Browsing by Author "Fourie, Louis Welricht"

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    Investigating the use of Marigolds (Tagetes spp.) and brassicaceous cover crops as a tool for the management of lesion nematodes (Pratylenchus spp.) in apple orchards
    (Stellenbosch : Stellenbosch University, 2024-03) Fourie, Louis Welricht; Knoetze, Rinus; Stokwe, Nomakholwa Faith; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: The global surge in conscious consumerism favouring organically grown produce with minimal environmental impact has placed a considerable strain on global agriculture, particularly in fruit production which is heavily reliant on agrochemicals in crop protection programs. Fruit producers are expected to withdraw agrochemicals from crop protection programs to meet the demand for organically grown produce. Additionally, increasingly stringent maximum residue levels (MRLs) set by global export markets on agrochemical residue intensify the need for alternative crop protection solutions. Motivated by the drive towards organic produce, in this study, we evaluated the use of cover crops as an alternative control measure to chemical soil fumigation and the use of nematicides against the most prevalent nematode pest in South African apple orchards – the root lesion nematode (RLN) (Pratylenchus hippeastri). Two marigolds (Tagetes spp.) the African marigold (T. erecta) and the French marigold (T. patula) and three brassicaceous cover crops, brown mustard (Brassica juncea), Ethiopian mustard (Brassica carinata) and white mustard (Sinapis alba) were tested, through pot trials, for their ability to suppress RLN in infested orchard soil and inside the roots of infested apple trees. The suppressive potential of these cover crops was tested in three ways; (1) grown as a cover crop, (2) used as a soil amendment for biofumigation and (3) used as a soil amendment in combination with soil solarization (biodisinfestation). Along with this, a pilot trial was performed in a commercial apple orchard in Grabouw, Western Cape, South Africa (SA), where we evaluated the potential of marigolds to establish, grow, and suppress RLN in the soil and in the roots of apple trees under the conditions of a commercial apple orchard. Five inoculation methods were tried to obtain soil infested with RLN. Infested orchard soil in combination with infested apple root fragments proved to be most effective. However, this study emphasizes the need for an optimal growth medium which supports RLN survival while maintaining sterility for accurate experimental results. Cover crops used in these experiments are not conducive hosts to RLN. Marigolds, acting as cover crops, effectively reduce RLN populations in the soil through the release of an allelopathic root exudate, α-terthienyl. Conversely, brassicaceous cover crops do not impact RLN populations unless utilized for biofumigation. Biodisinfestation exhibits an enhanced level of RLN control in the soil as well as inside the apple roots consequently suppressing overall RLN reproduction. The success of biofumigation and biodisinfestation greatly depends on conducive climatic conditions (Adequate soil moisture, sufficient oxygen, and soil temperatures between 25°C – 35°C). Marigolds have the potential to serve as RLN-suppressing cover crops in commercial apple orchards. This study provides comprehensive evidence supporting the use of these cover crops as a tool for RLN management in apple orchards.