Thesis (MSc)--Stellenbosch University, 2004. / Full text to be digitised and attached to bibliographic record. / ENGLISH ABSTRACT: The control of excessive vegetative growth is important in deciduous fruit orchards. Currently the plant growth regulator prohexadione-calcium (p-Ca) is used to control apple shoot growth in the Untited States of America and some European countries. The effect of P-Ca on the shoot and fruit growth of apples (Malus domestica B.), pears (Pyrus cummunis L.), plums (Prunus sa/icina L.) and nectarines (Prunus persica L.) was evaluated. Inhibition of shoot growth can effect fruit growth. Therefore I did a literature review on the fruit growth of pome- and stone fruit. Split pit, a physiological disorder associated with an increased fruit growth rate in stone fruit, was also investigated. During the course of the 2001 / 2002 season two trials were conducted in the Villiersdorp area of the Western Cape on 'Golden Delicious' and 'Granny Smith' apple trees. Single and multiple applications of P-Ca at different rates, with and without the surfactant Dash®, were applied. One of these trials was continued during the 2002 / 2003 season. In the 2001 / 2002 season, P-Ca reduced shoot growth in both trials on 'Golden Delicious'. The shoot growth of 'Granny Smith' was reduced in both trials where PCa was applied three or four times. There was an improvement in the fruit size of 'Golden Delicious' in both trials, but there was no improvement in the fruit size of 'Granny Smith'. In the 2002 / 2003 season, the single P-Ca application did not reduce shoot growth. Unfortunately 'Golden Delicious' was harvested before any data were obtained. Once again P-Ca had no effect on the fruit size of 'Granny Smith'. Dash® did not improve the effect ofP-Ca. In the 2002 / 2003 season we replicated one trial on five different pear cultivars in the Wolsely area of the Western Cape. Single and multiple applications of P-Ca at different rates were compared to a girdling treatment (2 weeks after full bloom). 'Early Bon Chretien', 'Rosemarie', 'Flamingo', 'Forelle' and 'Packham's Triumph' pear trees were used and Dash®was added to all 0f the treatments. P-Ca reduced shoot growth in all of the pear cultivars. Girdling reduced shoot growth only in 'Forelle'. P-Ca increased fruit set of 'Early Bon Chretien', 'Rosemarie' and 'Forelle', however, this was associated with a reduced fruit size of 'Early Bon Chretien' and 'Rosemarie'. Girdling did not increase fruit set, but increased fruit size of 'Flamingo' and 'Early Bon Chretien'. P-Ca reduced return bloom of 'Packham's Triumph' and 'Forelle', whereas girdling increased return bloom in all the cultivars except 'Packham's Triumph'. In the 2002 / 2003 season, trials were also conducted on 'Pioneer' and 'Songold' plums and 'May Glo' nectarine in the Wemmershoek and Stellenbosch area of the Western Cape. Single applications at different rates of P-Ca were applied. Dash® was added to all of the treatments. The higher rates of P-Ca reduced the shoot growth of 'Pioneer'. P-Ca only reduced shoot growth of 'Songold' initially and but did not reduce shoot growth of 'May Glo'. P-Ca had no influence on fruit size of 'Pioneer', 'Songold' or 'May Glo'. P-Ca did not aggravate the occurrence of split pit. In conclusion, P-Ca reduced shoot growth in apples and pears when applied at the appropriate rates. Although P-Ca reduced shoot growth of 'Pioneer' plum, more research needs to be done on stone fruit to optimise timing and rate of P-Ca applications. / AFRIKAANSE OPSOMMING: Die beheer van oormatige lootgroei is van kardinale belang in vrugtebome. Tans word die plantgroeireguleerder proheksadioon-kalsium (P-Ca) gebruik om die lootgroei van appels te beheer in die Verenigde State van Amerika en sekere lande in Europa. Die effek van P-Ca op lootgroei en vruggrootte is in proewe op appels (Malus domestica B.), pere (Pyrus cummunis L.), pruime (Prunus salicina L.) en nekatriens (Prunus persica L.) geëvalueer. Aangesien lootgroei inhibisie moontlik vruggroei kan vesnel, is 'n literatuurstudie oor die vruggroei van kern-en steenvrugte gedoen. Die ontwikkelling van gesplete pit by steenvrugte ('n fisiologiese defek geassosieer met versnelde vruggroei) is ook ondersoek. Gedurende die 2001 / 2002 seisoen is P-Ca in twee afsonderlike proewe in die Villiersdorp area van die Wes Kaap geëvalueer. Enkel en veelvuldige toedienings van verskeie konsentrasies P-Ca, met en sonder die benatter Dash", is op 'Golden Delicious' en 'Granny Smith' bome toegedien. Een proef is herhaal gedurende die 2002 / 2003 seisoen. In die 2001 /2002 seisoen het die P-Ca behandelings in beide proewe die lootgroei van 'Golden Delicious' verminder. Die lootgroei van 'Granny Smith' is in beide proewe verminder waar P-Ca 3 of 4 keer toegedien is. Die vruggrootte van 'Golden Delicious', maar nie 'Granny Smith' nie, is in beide proewe deur die P-Ca verbeter. In die 2002 / 2003 seisoen kon die enkeltoedienings van P-Ca nie die lootgroei verminder van 'Golden Delicious' of 'Granny Smith' nie. 'Golden Delicious' is geoes voor enige inligting oor die vruggrootte ingesamel kon word. Weereens het PCa geen invloed op die vruggrootte van 'Granny Smith' gehad nie. Dash® het nie die effek van P-Ca verbeter nie.In die 2002 / 2003 seisoen is proewe met P-Ca gedoen op 5 verskillende peer kultivars in die Wolsely area van die Wes Kaap. P-Ca is teen verskillende konsentrasies, met enkel en veelvuldige bespuitings toegedien en vergelyk met 'n ringelerings behandeling (2 weke na volblom). 'Early Bon Chretien', 'Rosemarie', 'Flamingo', 'Forelle' en 'Packham's Triumph' bome is gebruik en die benatter Dash® is by al die behandelings gevoeg P-Ca toedienings het lootgroei verminder in 'Early Bon Chretien', 'Rosemarie', 'Flamingo', 'Forelle' en 'Packham's Triumph'. Ringelering kon slegs die lootgroei van 'Forelle' verminder. P-Ca het die vrugset van 'Early Bon Chretien', 'Rosemarie'en 'Forelle' verhoog. Die toename in vrugset het gelei tot 'n afname in die vruggrootte van 'Early Bon Chretien' en 'Rosemarie'. Ringelering het die vruggrootte van 'Flamingo' en 'Early Bon Chretien' verbeter. P-Ca het 'n afname in die hoeveelheid reproduktiewe knoppe in die volgende seisoen, van 'Packham's Triumph' en 'Forelle' veroorsaak. Ringelering het 'n toename in die hoeveelheid vegetatiewe knoppe in die volgende seisoen gehad vir al die kultivars, behalwe 'Packham's Triumph'. Geduerende dieselfde seisoen is daar ook proewe gedoen op 'Pioneer' en 'Songold' pruime en 'May Glo' nektarienbome in onderskeidelik die Wemmershoek en Stellenbosch areas van die Wes Kaap. Bome is met enkel toedienings van verskillende konsentrasies P-Ca behandel en die benatter Dash® is by al die behandelings bygevoeg. Die hoër dosisse P-Ca het die lootgroei van 'Pioneer' verminder. P-Ca kon slegs die aanvanklike lootgroei op 'Songold' verminder en kon nie lootgroei van 'May Glo' beperk nie. P-Ca het geen invloed op die vruggrootte van 'Pioneer', 'Songold' of 'May Glo' gehad nie. P-Ca het nie die voorkoms van gesplete-pit vererger nie. Om saam te vat kan gesê word dat P-Ca lootgroei op appels en pere goed beperk teen die regte konsentrasies. Alhoewel P-Ca lootgroei suksesvol beheer het op 'Pioneer', moet daar meer werk gedoen word op steenvrugte.