Browsing by Author "Vermaak, Mia"

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    The diversity and ecology of mites (acari) in vineyards
    (Stellenbosch : Stellenbosch University, 2019-03) Vermaak, Mia; Addison, Pia; Veldtman, Ruan; Ueckermann, Eddie; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: The common grapevine (Vitis vinifera L.) is the main species used for wine making, with South Africa being one of the top wine exporting countries. Grapevine is vulnerable to a range of pests, one of these being mites. Plant-parasitic mites are extremely damaging pests with a rapid generation time, high fecundity and a tendency to over-exploit their hosts. Disconcertingly, the diversity of mites in vineyards in South Africa is virtually unknown. Surveys have been done with predatory mites and phytophagous mites being recorded, but no recent studies focussing on their ecology, pest status and seasonal cycles have been collected. The aim of this study was to survey phytophagous and predatory mite diversity and to investigate pest status of the plant feeding mites of South African grapevine, including the recently introduced, invasive Brevipalpus lewisi. Sampling was done over a two-year period and included four conventional farms and one organic farm found in the Winelands region of the south Western Cape, South Africa. Each conventional farm contained a motherblock, nursery and commercial vineyard while the organic vineyard only consisted of a commercial vineyard. At each site vine branches were collected on a regular basis from November 2016 to April 2018. During the winter months weed and cover crop samples were also collected at the conventional farms. Mites were collected from vine leaves with a mite brushing machine. Weeds and cover crops were inspected with a microscope and mites were collected from them with a fine brush. Mites were slide mounted and identified. The predatory mite diversity from plant samples was much higher than expected. Eueseius addoensis and Typhlodromus praeacutus were the most abundant predatory mites found in the commercial vineyards and nursery material with T. praeacutus and Neoseiulus barkeri the most common in motherblocks. Brevipalpus species were the abundant phytophagous mites, with Tetranychidae being less abundant. Brevipalpus lewisi was the most dominant species. It did not cause any visual symptoms of damage on the vine. Brevipalpus lewisi did not seem to have natural enemies that were at sufficient densities to affect any control. The seasonal cycles for the predatory and phytophagous mites were established over a period of two seasons; from November 2016 to May 2017 and from November 2017 to April 2018. In commercial vineyards E. addoensis and T. praeacutus were the only predatory mites that were present throughout the entire season. The other predators were present for one or two months. Motherblocks and nurseries had sporadic occurrences of predators. In all three vineyard blocks B. lewisi was dominant throughout the seasons. The organic vineyard survey showed a high diversity of predatory mites and an absence of plant-feeding mites. The dominant predators were also E. addoensis and Typhlodromus saevus. In this study it was found that the main grapevine mites did not migrate to alternate hosts like the cover crops and weeds during winter. Mites that were found on both ground cover and vines were Tydeus grabouwi and Tetranychus ludeni. The findings of this study forms baseline data to develop management strategies to be used in the wine industry. Understanding the diversity and seasonal cycles of the mites occurring on grapevine will make for better decision making in pest control.