Source and identity of insect contaminants in export consignments of table grapes
Date
2005-03
Authors
Journal Title
Journal ISSN
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Publisher
Stellenbosch : University of Stellenbosch
Abstract
The South African table grape industry exports approximately 60% of the table
grapes produced. A major threat to the export of these grapes is the phytosanitary risk
that insect pests pose. This study was conducted in the Hex River Valley, South
Africa’s main table grape producing area. The aim of this study was to reduce the
number of phytosanitary rejections from insects on table grapes from the Hex River
Valley. Thus the main objectives of the study were to identify the most important
phytosanitary pests in the Hex River Valley; the determination of their presence in the
vineyards with possible means to control them; and to assess the possibility of using
postharvest quarantine treatments in the Western Cape. Further aims were to
determine the effect of different colour harvesting crates on the phytosanitary pests and
whether the phytosanitary pests infested the grapes via packhouses.
The most important phytosanitary pests of table grapes of the Hex River Valley
are in order of importance: Phlyctinus callosus (Schonherr) (Coleoptera: Curculionidae),
Epichoristodes acerbella Walker (Lepidoptera: Tortricidae), Planococcus ficus
(Signoret) (Hemiptera: Pseudococcidae), Ceratitis capitata (Wiedemann) (Diptera:
Tephritidae), Gonocephalum simplex Fabricius (Coleoptera: Tenebrionidae) and
Dysdercus fasciatus Signoret (Hemiptera: Pyrrhocoridae). 12.71% of rejections were
from species that were not identified, while a further 33% of the rejections were possibly
identified incorrectly.
Phytosanitary control of P. callosus appeared to be far more effective using
Plantex® than pesticides. Weather conditions appeared to affect the abundance of P.
callosus, especially warm weather, while bunches harboured less P. callosus later in
the day. Control of E. acerbella with DiPel® (Bacillus thuringiensis var. kurstaki)
appeared to at least reduce the population within the vineyards, and so its use is
recommended. P. ficus is a non-actionable species for the USA market and is not
listed as a phytosanitary pest for the Israeli market and so should not be causing any
phytosanitary rejections. C. capitata appeared to be successfully controlled by the fruit
fly sterile release program and the cold sterilisation it currently undergoes. G. simplex
caused few rejections. It is still unclear where this pest infests the grapes, as it was found in both the field and in the packhouses. D. fasciatus occurrence on grapes was
probably accidental. It was shown that picking during the early and late parts of the
day, when this species was less active, reduced its occurrence in bunches. Gryllus
bimaculatus (De Geer) (Orthoptera: Gryllidae), although not reported as a reason for
rejections in table grapes for the past two years, was an actionable species that was
present in large numbers in the Hex River Valley. There was a strong correlation
between increasing quantities of pesticides and higher abundances of G. bimaculatus.
It appeared to be an indicator of the overuse of pesticides. Results of this study
showed that infestation by the phytosanitary pests came from neighbouring vineyards.
The creation of barriers to prevent the movement of these pests between vineyards is
suggested.
Methyl bromide is the most commonly used postharvest quarantine treatment.
Owing to the ozone-depleting properties of methyl bromide, it is scheduled to be
outlawed in many countries from 2005. Alternative postharvest treatments are
irradiation, extreme temperatures, forced air, vapour-heat treatments and the use of
controlled atmospheres. Irradiation treatments appeared to control the pests at doses
that do not damage the grapes. Controlled atmosphere treatments also have a high
probability of success, although more research is required on this treatment. Low
temperature treatments are relatively cheap as most exported fruit already undergoes
cold storage, and appears to control species in the families Pseudococcidae and
Tephritidae, although further research is required for the other pest.
Colour or location of the harvesting crates in the vineyards appeared not to
influence the number of phytosanitary pests collected, as they were not attracted to
these crates.
Description
Thesis (MScAgric (Conservation Ecology and Entomology)--University of Stellenbosch, 2005.
Keywords
Dissertations -- Conservation ecology and entomology, Theses -- Conservation ecology and entomology, Table grapes -- Diseases and pests -- Control, Table grapes -- South Africa -- Hex River Valley, Table grapes -- Postharvest diseases and injuries, Insect pests -- Control -- South Africa -- Hex River Valley