Selected Micronutrients Effects on Pest and Disease Resistance, Yield and Quality of Tomato in Bomet County, Kenya
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Date
2025-11
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Kenyatta University
Abstract
Tomato (Solanum lycopersicum L.) is an important horticultural crop in Kenya, widely grown for both household consumption and income generation. However, tomato production in Bomet County has been constrained by persistent arthropod pest infestations and diseases, as well as poor soil fertility characterized by micronutrient deficiencies. These challenges have led to increased reliance on chemical pesticides, which are costly and environmentally harmful. This study was conducted to evaluate the effects of selected micronutrients—copper (Cu) and zinc (Zn)—on pest and disease resistance, yield, and fruit quality of tomato varieties in Chepalungu Sub County, Bomet County, Kenya. Objectives of the study were to: (i) determine the prevalence of tomato diseases and arthropod pests (ii) assess the influence of foliar applied zinc and copper micronutrients on the incidence and severity of key tomato pests and diseases (iii) evaluate the antioxidant levels specifically vitamin C, beta carotene and vitamin K in three tomato varieties in relation to micronutrient application. A field survey was conducted among 100 tomato farmers to identify existing production practices, major pest and disease problems, and fertilizer use patterns. Field experiments were then established in a Randomized Complete Block Design (RCBD) with three replications with split plot arrangements. The main plots consisted of three tomato varieties (Cal-J, Rio Grande, and Royal Oxly), while the subplots consisted of micronutrient treatments: copper sulphate (CuSO4), zinc sulphate (ZnSO4), and their combination (Cu SO4+ ZnSO4), applied weekly as foliar sprays at 0.5% concentration beginning four weeks after transplanting until harvest. Data on arthropod pest infestation, disease incidence and severity, and yield components were collected through field observations and laboratory analyses. Vitamin C and beta-carotene levels were determined using High Performance Liquid Chromatography (HPLC). Data from the field survey were analysed using SPSS version 18.0, while experimental data were analysed using SAS version 9.4 under the General Linear Model (GLM), and treatment means separated using Least Significant Difference (LSD) at 5% probability level. Results indicated that Frankliniella occidentalis (thrips) and Tuta absoluta (tomato leaf miner) were the most prevalent pests, while late blight (Phytophthora infestans) and early blight (Alternaria solani) were the most widespread diseases. Application of zinc and copper micronutrients, either singly or in combination, significantly (p < 0.05) reduced pest infestation and disease incidence compared to untreated control plots. The combined treatment (CuSO4 + ZnSO4) elicited the highest vitamin C production and beta-carotene levels and led to the greatest marketable yield (up to 2.6 t ha⁻ ¹) in the Cal-J variety. The study concludes that zinc and copper micronutrients enhance tomato resistance to pests and diseases, improve fruit nutritional quality, and increase yield under field conditions in Bomet County. It recommends that farmers integrate foliar application of zinc and copper micronutrients at 0.5% concentration as part of sustainable tomato production practices to reduce chemical pesticide use and promote environmental and food safety.
Description
A Thesis Submitted in Partial Fulfilment of the Requirements for the Award of the Degree of Master of Science in Crop Protection (Pathology) in the School of Agriculture and Environmental Sciences, Kenyatta University, November 2025.
Supervisors
1. Dr. Namikoye E. Samita
2. Prof. Joseph P. Onyango Gweyi