Investigating the vegetative development and yield of pecan

Dedekind, Ruben Egmund (2020-03)

Thesis (MScAgric)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: Like other deciduous trees grown in regions that experience warm winters and low winter chilling, pecans suffer from low and sporadic bud break. This often has negative implications for vegetative growth and development of the trees, especially in younger orchards that are still filling space. Furthermore, the yield will often be reduced as a result of reduced vegetative development as well as a lack of synchronisation in the flower development. Application of hydrogen cyanamide (HC) formulated as Dormex® was evaluated on two pecan cultivars, ‘Wichita’ and ‘Navaho’, grown in the Prieska region, Northern Cape, South Africa. Three different concentrations were evaluated on two application dates. Trees were assessed for time of bud break, final percentage of total bud break, shoot growth and yield. Additionally, the effect of HC on the synchronisation of the flowering periods of ‘Wichita’ as the main cultivar and ‘Navaho’ as the cross pollinator, was assessed. During 2018, after a relatively cold winter, Dormex® had a relatively small effect on the bud break parameters of ‘Wichita’ trees. On ‘Navaho’ trees, all treatments were effective at increasing the percentage bud break. During 2019, a warmer winter was experienced. On ‘Wichita’, an early application four weeks before expected bud break (4WBBB) was more effective at advancing bud break than a later treatment, two weeks before expected bud break (2WBBB). Dormex® at 4% resulted in a significantly higher initial bud break percentage than the control on both cultivars and Dormex® at 4% and 2%, resulted in a significant increase in the final percentage bud break during the warmer year. These results indicate the total bud break (vegetative and reproductive buds) and do not indicate improved vegetative development or improved flowering per se. No increase was seen in vegetative bud break during the 2019 season on either cultivar and this should be evaluated further. Dormex® at 4% 4WBBB resulted in a significantly higher yield on ‘Wichita’ compared to the control during the first season and this needs to be followed up during 2020. No increase in yield was seen on ‘Navaho’. The best result for improving the synchronisation of the flowering periods was achieved by treating ‘Wichita’ with 4% Dormex® 4WBBB to significantly advance bud break, while leaving ‘Navaho’ trees untreated. No signs of phytotoxicity on leaves or shoots were observed for any of the treatments. In conclusion, the effect of HC on improving the vegetative development of these cultivars could not be established, as no distinction was made between vegetative and reproductive buds during bud break and more research is required. HC applications did however influenced time and percentage bud break. It is possible that the effect could be extended towards yield through better synchronisation of the flowering periods, but this effect can only be quantified during 2020 and thus could not be included in this thesis. The effect of notching shortly before bud break was investigated on young, nonbearing ‘Wichita’ pecans grown in the Villiersdorp region, Western Cape, South Africa. The effect on bud break, shoot number, shoot length and branch angle was evaluated. On two-year-old wood, notching was unable to increase bud break or shoot number and was influenced to a certain extent by the size of the bud. No increases were seen in shoot length on two-year-old wood. On one-year-old wood, notching significantly increased the number of. In conclusion, notching can increase lateral vegetative development of young trees if carried out on younger wood and could be used as a valuable tool for improving vegetative development and ensuring more successful orchard establishment.

AFRIKAANSE OPSOMMING: Pekanneutbome wat gevestig word in areas met gematigde winters is geneig om lae en wisselvallige knopbreek te toon, soortgelyk aan ander bladwisselende gewasse wat onder soortgelyke toestande ontwikkel. Hierdie onvoorspelbare knopbreek het tot gevolg dat die ontwikkeling van jong bome benadeel word wat dus die vestigingsperiode van boorde onnodig verleng. Die verminderde vegetatiewe ontwikkeling beperk neutopbrengs deurdat drahout beperk word en verder beïnvloed die wisselvallige knopbreek blomontwikkeling, wat opbrengste direk beperk. Toediening van waterstofsianamied (geformuleer as Dormex®) is op twee pekanneutkultivars, ‘Wichita’ en ‘Navaho’, geëvalueer in Prieska in die Noord-Kaap provinsie van Suid-Afrika. Drie verskillende konsentrasies is op twee toedieningstadiums geëvalueer. Die datum van knopbreek, finale persentasie knoppe wat gebreek het, totale lootgroei en die opbrengs per boom is bepaal. Die effek van waterstofsianamied op die sinchronisasie van die blomtye van 'Wichita' (die hoofkultivar) en 'Navaho' (die kruisbestuiwer) is ook bepaal. Gedurende 2018, na 'n koue winter, het waterstofsianamied 'n relatiewe klein effek op die knopbreek parameters van 'Wichita' gehad. Op 'Navaho' bome het al die behandelings finale knopbreek verhoog. Gedurende 2019 is minder koue-eenhede geakkumuleer en in 'Wichita' was 'n vroeë toediening vier weke voor verwagte knopbreek (4WBBB) meer effektief om knopbreek te bevorder as 'n later behandeling, twee weke voor verwagte knopbreek (2WBBB). Dormex® teen 4% het aanvanklik ʼn hoër persentasie knopbreek getoon teenoor die kontrole vir beide kultivars, en 4% en 2% Dormex® het 'n betekenisvolle toename getoon in die finale hoeveelheid knopbreek in die warmer jaar. Hierdie resultate wys net die totale knopbreek en dus is die verhoogte knopbreek nie ‘n aanduiding van ‘n verhoogde vegetatiewe groei of ‘n verhoogte aantal blomme per se nie. In die 2019 seisoen, is geen toename in vegetatiewe knopbreek waargeneem nie op beide kultivars nie en die resultaat moet verder evalueer word. Op ‘Wichita’ het die toediening van 4% Dormex® 4WBBB gelei tot 'n betekenisvolle hoër opbrengs in vergelyking met die kontrole gedurende die eerste seisoen en die effek moet opgevolg word gedurende 2020. Op 'Navaho' was daar egter geen toename in opbrengs nie. Die beste resultaat in verbetering van die blomtyd sinchronisasie is bereik met ʼn toediening van 4% Dormex® 4WBBB op 'Wichita', terwyl 'Navaho' bome onbehandeld gelaat word. Geen tekens van fitotoksisiteit is waargeneem in enige behandeling nie. Ten slotte kon die effek van waterstofsianamied op die verbetering van die vegetatiewe ontwikkeling op die kultivars nie bepaal word nie, aangesien daar nie onderskeid gemaak is tussen vegetatiewe en reproduktiewe knoppe gedurende knopbreek nie en meer navorsing word benodig. Waterstofsianamied het wel die tyd en persentasie knopbreek beïnvloed. Dit is moontlik dat die effek uitgebrei kan word na opbrengs deur beter sinchronisasie van die blomperiodes, maar die effek kan eers gedurende 2020 gekwantifiseer word en kon dus nie ingesluit word in die tesis nie. Die effek van kerfies kort voor knopbreek is op jong, nie-draende 'Wichita' pekanneut bome ondersoek in die Villiersdorp area, Wes-Kaap, Suid-Afrika . Die effek op die knopbreek, aantal lote, loot lengte en takhoeke is geëvalueer. Op twee-jaaroue hout kon die kerfies nie knopbreek of die aantal lote verhoog nie en dit is moontlik dat knopbreek tot 'n mate beïnvloed is deur die grootte van die knop. Geen verhogings is gesien in lootlengte op twee-jaar-oue hout nie. Op een-jaar-oue hout kon kerfies egter die aantal lote betekenisvol verhoog. Ter afsluiting, kerfies op jong bome kon laterale vegetatiewe ontwikkeling verhoog. Dit kan gebruik word as 'n waardevolle hulpmiddel om vegetatiewe ontwikkeling te verbeter en om 'n meer suksesvolle boordontwikkeling te verseker.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107830
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