Browsing by Author "Grove, Tertia"

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    Thrips management in mango orchards
    (Stellenbosch : Stellenbosch University, 1999-03) Grove, Tertia; Giliomee, J. H.; Pringle, K. L.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology & Entomology.
    ENGLISH ABSTRACT: Thrips associated with mango trees {Mangifera indica L. (Anacardiaceae)} were collected over a five year period in the main mango production areas of South Africa. Fifteen species were identified, eleven belonging to the family Thripidae and four to the family Phlaeothripidae. The citrus thrips, Scirtothrips aurantii Faure and the red banded thrips, Selenothrips rubrocinctus (Giard) were the only two species found to cause lesions on the fruit. Scirtothrips aurantii was the economically most important species found. There was a tendency for lesions caused by S. aurantii to decrease in prominence as the fruit matured. Some lesions that were prominent at the beginning of the season appeared less clearly defined at the end of the season. However, badly marked fruit did not recover to the extent that it could be exported. Sticky traps (140mm X 76mm X O.2mm) of various colours were tested in mango orchards for the attraction of S. aurantii adults'. Yellow was superior to blue, white, red and green. Yellow traps can be used effectively for assessing activity levels of S. aurantii in mango orchards. Cumulative insect-days were computed for S. aurantii on the traps and on the fruit and were correlated with the percentage fruit with lesions making it unacceptable for export. Fruit with such lesions should not exceed 5%. Chemical intervention should be used when S. aurantii on the traps exceed 2326 cumulative insect-days and when numbers on the fruit exceed 24 cumulative insect-days. By using a two stage sampling system for determining S. aurantii population levels in mango orchards, the optimum combination of the number of trees per orchard (primaryunits) and fruit per tree (secondary units) was estimated. The recommendation is to sample 5 fruit from 10 trees. Hoerl's function (Y = aXbecX) was used to describe the relationship between the number of S. aurantii on the fruit and fruit size, as well the number on the traps and fruit size. Fruit size when the maximum numbers of S. aurantii occurred ranged from 20.22mm to 40.33mm, while the ·fruit size at maximum numbers on the traps was from 2.94mm to 36.82mm. Therefore, for the management of thrips S. aurantii it is essential that they are monitored until fruit are at least 40mm in length. Scirtothrips aurantii numbers started to build up during September which is the end of the flowering period and reached a peak usually during October or November when small fruit were present. Scirtothrips aurantii was only present on the fruit for a short period and the population survived on new growth that was present throughout the year. Low numbers were present from June until August. The highest number of S. aurantii was observed on the cultivar Sensation. Different insecticides were evaluated in the field· for control of S. aurantii on mango fruit. The insecticides tested were formetanate, formetanate plus sugar, tartar emetic plus sugar, methamidophos, sulphur, phenthoate, cypermethrin, fipronil, fenthion, isophenfos and prothiofos and an extract of Syringa [Melia azedarach L. (Meliaceae)]. A non-toxic, garlic based insect repellent and feeding depressant was also evaluated. The best control was obtained with formetanate and fipronil. The garlic based substance showed potential, but not the Syringa extract.