Browsing by Author "Pringle, K. L."

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    Effects of Pesticides and Fungicides Used on Grapevines on the Mealybug Predatory Beetle Nephus 'boschianus' (Coccinellidae, Scymnini)
    (South African Society for Enology and Viticulture, 2001) Walton, V. M.; Pringle, K. L.
    The effects of frequently used grapevine insecticides and fungicides on adults of the predatory beetle Nephus 'boschianus' of vine mealybug, Planococcus ficus (Signoret), were determined under laboratory conditions. When applied as cover sprays the pesticides chlorpyrifos, endosulfan, cypermethrin, chlorfenapyr and mercaptothion were very toxic to the predator, whilst the fungicides penconazole, fosetyl-Al, mancozeb and an insecticidal soap plus oil mixture were harmless. These results suggest that the insecticides may be harmful to a biological control system where N. 'boschianus' populations were dominant during the season. The three fungicides and the soap plus oil mixture, however, should be compatible with biological control by N. 'boschianus'.
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    Effects of pesticides used on table grapes on the mealybug parasitoid coccidoxenoides peregrinus (timberlake) (hymenoptera : encyrtidae)
    (South African Society for Enology and Viticulture, 1999) Walton, V. M.; Pringle, K. L.
    The effects of regularly used table grape insecticides and fungicides on 1-day-old adults of the parasitoid Coccidoxenoides peregrinus (Timberlake) of vine mealybug, Planococcus ficus (Signoret), were determined in the laboratory. The insecticides chlorpyrifos, endosulfan and cypermethrin were highly toxic to the parasitoid, while the fungicides penconazole and mancozeb were not. These results suggest that the insecticides may be detrimental to a biological control system using C. peregrinus while the two fungicides tested should be compatible with augmentative releases of C. peregrinus.
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    Field evaluation of insecticides for the control of citrus thrips Scirtothrips aurantii (Thysanoptera: Thripidae), on mango
    (2000) Grove, T.; Giliomee, J. H.; Pringle, K. L.
    The South African citrus thrips, Scirtothrips aurantli, also infests mango (Mangifera indica), causing lesions and rendering the fruit unsuitable lor export. Several insecticides were evaluated in the field for the control of S. aurantiion mango fruit in the Mpumalanga Province of South Africa. The inseC1icides tested were formetanate, lormetanate + sugar, tartar emetic + sugar, methamidophos, sulphur, phenthoate, cypermethrin, fipronil, lenthion, isofenphos, prothiolos and an extract 01 syringa (Melia azedarach), A non-toxic, garlic-based insect repellent and feeding depressant was also evaluated. Best control was obtained with formetanate and lipronil. The garlic-based substance showed potential, but not the syringa extract.
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    Occurrence of fruit-decaying fungi on adult male Mediterranean fruit flies (ceratitis capitata) captured in orchards and adjacent vineyards
    (South African Journal of Enology & Viticulture, 2004) Engelbrecht, R.; Holz, G.; Pringle, K. L.
    The occurrence of adult male Ceratitis fruit flies and their potential to transmit fungi associated with pre- and postharvest decay of fruit in natura were investigated. Sensus fruit-fly traps were installed in orchards each bordering on a vineyard on farms in the Stellenbosch region, South Africa. Ceratitis fruit flies were collected weekly, identified and counted to determine the fluctuations in fruit-fly population levels. Captured fruit flies were plated on a semi-selective medium and the number of flies yielding the fungi was recorded. Both the Mediterranean fruit fly (C. capitata), and the Natal fruit fly (C. rosa) were trapped. C. rosa seldom occurred and comprised only 1 % of the total number of flies captured. Fruit-fly patterns showed that early infestation of orchards may contribute to the infestation of adjacent vineyards later in the season. At localities where flies were not trapped in the early season, infestation usually occurred in the orchards and adjacent vineyards in the late season, and well after fruits were harvested. Fruit flies from all localities yielded species of Alternaria, Penicillium, Aspergillus, Rhiwpus, Mucor and Botrytis cinerea on the medium. Of the different fungi, Alternaria and Penicillium spp. were most commonly carried by the flies at the various localities. The organisms occurred in a specific pattern on flies captured at a specific locality, and in a given orchard or vineyard. The pattern of fruit-fly infestation and their fungal contamination suggest that the Mediterranean Fruit-fly has the potential to transfer fungi associated with post-harvest decay in natura from early-season to mid- and late-season peach and plum orchards, and to neighbouring mid- and late-season wine and table grape vineyards. This highlights the importance of fruit-fly management in order to control disease epidemics in orchards and vineyards.
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    Postharvest disinfestation treatments for deciduous and citrus fruits of the Western Cape, South Africa : a database analysis
    (Academy of Science for South Africa, 2008) Pryke, J. S.; Pringle, K. L.
    EFFECTIVE POSTHARVEST DISINFESTATION of export fruits from the Western Cape province of South Africa would help to reduce rejections due to the presence of insects. However, there is normally only a limited opportunity between controlling the insects and damaging the produce. A widely used agent in disinfestation procedures, methyl bromide, was scheduled to be withdrawn in many countries in 2005 due to its ozone-depleting properties. The main alternatives are irradiation, extreme temperatures, forced air, vapour-heat methods and the use of controlled atmospheres. A literature survey was used to identify postharvest treatments with the highest likelihood of success in killing insect contaminants without damaging the fruit. Data from 284 scientific articles relating to these kinds of disinfestation were entered into a database (PQUAD). Queries were run to determine the most intensively studied fruits and pests. The tolerances of the commodities were compared with those of the pests at family level. Where pest tolerances were lower than those of the fruit, the treatment was regarded as a possible candidate for use. Methyl bromide, controlled atmospheres and irradiation were identified as the most widely used against pests. Irradiation appeared to control insects at doses that did not damage deciduous produce. Citrus appeared to be more susceptible to damage, however, than deciduous fruits. Low temperature also seemed to be less detrimental to deciduous fruit than to citrus. Deciduous fruit is already preserved in cold storage, making this an inexpensive option to combat insects. Cold treatment appeared to control members of the Pseudococcidae, Tephritidae and Tortricidae; more work is required on the other pest families. Controlled atmospheres also had a high chance of success for both citrus and deciduous fruits.
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    Resistance in uncinula necator to triazole fungicides in South African grapevines
    (South African Society for Enology and Viticulture, 2000) Halleen, F.; Holz, G.; Pringle, K. L.
    The distribution of Uncinula necator variants resistant to triadimenol, penconazole and flusilazole were determined in vineyards with suspected resistance in the regions Tulbagh, Franschhoek, Stellenbosch, De Dooms, Riebeeck Kasteel and Paarl. The regional subpopulations had all been exposed to triadimefon or triadimenol prior to 1989, when these fungicides were phased out and other demethylation-inhibiting fungicides (DMls) were applied. The occurrence of resistant variants in the subpopulations was compared with those in a vineyard in the Ceres Karoo region, which was isolated by two mountain ranges from the viticultural regions and where triadimefon was used prior to 1989, then abandoned. No other DMls were applied. A discriminatory germ tube length was used as a criterion to distinguish between sensitive and tolerant conidia at a discriminatory fungicide dose of 0.3 μg/mL. All the populations showed reduced sensitivity to triadimenol. This finding indicated an earlier shift in triadimenol sensitivity in the subpopulations and showed that resistant variants are sufficiently competitive to become established in vineyards. Cross-resistance between the triazoles was indicated by the frequency at which resistant variants occurred in subpopulations. The Ceres Karoo population was at baseline sensitivity level for penconazole and flusilazole. However, the four populations (De Dooms, Franschhoek, Riebeeck Kasteel and Stellenbosch) which showed the highest shifts in sensitivity to triadimenol, also displayed a high level of reduced sensitivity to flusilazole. This was in spite of the fact that only the Stellenbosch population was regularly treated with flusilazole. The other three populations were predominantly exposed to penconazole. Reduced sensitivity to penconazole was furthermore most prevalent in the Paarl K, Paarl I, Riebeeck Kasteel and De Dooms populations. Of these populations, Paarl K and Paarl I received predominantly penconazole, whereas the other two populations were treated with a range of DMis. Penconazole EDso values for the Paarl K, Paarl I, Riebeeck Kasteel and De Dooms pathogen populations (which showed the highest shifts in sensitivity to this fungicide) were 0.908, 1.022, 1.253 and 1.942 μg/mL, respectively. In these populations, 53%, 38%, 71 % and 91 % of the conidia respectively belonged to the 1.0-3.0 μg/mL and higher resistant classes. Reduced sensitivity to flusilazole was most prevalent in the Stellenbosch, De Doorns, Riebeeck Kasteel and Franschhoek populations. Flusilazole EDso values for these populations were 1.580, 1.813, 2.143, 3.885 μg/mL, respectively, whereas 83%, 82%, 96% and 79% of the conidia respectively belonged to the 1.0-3.0 μg/mL and higher resistant classes. These findings suggest a differing sensitivity of the pathogen to the three triazole fungicides which indicate that resistance to DMis is a multigenic trait in U. necator.
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    A sampling system for estimating population levels of the citrus thrips, Scirtothrips aurantii Faure (Thysanoptera: Thripidae) in mango orchards
    (2000) Grove, T.; Pringle, K. L.
    Data were collected over a two-year period at four localities in Mpumalanga Province, South Africa, to formulate a sampling technique for monitoring population levels of the citrus thrips, Scirtothrips aurantii Faure, in mango orchards. Using a two-stage sampling system for determining population levels, the optimum combination of the number of trees per orchard (primary units) and fruit per tree (secondary units), was estimated. Taylor's power law regression of log(S2) on 10g(X. . ) provided a good fit for both the within-tree (r-2 = 0.887) and between-tree (r-2 0.746) data. The value for the aggregation coefficient, b, in both cases was>1, indicating a dumped distribution. Sampling precision, D, improved with increasing average numbers of S. aurantii pedruit. ln addition, keeping the total number of fruit examined constant, sampling precision at low population levels improved by increasing the number of trees sampled and decreasing the number of fruit examined per tree. Examining 50 fruit per orchard should be sufficient for obtaining suitably accurate population estimates for pest management purposes.
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    Science and advocacy : the GM debate in South Africa
    (Academy of Science for South Africa, 2005) McGeoch, M. A.; Pringle, K. L.
    SOUTH AFRICA HAS AN EFFECTIVE regulatory framework for transgenics, and its rate of adopting genetic modification technology is amongst the highest in the world. However, the ecological consequences of introducing genetically modified organisms in this country have not been systematically explored. It is critical to do so if we are to continue to make informed choices on the extent to which the technology should be adopted.
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    A survey of mealybugs and associated natural enemies in vineyards in the Western Cape Province, South Africa
    (South African Journal of Enology & Viticulture, 2004) Walton, V. M.; Pringle, K. L.
    A survey of mealybugs and their associated natural enemies occurring in vineyards was conducted in the Western Cape Province during the 1999/2000 and 2000/2001 seasons. Planococcus ficus (Signoret) was the dominant mealybug and was found for the first time on roots of grapevines. This has far-reaching implications for the control of this important vine leafroll virus vector as control measures have been focused on above-ground control. Other mealybugs recorded on vines were Pseudococcus longispinus (Targioni-Tozzetti) and Ferrisia malvastra (McDaniel). Pseudococcus viburni (Maskell) and Ps. solani Ferris were found on weeds in vineyards. The more frequently recorded natural enemies of P. ficus were species of Nephus predatory beetles and the parasitoids, Coccidoxenoides perminutus Girault, Anagyrus sp. and Leptomastix dactylopii (Howard).
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    Treatment levels for citrus thrips, Scirtothrips aurantii (Thysanoptera: Thripidae), in mango orchards
    (2000) Grove, T.; Giliomee, J. H.; Pringle, K. L.
    ENGLISH ABSTRACT: Field work was carried out at three different sites in the Mpumalanga Province of South Africa to determine the correlation between the numbers of citrus thrips, Scirtothrlps aurantii, and the damage caused on mango. Adults of S. aurantiiwere monitored weekly by means of yellow sticky traps, while fruit was inspected visually and the number of adults and larvae recorded. Percentage fruit unacceptable lor export was determined at harvesting. Cumulative insect-days computed for S. aurantii on the traps and fruit were correlated with the percentage fruit showing lesions exceeding the level acceptable for export. The relationship between the number of S. aurantiion traps (cumulative insect-days) and the percentage fruit culled was described by Y 0 + 0.OO2X, while the number on fruit was described by Y = 0 + 0.21 Ox. To maintain the percentage culled fruit at a 5 % or lower level, producers should implement chemical intervention when the number of S. aurantii exceeds 2326 cumulative insect-days on traps, or 24 days on fruit.
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    The use of economic thresholds in pest management : apples in South Africa
    (Academy of Science for South Africa, 2006) Pringle, K. L.
    MONITORING SYSTEMS AND ECONOMIC thresholds can be used to determine the necessity for and timing of measures to control herbivorous arthropods which attack agricultural crops, particularly high-value ones such as apples. The data obtained from these monitoring systems, however, have far wider applications than just determining whether or not control measures are required. They can be used to decide the pest status of herbivorous arthropods, whether or not sporadic pests require attention during a particular season, to refine the timing of actions against perennial pests and to determine the effectiveness of measures applied to control chronic pests. Optimum use of monitoring data can help local exporters to supply unblemished fruit with the minimum use of insecticides to South Africa's main foreign markets, the European Union and the United States.
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    Vine mealybug, planococcus ficus (signoret) (hemiptera: pseudococcidae), a key pest in South African vineyards. a review
    (South African Society for Enology and Viticulture, 2004) Walton, V. M.; Pringle, K. L.
    Vine mealybug, Planococcus ficus (Signoret), is a key pest in vineyards in the Western Cape and North-West Provinces of South Africa and more recently in the USA. This pest was first reported in the Western Cape Province in 1943. The taxonomy and identification of this species are made difficult by complex slide-mounting techniques and the lack of qualitative characteristics. Vine mealybug is polyphagous with a wide range of host plants. P. ficus causes direct crop loss due to desiccation of bunches in the case of wine grapes and unsightly honeydew excretion on bunches in the case of table grapes. High infestations of P. ficus can cause early leaf loss and resultant weakening of vines. Vine mealybug also vectors the vine leafroll virus. This pest is currently controlled using chemical, biological and cultural control techniques in an integrated pest-management system. This system relies on the use of pheromone and physical monitoring techniques, which provide information on infestation levels.