and vines treated with hydrgen cyanamide (HC) cmbined and the dashed line the regressin fr the untreated vines frm McPhersn et al. (1992). Anntatin is explained in Fig. 1. > CO 1 w O I 1 0.028 0.026 0.024 0.022 0.020 20 15 0.018 0.016 0.014 0.012 12 Cntrl y _ 0.02039 + 0.00266 x (? = 0.89) Cyanamide McPhersn etal. (1992). 13 14 15 16 17 Temperature frm budbreak t flwering ( C) lwest. The respnse at Kerikeri in 1997 varies substantially frm this pattern and we are unable t explain this. We culd find n published infrmatin n the effect f HC n the spread f budbreak apart frm a cmment that it prduced a mre cmpact budbreak perid (LinsleyNakes 1989). Time f flwering The midpint f flwering f untreated vines varied by nly 9 days during the fur seasns at three sites, and there was n bvius trend (Fig. 1). HC advanced flwering by 23 days at Kerikeri, the warmest site, but at Riwaka, the clest site, there was n advancement. In experiments described by Henzell et al. (1991), HC advanced flwering by 1 2 weeks at Te Puna in the Bay f Plenty. This is similar t the average 9day advancement we fund at Te Puke, which is near the site used by Henzell et al. (1991). There was a high crrelatin between the HCinduced advance in budbreak and the advance in flwering (r 2 = 0.92, Fig. 2). Hwever, the advance in flwering was just under half as much as the advance in budbreak. This is prbably the result f
282 New Zealand Jurnal f Crp and Hrticultural Science, 2001, Vl. 29 70 60 40 30 50 20 70 (A) Kerikeri (D) Kerikeri CD > Fig. 4 Amunt f budbreak (A, B, C) and flwering (D, E, F) n 'Hayward' kiwifruit (Actinidia delicisa) vines at Kerikeri, Te Puke, and Riwaka, New Zealand ver fur seasns (* indicates that vines treated with hydrgen cyanamide differ frm the cntrl vines P<0.05). CO 60 CD = 50 CD O.Q 40 O 30 13 20 O 70 ^ 60 (B) Te Puke (E) Te Puke 2 ^ D.Q E 3 50 40 30 20 (C) Riwaka Cntrl Cyanamtd (F) Riwaka 1996 1997 1998 1999 1996 1997 1998 1999 Year 1 cler temperatures being experienced between budbreak and flwering in vines that had their budbreak advanced by HC. Variatin in the rate f develpment frm budbreak t flwering (i.e., the reciprcal f the duratin between budbreak and flwering) is clsely related t the temperatures prevailing during that perid (r 2 = 0.89) with n cnsistent difference between the untreated and HCtreated vines (Fig. 3). The relatinship is similar t that fund by McPhersn et al. (1992) and Salinger et al. (1993) n untreated vines. Kerikeri data in 1998 were nt used in the regressin analysis because budbreak was unusually lw in bth the untreated vines (18%) and the treated vines (35%) fllwing winter temperatures that were dramatically warmer than usual (1.7 C warmer than the previus tw winters, Table 1). The amunt f flwering was als lw in bth treatments. Spread f flwering The applicatin f HC reduced the spread f flwering frm an average f 17 days in the untreated vines t 9 days in the treated vines (Table 2). Henzell et al. (1991) als fund that HC apprximately halved the spread f flwering. The rati fr the spread f flwering n the HCtreated vines t the untreated vines averaged ver the 4 years was 0.3 at Kerikeri, 0.7 at Te Puke, and 0.8 at Riwaka (Table 2). There was sme variatin in the rati frm year t year at each site. Amunt f budbreak The amunt f budbreak was highest n vines grwing at the clest site, Riwaka, and lwest at the warmest site, Kerikeri (Fig. 4). Budbreak increased with HC applicatin. This increase was greatest at the warmest site (46% average increase
McPhersn et al. Cyanamide effects n kiwifruit 283 Fig. 5 Respnse f: A, the amunt f budbreak; and B, the amunt f flwering t mean winter (MayJuly) temperatures at three sites ver 4 years. Anntatin is explained in Fig. 1. 1a.Q bud 'winter 2 )s a) num 60 50 40 c E 30 20 4 3 2 1 i i i i i i i "'.. 0 T6 R6^Ri ".. OT7 R7 ^*\. 8^.R8^^ Cntrl y=94.64.77x Cyanamide y= 86.73.21 x (f = 0.59) 1 ' 1 i R6 OR6 \. 0R9 R7 ^<:. ^O.. R8 O R8 0 i i 1 7 8 9 10 11 \. O K7 "' T7 0 T6 **J7'"". OTB'^6 7 "^^_ '" O K7 C[9 *.., 0 K9 # T7 Cntrl y =6.45 0.442 x (?* = 0.78) \ ^ Cyanamide y = 5.320.313 x (/ f 0 T9""" (^ = 0.84) 1 ' 1 1 OT9 > < 6 = 0.65) ^ * (A) 0K8 1 1 1 12 13 14 15 Mean winter temperature ( C) K8 (B). 0K8 K8 < at Kerikeri) but less at cler sites (Te Puke 25% and Riwaka 7%). Shuck & Petri (1995) fund in a warm area in suthern Brazil that HC increased the percentage budbreak frm 28 t 44% in 1 year, with n respnse the fllwing year. In Suth Africa, Allan et al. (1997) recrded an increase frm 23 t 46% budbreak. Richardsn et al. (1994) fund 3% HC applied at Kerikeri during the secnd week f August increased budbreak frm an average f 35% ver 3 years t 47%. This is a 36% increase ver the 3 years cmpared t the 46% ver the 4 years f the present experiment at the same site. Winter temperature had a majr impact n the amunt f natural budbreak (r 2 = 0.84, Fig. 5A) and n the budbreak f vines treated with HC. There was mre variability in the treated vines (r 2 = 0.59) perhaps resulting frm variatin in factrs such as drying time r applicatin technique which influence the efficacy f the HC spray (Henzell & Allisn 1993). Mean MayJuly (winter) temperatures were used as an index f winter chilling because Richardsn chill units and hurs belw 7 C are highly crrelated (r 2 = 0.98) with mean winter temperatures and cnfer n additinal advantage ver mean winter temperatures (W. P. Snelgar pers. cmm.). The respnse f budbreak t temperature n the treated vines was lwer than fr the untreated vines, cnsequently the difference between the
284 New Zealand Jurnal f Crp and Hrticultural Science, 2001, Vl. 29 natural budbreak and that f treated vines tended t increase with increasing temperature. Amunt f flwering The ttal number f flwers per winter bud n the untreated vines, increased frm an average f 0.9 at the Kerikeri, the warmest site, t 1.3 at Te Puke and 2.8 at Riwaka, the clest site (Fig. 4). In an earlier study at Kerikeri, Richardsn et al. (1995) fund a similar respnse t temperature frm seasn t seasn where the number f flwers were much higher in the year with the highest natural chilling. LinsleyNakes (1989) als fund that natural flwering was higher at the sites with higher winter chill units. The percentage f the flwers that were laterals r side flwers averaged 14% at Kerikeri, 13% at Te Puke, and 29% at Riwaka which is a pattern that wuld be expected with the mre prfuse flwering at the clest site. Other measurements in the Te Puke regin fund that the percentage lateral flwers averaged 18% ver an 8year perid (Henzell & Allisn 1993b). Applicatin f HC increased the ttal number f flwers that develped per winter bud at the tw warmest sites in all cases except 1997 at Kerikeri (Fig. 4). HC applicatin had n effect r reduced flwering at Riwaka. There was cnsiderable variatin frm year t year. The applicatin f HC slightly reduced this variatin (Fig. 4). Richardsn et al. (1994) als fund sme reductin in seasnal variability with HC applicatin, but large differences in flwer numbers were still evident and lateral flwers were nt cnsistently remved. HC reduced the percentage f lateral flwers frm 14 t 4% at Kerikeri, 13 t 7% at Te Puke, and 29 t 19% at Riwaka. Henzell & Brisce (1986), and Henzell & Allisn (1993b) fund that HC reduced lateral flwers n vines at Te Puke by a similar amunt t that recrded at Te Puke in the present experiment. Hwever they nte that cane diameter can affect the respnse f lateral flwers t HC applicatin. A significant reductin in the number f pr quality lateral flwers may be the nly benefit f applying HC t vines at cler sites like Riwaka. Much f the variatin in the ttal number f flwers per winter bud can be accunted fr by winter chilling. In the untreated vines, the number f flwers per winter bud decreased by 0.44 per 1 C increase in mean winter temperature (Fig. 5B). The number f flwers n the vines treated with HC als decreased with increasing temperature but the slpe was lwer than the untreated vines, as it was fr budbreak. Cnsequently, the respnse f flwer numbers t HC applicatin tended t increase with increasing temperatures. In a substantially warmer Suth African envirnment where kiwifruit flwer numbers are lw, LinsleyNakes (1989) fund that the respnse f flwering t HC was greatest at the clest sites. CONCLUSIONS Despite the imprtance f HC t the kiwifruit industry, there is nly limited published infrmatin t guide its use. Natural budbreak is later under warmer cnditins, but higher rates f develpment between budbreak and flwering result in the date f flwering varying little amng regins in New Zealand. When HC was applied t vines, budbreak ccurred 40 days later regardless f when natural budbreak wuld have ccurred. The advance in flwering that ccurred as a result f HC applicatin depended n the temperatures frm budbreak t flwering. Earlier budbreak and flwering will increase the risk f frst damage in sme areas. The perid ver which budbreak and flwering ccurred was cmpressed when HC was applied. This culd affect pllinatin if adverse weather ver the flwering perid reduced bee activity, r if the verlap with male vine flwering was substantially reduced. The applicatin f HC increased the amunt f budbreak and ttal flwer numbers at the warmest sites. This had a majr impact n fruit yields and the ecnmic viability f grwing kiwifruit at Kerikeri and Te Puke. HC als reduced the percentage f lateral flwer at all three sites and this may be sle benefit f applying HC at cl sites. High variability frm year t year is the result f winter chilling which accunted fr 84% f the variatin in the amunt f natural budbreak and 78% f the amunt f flwering. HC applicatin slightly reduces this variability but it certainly des nt "weatherprf the vines by negating any effect f winter temperatures. ACKNOWLEDGMENTS We thank the fllwing staff wh maintained vines and cllected data: Rbyn McQueen and Ted Dawsn, Kerikeri; Wendy Sctt, Philip Martin, and Janne Craig, Te Puke; Heather Adams, Jhn Campbell, Janne Stkes, and Greg Luptn, Riwaka. Thanks als t Helen Paul fr cllating and checking data. This wrk was funded by the New Zealand Fundatin fr Research, Science and Technlgy, Cntract N. CO6622.
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