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
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20418 |
| Date | 03 1900 |
| Creators | Brink, Johannes Cornelius (Jan-Cor) |
| Contributors | Fourie, Paul H., Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | x, 167 p. : ill. |
| Rights | Stellenbosch University |
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