Thesis (PhD(Agric))--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Despite adherence to fungicide spray schedules and label recommendations, table and wine grape producers invariably suffer crop losses when environmental conditions are conducive to fruit and foliar pathogens. Registered fungicides are effective and poor control is often attributed to: 1) improper spray timing, 2) reduced sensitivity to fungicides in the pathogen populations, and 3) poor spray deposition. Spray timing, management of fungicide resistance and the epidemiology of Botrytis cinerea have been thoroughly researched under South African conditions on grape crops. However, limited research regarding spray deposition exists in South Africa, probably due to a lack of proper spray deposition assessment protocols. To determine minimum spray deposition quantity and quality levels needed for effective B. cinerea control, bunches and leaves of table (Waltham Cross) and wine grapes (Chenin blanc) were sprayed at various stages using different volumes with a precision spray gun. A deposition assessment protocol using fluorometry, photomicrography and digital image analyses was improved. Deposition values correlated favourably with Botrytis infection. Increasing spray volume increased spray deposition; however, at a certain point, deposition quality remained constant and B. cinerea infections did not decrease significantly with increasing spray volume, indicating the importance of both spray deposition quantity and quality. Fluorescent pigment area that effected 75% control of B. cinerea infection (FPC75 values) was calculated for leaves, pedicels and receptacles at different growth stages. The FPC75 values obtained in this study can be used as benchmarks to evaluate future spray application. In order to study the optimisation of spray deposition with existing application technology (air blast and air shear sprayers) in commercial vineyards, spray deposition quantity and quality values were assessed from leaves and structural bunch parts of wine (Chenin blanc) and table grapes (Waltham Cross) and compared with FPC75 values. Spray trials were conducted at different growth stages at current best-practice recommendations, and with a range of spray volumes but with spray mixture concentration amended accordingly (i.e. fixed dosage per hectare). Spray trails indicated that deposition levels following current best-practice spray application were sub-optimal to control B. cinerea infections on bunches and leaves. Deposition values between air blast and air shear sprayers were generally similar. The air blast sprayer resulted in higher deposition levels with diluted spraying and increased spray volume; however, when dosage per hectare was kept constant, no significant differences were calculated between spray volumes (250-1000 L/ha), indicating that this sprayer can as effectively but more efficiently be used at lower spray volume. The air shear were not as efficient at higher spray volumes (>500 L/ha), but was superior at low volume concentrate application (≈250 L/ha at 4× concentration). This study clearly demonstrated the efficacy and cost-saving potential in optimising spray application with respect to application technology. / AFRIKAANSE OPSOMMING: Wingerdprodusente kan oesverliese ondervind indien omgewingstoestande bevorderlik is vir swampatogene. Siektes word onvoldoende beheer ten spyte van die nakoming van korrekte swamdoder aanbevelings. Geregistreerde swamdoders is effektief, mits die vatbare plantdele voldoende spuitbedekking ontvang. Onvoldoende siekte beheer kan gewoonlik toegeskryf word aan: 1) verkeerde spuit tydsberekening, 2) vermindere sensitiwiteit in patogeen-populasies teen swamdoders, en 3) swak spuitbedekking. Spuit tydsberekening, die bestuur van weerstand teen swamdoders en die epidemiologie van Botrytis cinerea is deeglik onder Suid-Afrikaanse toestande nagevors. Nietemin is daar beperkte navorsing oor spuitbedekking, waarskynlik weens 'n gebrek aan behoorlike spuitbedekking assesseringsprotokol. Om te bepaal hoeveel spuitbedekking (% area bedek deur fluoresserende pigment) nodig is om 75% van B. cinerea infeksies (FPC75 waardes) op vatbare wingerddele te beheer, is druiwetrosse en blare van tafel- en wyndruiwe (Waltham Cross en Chenin blanc, onderskeidelik) op verskillende groei stadiums en spuitvolumes in die laboratorium gespuit. ‘n Assesseringsprotokol van spuitbedekking op vatbare druifdele en blare is ontwikkel deur gebruik te maak van fluorometrie, fotomikrografie en digitale beeldanalise. Spuitbedekking het goed met Botrytis infeksies gekorreleer. Toenemende spuitvolume het bedekking laat toeneem, maar egter net tot 'n sekere punt, waar die kwantiteit van die bedekking nog toegeneem het, maar die kwaliteit van bedekking en B. cinerea infeksies nie beduidend toegeneem het nie. Dit is ‘n aanduiding van die belangrikheid van beide die kwantiteit en kwaliteit van spuitbedekking. Die FPC75 waardes wat in hierdie studie verkry is, kan as drempelwaardes om toekomstige spuittoediening te evalueer, gebruik word. Ten einde spuitbedekking met bestaande tegnologie (druk en waaierpomp spuitmasjiene) te optimiseer, is kommersiële wyn- en tafeldruiwe (Chenin blanc en Waltham Cross, onderskeidelik), volgens huidige spuit aanbevelings vir wingerde tydens verskillende groeistadiums en met ‘n reeks van verskillende spuitvolumes gespuit. Die konsentrasie van die spuitmengsel is dienooreenkomstig gewysig, i.t.v. ‘n vaste dosis per hektaar ongeag die spuitvolume. Bedekkingswaardes is met FPC75 waardes vergelyk en het aangedui dat kommersiële spuit aanbevelings aan produsente sal lei tot sub-optimale beheer van B. cinerea op beide blare en druiwetrosse. In die algemeen was bedekkingswaardes vir beide druk- en waaierpomp spuitmasjiene soortgelyk. Vir die waaierpomp teen verskillende spuitvolumes en aanbevole konsentrasie het ‘n toename in spuitvolumes tot hoër beddekingswaardes gelei, maar indien die dosis per hektaar van die spuitmengsel konstant behou is, is geen betekenisvolle verskille tussen spuitvolumes (250-1000 L/ha) voorspel nie. Hierdie dui aan dat die waaierpomp net so doeltreffend, maar meer effektief teen laer spuitvolumes gebruik kan word. Die drukpomp was nie so doeltreffend teen hoër spuitvolumes (> 500 L/ha) nie, maar was aansienlik beter by lae volume konsentraat toediening (≈ 250 L/ha op 4 × konsentrasie). Die studie toon duidelik die doeltreffendheid en moontlike kostebesparing moontlikhede deur bespuiting relatief tot bespuitingstegnologie te optimiseer. / Department of Plant Pathology, National Research Foundation, THRIP, Deciduous Fruit Producers’ Trust, Winetech, Bayer, BASF, Dow Agrosciences, DuPont, Syngenta, Nexus, Terason, UAP and Wenkem for financial assistance