Spelling suggestions: "subject:"table grapes -- diseases anda tests"" "subject:"table grapes -- diseases anda pesar""
1 |
Development of a pest management system for table grapes in the Hex River ValleyDe Villiers, Marelize 03 1900 (has links)
Thesis (PhD (Agric) (Conservation Ecology and Entomology))--University of Stellenbosch, 2006. / A study was performed to develop a generic pest monitoring system for sampling the
main table grape pests in vineyards in the Hex River Valley, Western Cape Province
of South Africa. The presence of phytophagous and predatory mites on cover crop
plants was also investigated as this may contribute to biological control of the
phytophagous mites in vines. Life table studies for Epichoristodes acerbella
(Walker), an important phytosanitary pest, were conducted to determine whether or
not this pest was sensitive to high temperatures. Information gained from the latter
can also be used for breeding purposes in the possible future development of a sterile
insect technique (SIT) programme to control this pest.
The sampling system consisted of inspecting 20 plots of five vines per plot per one to
two hectares. The top fork of each of the five vines per plot was examined for
Planococcus ficus (Signoret) to a distance of within 30 cm of the stem, as well as the
distal 15 cm of one cane per vine for the presence of P. ficus and damage caused by
Phlyctinus callosus Boh. One bunch per vine was examined for insect damage or
presence, and one leaf per vine for the presence of leaf infesting arthropods, such as
Tetranychus urticae Koch, P. ficus and Frankliniella occidentalis (Pergande).
Corrugated cardboard bands, tied around the stem of one vine per plot, were used to
monitor activity of P. callosus. Blue sticky traps, at a density of four to five traps per
one to two hectares, were used to monitor activity of F. occidentalis. Pheromone
traps, at a density of one trap per one to two hectares, were used to monitor activity of
P. ficus, E. acerbella and Helicoverpa armigera (Hübner). All the above-mentioned
inspections were done at two-weekly intervals, except traps for E. acerbella and H.
armigera, which were inspected weekly. In each of the rows in which the sample
plots were situated, one leaf of each of the cover crop plant species was examined for
the presence of phytophagous mites and their predators. The abundance and
distribution of cover crop plants were determined using a co-ordinate sampling
system. Cover crop sampling was done at monthly intervals.
The current threshold for P. ficus is 2% stem infestation, which is reached when more
than 65 males per pheromone trap are recorded. Counting mealybugs on the sticky
pads in the pheromone traps is time consuming. However, the number of grid blocks
on the sticky pad with males present can be counted. When P. ficus males are found in 27 blocks on the sticky pad, stem inspections should commence. Due to the spatial
association between P. ficus bunch and stem infestation, stem infestation could give
an indication of where bunch infestation could be expected.
The use of blue sticky traps for predicting halo spot damage, caused by F.
occidentalis, is not recommended. The presence of thrips on the vine leaves could not
give an indication of where to expect bunch damage, since thrips on the leaves and
halo spot damage were not spatially associated. A suitable sampling method for F.
occidentalis still needs to be developed. The monitoring system described here can
only provide information on the infestation status of the vineyard.
For E. acerbella, H. armigera and P. callosus, the traps and cardboard bands could be
used to identify vineyards where these pests are present and therefore, where
phytosanitary problems may arise. The presence of P. callosus under the bands was
spatially associated with P. callosus damage and could be used as an indicator of the
latter. The presence of drosophilid flies in the bunches could not be used as an
indicator of the presence of E. acerbella in the bunches. If 5% bunch damage is used
as an economic threshold for E. acerbella and P. callosus, there will be a good chance
of not under spraying if control measures are applied at 1% bunch damage.
Epichoristodes acerbella favoured more moderate constant temperatures, with
constant temperatures of 28°C and above being unfavourable for development.
The economic threshold for Tetranychus urticae Koch is six mites per leaf, or if
presence-absence sampling is used, 11 to 29% leaf infestation. Three important
predatory mites, that kept T. urticae under control, were found in the Hex River
Valley, namely Euseius addoensis (Van der Merwe & Ryke), Neoseiulus californicus
(McGregor) and an undescribed phytoseiid in the genus Typhlodromus. Various
cover crop plants served as hosts for T. urticae and predatory mites. The presence of
these plants created suitable conditions for the survival of these mites and may have
influenced their presence on the vine leaves.
In the case of phytosanitary pests, both field and pack shed inspections can be used to
conclude with a 99% degree of certainty that infestation levels in the pack shed will
be 10% or less, since similar results for both methods were obtained. However, more
than 20 plots will have to be inspected.
|
2 |
Characterisation and management of trunk disease-causing pathogens on table grapevinesBester, Wilma 04 1900 (has links)
Thesis (MScAgric)--University of Stellenbosch, 2006. / ENGLISH ABSTRACT: Phaeomoniella chlamydospora, Eutypa lata, Phomopsis, Phaeoacremonium, and
Botryosphaeria spp. are important trunk disease pathogens that cause premature decline and
dieback of grapevine. Previous research has focused primarily on wine grapes and the incidence
and symptomatology of these pathogens on table grapes were largely unknown. A survey was
therefore conducted to determine the status and distribution of these pathogens and associated
symptoms in climatically diverse table grape growing regions. Fifteen farms were identified in
the winter rainfall (De Doorns, Paarl and Trawal) and summer rainfall (Upington and
Groblersdal) areas. Samples were taken in July and August 2004 from Dan-ben-Hannah
vineyards that were 8 years and older. Distal ends of arms were removed from 20 randomly
selected plants in each vineyard. These sections were dissected and isolations were made from
each of the various symptom types observed: brown or black vascular streaking, brown internal
necrosis, wedge-shaped necrosis, watery necrosis, esca-like brown and yellow soft wood rot, as
well as asymptomatic wood. Fungal isolates were identified using molecular and morphological
techniques. Pa. chlamydospora was most frequently isolated (46.0%), followed by
Phaeoacremonium aleophilum (10.0%), Phomopsis viticola (3.0%), Botryosphaeria obtusa
(3.0%), B. rhodina (2.2%), B. parva (2.0%), Fusicoccum vitifusiforme (0.6%), B. australis, B.
dothidea and an undescribed Diplodia sp. (0.2% each), while E. lata was not found. Most of
these pathogens were isolated from a variety of symptom types, indicating that disease diagnosis
can not be based on symptomatology alone. Pa. chlamydospora was isolated from all areas
sampled, although most frequently from the winter rainfall region. Pm. aleophilum was found
predominantly in Paarl, while P. viticola only occurred in this area. Although B. obtusa was not
isolated from samples taken in De Doorns and Groblersdal, it was the most commonly isolated
Botryosphaeria sp., being isolated from Upington, Paarl and Trawal. B. rhodina occurred only
in Groblersdal and B. parva in Paarl, Trawal and Groblersdal, while B. australis was isolated
from Paarl only. The rest of the isolates (33%) consisted of sterile cultures, Exochalara,
Cephalosporium, Wangiella, Scytalidium, Penicillium spp. and two unidentified basidiomycetes,
which were isolated from five samples with yellow esca-like symptoms from the Paarl area. These findings clearly illustrate that grapevine trunk diseases are caused by a complex of fungal
pathogens, which has serious implications for disease diagnosis and management.
Protection of wounds against infection by any of these trunk disease pathogens is the
most efficient and cost-effective means to prevent grapevine trunk diseases. However, previous
research on the effectiveness of chemical pruning wound protectants has mostly focused on the
control of Eutypa dieback only. Fungicide sensitivity studies have been conducted for Pa.
chlamydospora, P. viticola and Eutypa lata, but no such studies have been conducted for the
pathogenic Botryosphaeria species from grapevine in South Africa. Ten fungicides were
therefore tested in vitro for their efficacy on mycelial inhibition of the four most common and/or
pathogenic Botryosphaeria species in South Africa, B. australis, B. obtusa, B. parva and B.
rhodina. Iprodione, pyrimethanil, copper ammonium acetate, kresoxim-methyl and boscalid
were ineffective in inhibiting the mycelial growth at the highest concentration tested (5 μg/ml;
20 μg/ml for copper ammonium acetate). Benomyl, tebuconazole, prochloraz manganese
chloride and flusilazole were the most effective fungicides with EC50 values for the different
species ranging from 0.36-0.55, 0.07-0.17, 0.07-1.15 and 0.04-0.36 μg/ml, respectively. These
fungicides, except prochloraz manganese chloride, are registered on grapes in South Africa and
were also reported to be effective against Pa. chlamydospora, P. viticola and E. lata. Results
from bioassays on 1-year-old Chenin Blanc grapevine shoots indicated that benomyl,
tebuconazole and prochloraz manganese chloride were most effective in limiting lesion length in
pruning wounds that were inoculated with the Botryosphaeria spp after fungicide treatment. The
bioassay findings were, however, inconclusive due to low and varied re-isolation data of the
inoculated lesions. Benomyl, tebuconazole, prochloraz manganese chloride and flusilazole can
nonetheless be identified as fungicides to be evaluated as pruning wound protectants in
additional bioassays and vineyard trials against Botryosphaeria spp. as well as the other
grapevine trunk disease pathogens. / AFRIKAANSE OPSOMMING: Phaeomoniella chlamydospora, Eutypa lata, Phomopsis, Phaeoacremonium, en
Botryosphaeria spesies is die mees belangrikste stamsiekte patogene wat agteruitgang en vroeë
terugsterwing van wingerd veroorsaak. Voorafgaande navorsing het hoofsaaklik gefokus op
wyndruiwe en die voorkoms en simptomatologie van hierdie patogene op tafeldruiwe is dus
grootliks onbekend. ‘n Opname is gevolglik gedoen in verskillende klimaaatsareas waar
tafeldruiwe verbou word om die voorkoms en verspreiding, asook die simptome geassosieer met
hierdie patogene, te bepaal. Vyftien plase is geïdentifiseer in die winter- (De Doorns, Paarl en
Trawal) en somer-reënval (Upington en Groblersdal) streke. Wingerde (8 jaar en ouer) met die
kultivar Dan-ben-Hannah is gekies vir opname en monsters is gedurende Julie en Augustus 2004
geneem. Die distale deel van ‘n arm is verwyder vanaf 20 lukraak gekose plante in elke
wingerd. Hierdie dele is ontleed en isolasies is gemaak vanuit elke simptoomtipe wat beskryf is,
naamlik bruin en swart vaskulêre verkleuring, bruin interne nekrose, wig-vormige nekrose,
waterige nekrose, esca-geassosieerde bruin en geel sagte houtverrotting en asimptomatiese hout.
Identifikasie van die swamagtige isolate is gedoen op grond van morfologiese eienskappe en
molekulêre tegnieke. Pa. chlamydospora is die meeste geïsoleer (46.0%), gevolg deur
Phaeoacremonium aleophilum (10.0%), Phomopsis viticola (3.0%), Botryosphaeria obtusa
(3.0%), B. rhodina (2.2%), B. parva (2.0%), Fusicoccum vitifusiforme (0.6%), B. australis, B.
dothidea en ‘n onbeskryfde Diplodia sp. (0.2% elk), terwyl E. lata nie geïsoleer is nie. Hierdie
patogene is elk geïsoleer vanuit ‘n verskeidenheid simptoomtipes, wat daarop dui dat
siektediagnose nie alleenlik op simptomatologie gebaseer kan word nie. Pa. chlamydospora is
geïsoleer vanuit al die gebiede, alhoewel die patogeen opmerklik meer voorgekom het in die
winter-reënval area. Pm. aleophilum het hoofsaaklik voorgekom in Paarl, terwyl P. viticola
slegs in hierdie area voorgekom het. Alhoewel B. obtusa nie voorgekom het in die De Doorns en
Groblersdal areas nie, was dit die mees algemeen geïsoleerde Botryosphaeria sp. en het in
Upington, Paarl en Trawal voorgekom. B. rhodina het slegs in Groblersdal voorgekom, B. parva
in Paarl, Groblersdal en Trawal en B. australis het slegs in Paarl voorgekom. Die res van die isolate (33%) het bestaan uit steriele kulture, Exochalara, Cephalosporium, Wangiella,
Scytalidium, en Penicillium spesies asook twee onbekende basidiomycete isolate, geïsoleer
vanuit vyf monsters met geel eska-geassosieerde simptome vanuit die Paarl area. Hierdie
resultate illustreer dus die feit dat wingerdstamsiektes deur ‘n kompleks van swampatogene
veroorsaak word, wat belangrike implikasies het vir die bestuur en diagnose van hierdie siektes.
Wondbeskerming teen infeksie van enige van hierdie stamsiekte patogene is die mees
doeltreffende en koste-effektiewe manier om wingerdstamsiektes te voorkom. Vorige navorsing
aangaande die effektiwiteit van chemiese wondbeskermingsmiddels het egter slegs gefokus op
die beheer van Eutypa terugsterwing. In vitro swamdoder sensitiwiteitstoetse is gedoen vir Pa.
chlamydospora, P. viticola en Eutypa lata, maar geen studies is al gedoen ten opsigte van die
patogeniese Botryosphaeria spesies op wingerd in Suid-Afrika nie. Tien swamdoders is dus
getoets vir inhibisie van in vitro miseliumgroei van die vier mees algemene en/of patogeniese
Botryosphaeria spesies wat in Suid-Afrika voorkom, naamlik B. australis, B. obtusa, B. parva en
B. rhodina. Iprodione, pyrimethanil, koper ammonium asetaat, kresoxim-metiel en boscalid was
oneffektief by die hoogste konsentrasies getoets (5 μg/ml; 20 μg/ml vir koper ammonium
asetaat). Benomyl, tebuconasool, prochloraz mangaan chloried en flusilasool was die mees
effektiewe swamdoders met EC50 waardes tussen 0.36-0.55, 0.07-0.17, 0.07-1.15 en 0.04-0.36
μg/ml, onderskeidelik vir die verskillende spesies. Hierdie fungisiedes, behalwe prochloraz
mangaan chloried, is geregistreer op druiwe in Suid-Afrika en is ook effektief gevind teenoor Pa.
chlamydospora, P. viticola en E. lata. Resultate van biotoetse op 1-jaar-oue Chenin Blanc
wingerd lote het getoon dat benomyl, tebuconasool en prochloraz mangaan chloried die
effektiefste was om die lengte van letsels in snoeiwonde, geinokuleer met Botryosphaeria
spesies na die aanwending van swamdoder behandelings, te verminder. Die bevindinge was
egter onbeslis as gevolg van die lae en variërende her-isolerings data. Benomyl, tebuconasool,
prochloraz mangaan chloried en flusilasool kan egter geïdentifiseer word as swamdoders wat
verder geevalueer kan word as snoeiwond beskermingsmiddels teen Botryosphaeria spesies
asook ander wingerd stamsiekte patogene in verdere biotoetse en wingerdproewe.
|
3 |
The effect of different irrigation frequencies in combination with boron and calcium bunch applications on berry split of SoutherngrapeOneKoekemoer, Abraham Leander 03 1900 (has links)
Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The table grape industry employ a wide range of viticultural management
practices in order to produce the high quality grapes demanded by the export
market. A common contributor to degrading the quality of table grapes is the
occurrence of berry split, which not only has an unattractive visual effect, but
also increases the berries’ susceptibility to infection by spoilage organisms.
A number of environmental conditions such as rainfall and humidity, and/or
agricultural practices, such as irrigation, and high density canopies, can lead
to higher plant cell water content. This in turn, can increase the potential
of berry split to occur. To date, the main method of berry split prevention
has been the management of plant water status by; (i) regulating irrigation
withdrawal times, and (ii) covering of canopies if rainfall is predicted prior to
harvest. The aim of this study was to determine the effect that irrigation frequency,
as induced by irrigation withdrawals; as well as boron (B) and calcium (Ca)
treatments, applied as bunch directed sprays, have on pre- and post-harvest
berry split. To this end, a newly released late ripening, white seedless cultivar,
SoutherngrapeOne was chosen as a model cultivar as it has a high susceptibility
to berry split. SoutherngrapeOne vines were subsequently subjected to a range
of irrigation frequencies based on typical irrigation scheduling used in the table
grape industry, which comprised of a low, medium and high frequency. The
low frequency was duplicated in order to demonstrate the effect that a heavy
irrigation, just before harvest may have on berry split. These treatments were
further subdivided to investigate the effect that B and Ca may have on berry
split. For the B treatment, four Solubor1 bunch directed sprays were applied
from 8mm berry size to véraison. The Ca treatment consisted of Stopit R
2 and
Caltrac R
3 bunch directed sprays applied over the same period. In addition,
a combination of the B and Ca treatment were applied to investigate any
possible interaction. To account for the effect of water as solvent in the B
and Ca treatments, and the spraying effect, pure water as treatment was also
evaluated. Control vines received no sprays.
The applied irrigation treatments resulted in different plant water status
conditions. Separate applications of B and Ca treatments resulted in a decrease
of B and Ca content in the flesh respectively. The control and combination
treatment, of B and Ca resulted in the same of B and Ca content in the flesh.
Furthermore, none of the applied treatments resulted in an increase of either
B or Ca content in the berry skin.
It was found that the medium frequency irrigation resulted in the best
irrigation strategy to prevent pre-harvest berry split. Surprisingly, all the subtreatments:
B, Ca, and combination of B and Ca, resulted in an increased
incidence of pre-harvest berry split when compared to the control group for
the 2006/07 season. However, in the 2007/08 season only the B treatment
resulted in an increase of pre-harvest berry split.
Concerning post-cold-storage physiological disorders, Ca treatments appear
to have reduced berry drop, but increased decay. In the 2006/07 season,
the B treatment resulted in reduced post-cold-storage berry split, whereas Btreatment in the 2007/08 season had no effect. Both B and Ca should be considered
as having the potential to increase the appearance of hairline cracking.
Calcium treatment also led to an increase in decay which may have been as
a result of the splitting it contributed to. Low frequency irrigation recieving
irrigation before harvest was found to result in browner stems.
Low irrigation frequencies decreased the cell size of the berry skin. The Ca
treatment gave rise to thicker (weaker) cell walls, this morphological change
may be responsible for the physiological disorders it caused.
From these findings, it can be deduced that poorly managed irrigation,
together with unnecessary application of B and/or Ca may result in an increase
of berry split and other physiological disorders, with subsequent financial losses
for the producer. / AFRIKAANSE OPSOMMING; Die tafeldruifindustrie maak gebruik van ’n wye reeks wingerdkundige praktyke
ten einde die hoë gehalte druiwe te produseer wat die uitvoermark vereis.
Korrelbars is ’n algemene verskynsel wat afbreek maak tot die gehalte van tafeldruiwe.
Behalwe dat voorkoms van die druiwe benaadeel word, verhoog dit
ook in vatbaarheid vir infeksie deur verrottingsveroorsakende swamme. Hoë
reënval en humiditeit, sowel as wingerdkundige praktyke soos besproeiing en
hoë lowerdigtheid, wat kan lei tot verhoogde waterstatus in plante, kan lei tot
’n toename in korrelbars.
Daar word hoofsaaklik van twee metodes gebruik gemaak om korrelbars te
beheer, naamlik die bestuur van plantwaterstatus deur; (i) beheer van besproeiingsontrekkingstye
en (ii) bedekking van lowers indien reën voorspel
word voor oestyd. Die doel van hierdie studie was om vas te stel wat die invloed van besproeiings
frekwensies sowel as trosgerigte boor (B) en kalsium (Ca), spuitbehandelings,
op voor- en na-oes korrelbars het. Die onlangs vrygestelde laat
rypwordende, wit, pitlose kultivar, SoutherngrapeOne is gebruik, aangesien dit
hoogs gevoelig is vir korrelbars.
Stokke is aan verskillende besproeiings intervalle, soos tipies gebruiklik
in die tafeldruifindustrie, blootgestel. Hierdie intervalle bestaan uit n’ lae,
medium en hoë besproeiings frekwensie. Die lae besproeiings frekwensie is
herhaal ten einde die invloed van besproeiing net voor oestyd op korrelbars
te ondersoek. Die invloed van B- en Ca-behandeling op korrelbars is ook ondersoek.
Vir die B-behandeling is vier Solubor1 trosgerigte spuite aangewend
vanaf 8mm korrelgrootte tot deurslaan. Vir die Ca-behandeling is Stopit R
2
en Caltrac R
3 as trosgerigte spuite oor dieselfde tyd toegedien. Kombinasiebehandelings
is ook aangewend om enige interaksie tussen B en Ca te ondersoek.
Waterbehandelings is ook toegedien om die invloed van water as oplosmiddel
van B- en Ca-behandelings sowel as die spuit-effek te ondersoek. Kontrole
stokke is ook ingesluit en het geen spuitebehandeling ontvang nie.
Die besproeiingsbehandelings het verskillende plantwater toestande tot
gevolg gehad, B- en Ca-behandelings het gelei tot ’n afname in B- en Cainhoud
in die vleis onderskeidelik. Die kombinasie en kontrole behandelings
het eenderse hoeveelhede B en Ca in die vleis tot gevolg gehad. Geen van die
aangewende behandelings gelei tot ’n toename in B- en Ca-inhoud in die dop
nie.
Die resultate toon dat medium besproeiings frekwensie die beste besproeiingsstrategie
is om voor-oes korrelbars te voorkom. In vergelyking met die
kontrole-behandeling in 2006/07, het B, Ca en die kombinasie van B en Ca, ’n
toename in voor-oes korrelbars tot gevolg gehad. In die 2007/08 seisoen het
slegs die B-toediening egter tot ’n toename in voor-oes korrelbars gelei.
Kalsium behandelings het ’n afname in los-korrels, maar ’n verhoging in
korrelbars tot gevolg gehad. In 2006/07, het B-toediening tot ’n afname in
korrelbars na koelopberging gelei, maar in die 2007/08 seisoen het dit geen
effek gehad nie. Beide B- en Ca-toediening het die potensiaal om haarlyn
barste te veroorsaak. Kalsium toediening het bederf verhoog wat moontlik aan die hoër bars wat dit induseer toegeskryf kan word.
Lae besproeiings frekwensie, het bruiner stingels veroorsaak, en ook gelei
tot ’n afname van selgrootte in die dop. Die Ca-toediening het aanleiding gegee
tot dikker selwande in die dop. Hierdie anatomiese veranderinge kan moontlik
die rede wees vir die verhoging in fisiologise afwykings.
Van hierdie bevindinge kan ons aflei dat swak bestuur van besproeiing,
sowel as die onnodige aanwending van B en/of Ca, kan aanleiding gee tot ’n
toename in korrelbars en ander fisiologiese afwykings, en dus finansiële verliese
vir die produsent inhou.
|
4 |
Source and identity of insect contaminants in export consignments of table grapesPryke, James Stephen 03 1900 (has links)
Thesis (MScAgric (Conservation Ecology and Entomology)--University of Stellenbosch, 2005. / 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.
|
Page generated in 0.0853 seconds