Effect of kaolin applications on pome fruit

Le Grange, Monique (2001-04)

Thesis (MScAgric)--Stellenbosch University, 2001.

Thesis

ENGLISH ABSTRACT: Sunburn is a major problem in the apple industry worldwide. A kaolin product, M-97- 009 (100% kaolin), originally developed for insect control, was evaluated for its efficacy in controlling sunburn on pome fruit. Trials were conducted over two seasons in two different areas of the Western Cape, South Africa. During the first season, 'Royal Gala', 'Fuji' and 'Granny Smith' apples were evaluated in the Koue Bokkeveld. The kaolin was mixed with water and applied to the trees by means of a hand-gun regularly throughout the season. In addition to the effect on sunburn, effects on yield, colour development, snout beetle damage and other defects were determined. Sunburn was reduced on all the cultivars tested, although not significantly on 'Granny Smith'. Inconsistent effects on yield parameters were observed. The applications significantly reduced red colour on 'Fuji', but this problem was rectified by an improved application technique the following season. During the second season, additional apple cultivars and 'Rosemarie' pears were included in the trials. The apple trials were conducted in the Elgin area, and the 'Rosemarie' trial in the Koue Bokkeveld. Surround™ (95% kaolin) was applied to the trees by means of a commercial "blower". The effects on sunburn, yield, colour development and fruit maturity were determined. In contrast to the previous season, sunburn was not reduced on any of the cultivars examined. Yield parameters were not affected except in the case of 'Royal Gala' where the number of fruit was increased, and 'Cripps' Pink' where the number of fruit was reduced. Fruit colour was not affected in the apple cultivars, but chroma of 'Rosemarie' pears was reduced, indicating a less intense colour. The kaolin applications had a variable effect on fruit maturity. The effect of the foliar applications on photosynthetic photon flux density (PPFD), photosynthetic rate, stomatal conductance and transpiration rate was determined. In addition to these spot measurements, photosynthetic light response curves were determined. Measurements were taken on both the inner and outer canopies The applications significantly reduced photosynthetic rates in the inner canopy and reduced the apparent quantum efficiency of leaves on the outer canopy. No significant effect on PPFD was found. It appears that the white coating reflects light and allows less light to penetrate the leaf, thus reducing photosynthesis. Surround™ treatments could not counteract the damaging effects of the high temperatures experienced in the Western Cape during this season and was not effective as a control measure for sunburn. This does not appear to be a commercially viable solution for the sunburn problem and it would be worthwhile to investigate the use of alternative options, such as evaporative cooling.

AFRIKAANSE OPSOMMING: Sonbrand is een van die grootste probleme wat wêreldwyd in die appelbedryf ondervind word. 'n Nuwe produk, M-97-009 (100% kaolien), is oorspronklik ontwikkel vir insekbeheer in geïntegreerde plaagbeheer, maar daar is beweer dat dit moontlik sonbrand op kemvrugte kan verminder. Proewe is oor twee seisoene uitgevoer in die Koue Bokkeveld en ook in die Grabouw-omgewing in die Wes-Kaap. Tydens die eerste seisoen is die effek van M-97-009 op 'Royal Gala', 'Fuji' en 'Granny Smith' appels beoordeel. Die kaolien is met water gemeng en deur die loop van die seisoen met 'n handspuit op die bome gespuit. Die effek van die produk op sonbrand, oesgrootte, vruggrootte, kleurontwikkeling, kalanderskade en ander defekte is bepaal. Sonbrand is op alle kultivars verminder, alhoewel nie betekenisvolop 'Granny Smith' nie. Die effek van kaolien op oesparameters was rue konsekwent nie. kleurontwikkeling op 'Fuji' benadeel, heel moontlik Die toedienings het as gevolg van die toedieningstegniek. Met verbeterde toedieningsmetodes die volgende seisoen, is kleurontwikkeling van 'Fuji' nie benadeel nie. Tydens die tweede seisoen is die effek van kaolien op nog appelkultivars en 'Rosemarie' pere ge-evalueer. Die appelproewe is in Elgin uitgevoer, terwyl die 'Rosemarie'-proefin die Koue Bokkeveld uitgelê is. Surround™ (95% kaolien) is met kommersiële spuitpompe toegedien. Weereens is die effek van die produk op sonbrand, oesgrootte, vruggrootte, kleurontwikkeling en vrugrypheid bepaal. Sonbrand is nie verminder nie. Vruglading tydens oes is nie betekenisvol beïnvloed nie, behalwe in die geval van 'Royal Gala' waar die vruglading verhoog is, en 'Cripps' Pink' waar daar minder vrugte op die gespuite bome was. Die Surround™ toedienings het geen uitwerking op kleur van appels gehad nie, maar het die chromawaarde van 'Rosemarie' pere verlaag, d.w.s die vrugkleur was minder intens. Die kaolienspuite het 'n uiteenlopende effek op vrugrypheid gehad. Fotosintetiese foton vloeddigtheid (FFV), fotosintesetempo, huidmondjieweerstand en transpirasietempo is gemeet en ligreponskurwes van beide die buitenste en binneste blaardak is bepaal. Die Surround™ toedienings het fotosintese van blare ill die binneste gedeelte van die blaardak verminder en die kwantumdoeltreffendheid van blare op die buitenste deel van die blaardak verminder. Geen betekenisvolle effek is op FFV gekry nie. Dit wil voorkom asof die wit laag kaolien op die bome lig weerkaats en veroorsaak dat minder lig na die blaar deurdring. Dit verminder dan die fotsintesetempo. Met die baie warm weer wat in die Wes-Kaap gedurende die tweede seisoen ervaar is, kon die SUITound™behandelings nie sonbrand verhoed nie. Dit wil voorkom asof Surround™ nie 'n baie doeltreffende oplossing in kommersiële boorde sal wees nie. Alternatiewe oplossings, soos byvoorbeeld evaporatiewe verkoeling, saloorweeg moet word.

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