Digital Knowledge Collection:

The insecticidal and repellent activities of extracts of three Allium spp. (Amaryllidaceae) against grapevine mealybug (Planococcus ficus L.)

Thu, 01 Jan 2026 00:00:00 GMT

Title: The insecticidal and repellent activities of extracts of three Allium spp. (Amaryllidaceae) against grapevine mealybug (Planococcus ficus L.) Authors: Mange, Tokozani Abstract: Grapevines are susceptible to a wide variety of pests, including the grapevine mealybug. It is one of the most economically important pests of wine grapes. It causes sooty moulds on grape clusters and transmits the grapevine leafroll-associated virus. One of the primary methods for controlling this pest in the vineyard is the application of synthetic insecticides. However, these synthetic insecticides harm natural enemies, the environment, and human health. In modern agriculture, Plants are increasingly being recognised as an important source of insecticides. Many plant-based insecticides are used as alternatives to reduce the reliance on chemical insecticides. Hence, researchers have been developing new and safer pest control methods. Plant-based insecticides have been traditionally used worldwide, particularly by subsistence/smallholders. Allium species are among the most extensively researched plants for their sulphur compounds and other bioactive compounds. The first part of this study, in Chapter One, begins with the background and rationale of the study, followed by a systematic literature review in Chapter Two, focusing on the use of plantbased products screened for pest repellence and insecticidal properties against the vine mealybug, which revealed that several plant species from different families have insecticidal properties against the vine mealybug pests. Chapter 3 is the experimental part of this study, consisting of two bioassays: toxicity and repellency, which evaluated the toxicity of Allium species (A. sativum, A. cepa, and A. porrum) against the vine mealybug. The three Allium spp. were store-bought, the garlic and onion were peeled, and the leek was rinsed and dried with a paper towel. The plants were crushed to a paste-like consistency and dissolved in various solvents (DCM, absolute ethanol, Acetone, and Distilled water) at room temperature (25 ℃) for 24 hours. The extracts were filtered and allowed to dry at room temperature (25 ℃). To perform the toxicity bioassay, the extracts were re-dissolved in extra-virgin olive oil to obtain a 25% w/v concentration, and this mixture was vortexed for 10 minutes. Fifty microlitres of each 25% w/v extract was applied to a 2x2 cm packet filter paper and allowed to dry for 5 minutes. A camel-hair brush was used to transfer the insect into the packet, and all sides were stapled. Five packets, each containing one insect, were placed in a petri dish and stored in a Perspex box containing saturated sodium solution in a 100 mL glass beaker, in a darkroom at room temperature and 60% RH. Data was collected after 10 minutes. The results showed a significant difference in insecticidal efficacy among the plant species (DF=2; P < 0.05). Garlic exhibited the highest potency against vine mealybug, particularly when extracted with DCM. The results showed that the DCM garlic extract was significantly more toxic (DF = 3; χ 2 = 23.09; P < 0.05), inducing 92% insect mortality at a concentration of 25% w/v. The DCM extract of garlic was further tested at different concentrations (25% w/v, 12.5% w/v, 6.25% w/v, 3.125% w/v) and at 0% (negative control) and compared to extra virgin olive oil. The highest corrected mortality rate was 92% of the vine mealybug, achieved at 25% w/v concentration. The mortality rate was concentration-dependent. The choice repellence bioassay evaluated the repellent activity of Allium spp. (garlic, onion, and leek) against the vine mealybug. The same plant preparation method was followed as for the toxicity experiment, except that the extracts were redissolved in solvents (DCM, Acetone, absolute ethanol, and Distilled water) to achieve a 25% w/v concentration and tested in a choice repellence bioassay. The results showed a significant difference in repellent efficacy. The acetone garlic extract was significantly more repellent than the other treatments (DF = 3; χ 2 = 19.95; P < 0.05). The distilled water extract of garlic and the organic soap exhibited 42% and 38% repellency, respectively, at 25% w/v. These findings demonstrated that garlic extracts have anti-grapevine mealybug activity and could be incorporated into integrated pest management. Description: Thesis (MAgric)--Cape Peninsula University of Technology, 2026

Oviposition and feeding preferences of the groundnut leaf miner (Bilobata subsecivella, Lepidoptera: Gelechiidae) on selected host plants under controlled environmental conditions

Thu, 01 Jan 2026 00:00:00 GMT

Title: Oviposition and feeding preferences of the groundnut leaf miner (Bilobata subsecivella, Lepidoptera: Gelechiidae) on selected host plants under controlled environmental conditions Authors: Ndimande, Muhle Pretty Abstract: The groundnut leaf miner (GLM), Bilobata subsecivella, is a highly destructive pest of legume crops, particularly groundnut (Arachis hypogaea) and soybean (Glycine max), but it also infests wild species such as hairy indigo (Indigofera hirsuta). However, little is known about how its behavioural preferences influence its spatial distribution and population dynamics. Such information is crucial for informing effective pest control measures, especially within the framework of Integrated Pest Management (IPM), which emphasises ecological understanding as the foundation for sustainable control strategies. This study compared infestation levels of GLM on groundnut, soybean, and hairy indigo; evaluated female GLM oviposition preferences among these three plants; and determined the preferred host plant for GLM larval feeding, using non-choice, twochoice, and three-choice assays. Results showed that all three host plants were suitable hosts for GLM feeding, though the intensity and mining patterns varied. Groundnut displayed broader blotch mines, hairy indigo had primarily linear mines, and soybean displayed intermediate characteristics. Oviposition trials revealed that soybean was the most preferred host for egg laying; however, it did not support successful larval development due to early defoliation. In contrast, groundnut was the most suitable host for infestation and larval performance. Hairy indigo, though least preferred for oviposition, supported larval development and was the only host on which adult emergence occurred in the second infestation trial. These findings highlight a significant mismatch between oviposition preference and larval performance, underscoring the importance of considering both host selection and developmental success when evaluating host suitability. The observed differences in feeding, oviposition and infestation patterns suggest that host plant suitability is strongly influenced by chemical, structural, and defensive traits. Future research should focus on identifying the specific cues driving oviposition and feeding intensity, as this knowledge could guide sustainable management strategies for GLM in legume cropping systems. Description: Thesis (MAgric)--Cape Peninsula University of Technology, 2026

Impact of activated water treatments and packaging systems on physiological responses, phytonutrients and overall quality of minimally processed Swiss chard (Beta vulgaris L.)

Thu, 01 Jan 2026 00:00:00 GMT

Title: Impact of activated water treatments and packaging systems on physiological responses, phytonutrients and overall quality of minimally processed Swiss chard (Beta vulgaris L.) Authors: Masilela, Ayanda Gift Abstract: Swiss chard is highly susceptible to postharvest handling practices that compromise its physicochemical quality and significantly reduce its shelf life, despite its richness in essential nutrients and health promoting compounds. Similar to other fresh-cut leafy vegetables (FCLVs), Swiss chard is prone to oxidative stress, microbial contamination, and physiological degradation during storage. To mitigate these challenges, postharvest sanitisation treatments, particularly those that contain oxidising and chlorine-based agents have been widely applied to preserve the nutritional value and overall quality of both whole and FCLVs. However, growing scientific evidence regarding the environmental persistence and health risks associated with synthetic chemical sanitisers have driven a global transition toward safer, eco-friendly alternatives. Among these, non-thermal activated water treatments, such as micro-nano bubble (MNB) technologies, have gained attention for their antimicrobial efficacy and broad applications across agricultural and food sectors. The aim of this study was to investigate the impact of MNB water technology and packaging systems on the overall quality, physiological responses, phytonutrients and microbial quality of minimally processed Swiss chard. MNB systems, namely air-generated MNB water and ozone micro-nanobubble (O3-MNBs), were evaluated for their effectiveness in improving post-harvest quality and storage stability of Swiss chard (cv. Fordhook Giant). Two experiments were conducted under identical storage conditions (5 °C) with samples packaged in BOPP films. In the first experiment, whole Swiss chard was treated for 10-min with air-MNB and compared against conventional sodium hypochlorite (NaOCl) and tap water (TW) over an 8-day storage period. In the second experiment, fresh-cut Swiss chard was treated with O3-MNBs and tap water for 5, 10, and 15 min, followed by storage for 15 days. The potential of air-MNBs as an alternative for conventional chlorine-based washing methods in leafy vegetables was investigated. The study examined the physiological responses, as well as the physicochemical and microbiological qualities, of packaged whole Swiss chard leaves. Results showed that air-MNB treatment significantly preserved chlorophyll contents, minimised moisture loss, and maintained leaf colouration better than both NaOCl and TW (p ≤ 0.05). Additionally, air-MNBs achieved a comparable ≤ 1-log reduction in aerobic mesophilic bacteria counts to that of NaOCl. At the end of storage duration, treatment with air-MNBs resulted in better visual quality compared to the control samples. To further elucidate the influence of activated water systems on the postharvest quality of minimally processed leafy vegetables, O3-MNB water was applied to fresh-cut Swiss chard (cv. Fordhook Giant). Fresh-cut Swiss chard pre-treated with O₃-MNBs exhibited significantly lower weight loss compared to those pre-treated with tap water treatments (p ≤ 0.05). In addition, O3-MNBs preserved leaf colour, and suppressed ethylene production relative to tap water. All the O₃-MNB treatments resulted in a decrease of total soluble solids and titratable acidity, however they were better retained in control tap water pre-treated samples (p ≤ 0.05). Notably, O₃-MNB-treated samples stimulated an early storage increase in phenolic content and induced the formation of new volatile compounds such as 1- Pentanol, associated with improved sensory attributes. Microbial analyses revealed that O₃-MNB treatments significantly reduced the populations of aerobic mesophilic bacteria, yeasts and moulds, with the 10-min exposure achieving the greatest microbial inhibition throughout storage and resulted in ≈ 1.6 Log reduction in total aerobic mesophilic bacteria and ≤ 1 Log reduction for yeast and moulds. Collectively, these findings underscore the potential of micro-nanobubble technology as an innovative, environmentally friendly postharvest intervention. By providing strong antimicrobial activity without the environmental and toxicological drawbacks of synthetic chemicals, MNB treatments effectively mitigate physiological deterioration while maintaining the sensory and nutritional integrity of leafy vegetables. Description: Thesis (MAgric)--Cape Peninsula University of Technology, 2026

Effect of different nitrogen sources and growth media on water use of blueberry cultivated under shade net

Thu, 01 Jan 2026 00:00:00 GMT

Title: Effect of different nitrogen sources and growth media on water use of blueberry cultivated under shade net Authors: Mshweshwe, Asemahle Abstract: Globally blueberry (Vaccinium spp.) production has rapidly increased in recent years, driven by consumers' increased demand for this nutritious fruit. This study investigated the interactive effects of different N sources and soilless growth media on water use, growth, yield, and quality of blueberry. A pot experiment was carried out in polythene bags under a white shade net. Three nitrogen sources: ammonium sulphate [(NH4)2SO4] (N 21.1%), calcium nitrate [Ca (NO3)2] (N 16.6%), and urea (H2NCONH2) (N 46%) were applied to two soilless substrates growth media (100% coir and a combination of 80% coir: 20% zeolite) in a randomized complete block design. Growth, fruit yield, and berry quality parameters were measured. Our results showed that treatment with NH4 + and 100% coir yielded higher values for most growth parameters, chlorophyll content index, proanthocyanidin, as well as the availability of macro and micronutrients in the soilless substrate. The 100% coir treatment favours early shoot expansion due to superaeration and root expansion, and the addition of zeolite to coir reduced water demand by the test plants. The retention of NH4 + by the 20% zeolite treatment was not beneficial to the blueberry plants, hindering chlorophyll content accumulation and photosynthesis. These results suggest that a further investigation into the influence of different zeolite levels on blueberry production cultivated using pots. The application of NH4 + enhances fruit size and weight, primarily by enhancing the process of photosynthesis through higher N and chlorophyll content in leaves, and ultimately improving nutrient assimilation and nutrient use efficiency. Description: Thesis (MAgric)--Cape Peninsula University of Technology, 2026