The effects of neem of oil biopesticide and organic amendments on the performance of solanum lycopersium infestation of tuta absoluta in different soil types

Abstract

Tomato (Solanum lycopersicum) production in the Limpopo Vhembe district is increasingly constrained by Tuta absoluta, a destructive pest that causes intense yield losses, and by poor soil fertility. The extensive use of conventional chemicals to enhance yield and reduce damage is now considered unsustainable. In contrast, biopesticides and organic amendments offer a more environmentally friendly approach, while also improving nutrient availability to enhance crop performance. The study investigated the combined effects of neem oil biopesticide, poultry litter, and vermicompost on tomato performance, T. absoluta infestation, and soil properties across different soil types. A two-trial pot experiment was conducted at the University of Venda nursery during the Summer and Spring 2024 growing seasons. The experiment was conducted in an open wire structure nursery, exposing the plants to environmental factors such as sunlight, temperature, and rainfall. Supplementary irrigation was applied when necessary. Poultry litter and vermicompost were applied at (20 t/ha) once only at the start of the summer season, and were applied one week prior to transplanting. The Hutton and Augrabies soils and the organic amendments were initially analysed for their chemical properties, and the treatments were reanalysed after each trial. Neem oil was prepared at a 5% solution (10 L) and applied at early, active flowering, and fruiting stages. In three replications, the treatments were arranged in a randomised complete block design. Plant height and number of branches were measured from the vegetative stage to harvest, while root length, fruit number, fruit weight, and infested fruits were assessed at harvest. Infested leaves were assessed during the early flowering, active flowering, and fruiting stages. The data obtained were analysed using two-way factorial design of ANOVA (GLM) in Minitab version 19, with mean separation performed at P ≤ 0.05. The poultry litter + vermicompost and poultry litter + vermicompost + neem oil treatments significantly (P < 0.05) improved plant height and the number of branches at various growth stages in both seasons. The combined treatments strengthened the nutrient pool compared to individual organic amendments. The soil type significantly affected plant height and number of branches (P < 0.05), though responses varied across soil types. However, the Hutton clay soil positively affected the parameters due to its clay texture, which retains soil moisture, nutrients, and organic matter. Poultry litter + vermicompost significantly increased root length (P < 0.05) in the first trial; no significant effect was observed in the second trial. The soil type significantly affected root length (P < 0.05) in both trials; the root length response varied across soil types and seasons. In the first trial, the plants in Augrabies sandy soil showed improved root length, while in the second trial, the plants in Hutton soil showed improved root length. The high root length in plants grown in Augrabies sandy loam soil is due to a high phosphorus content (Initial chemical composition, which is strongly associated with root initiation and elongation. Other nutrients also contributed to increased root length in Hutton clay soil, as evidenced by improved P, K, Ca, and Zn levels, which supported elongation and metabolic processes involved in root development. Soil type and organic amendments had no substantial impact on fruit weight, fruit number, and number of damaged fruits in both seasons, due to high variability among treatments, rendering the results statistically insignificant. The treatment, poultry litter + vermicompost + neem oil, recorded the fewest infested leaves in both seasons, as the combined organic amendments enhanced plant defence mechanisms, complemented by the azadirachtin in neem oil, which was effective against T. absoluta. The Augrabies sandy loam soil also resulted in a few infested leaves and poor tomato performance in both seasons compared to the Hutton clay soil, due to its lower nutrient content, low moisture, and less stable structure, which led to poor plant performance and consequently reduced infestation. The summer season resulted in improved plant performance and lower infestation, while the spring season resulted in less improved plant performance and higher infestation, indicating that the summer season was the best. The results indicate that integrating poultry litter, vermicompost, and neem oil biopesticide is an environmentally friendly approach that enhances tomato growth and controls excessive infestations of T. absoluta, while limiting farmers’ dependence on chemical fertilisers and pesticides. Augrabies soil type resulted in less infestation in both seasons, and it is highly recommended to reconsider the reapplication of organic amendments in spring season, as the residues in this study did not improve tomato performance. It is highly recommended to plant tomatoes in summer due to favourable weather conditions, which improve plant performance and reduce infestation. Future research should evaluate this approach on a larger scale under different climatic and environmental conditions.