An Investigation on the Effects of Pepper-Bark Plant (Warburgia Salutaris) Leaf Extracts, as a Potential Organic Fungicide for Tomato Crop Protection by Small Holder Farmers

Abstract

This study investigated the efficacy of Warburgia salutaris (pepper-bark) leaf extracts as an organic fungicide for controlling foliar fungal diseases in tomato crops (Solanum lycopersicum cv. ‘Jemar’). The experiment was conducted at Mutare Polytechnic, Zimbabwe, in 2024, using a Randomised Complete Block Design (RCBD) with five treatments and five replications. Treatments comprised three extract concentrations (5%, 10%, and 15%), a commercial fungicide (Bravo® 500 SC), and an untreated control. Results showed significant differences among treatments (p ≤ 0.001) for all measured variables. The 10% and 15% concentrations achieved mean disease severity ratings of 1.5 ± 0.2 and 1.2 ± 0.1 respectively, representing Alternaria solani disease reductions of 66.7% and 73.3% relative to the untreated control (4.5 ± 0.5), and were statistically comparable to Bravo (1.8 ± 0.2). The 15% concentration produced the highest fruit yield (3.3 ± 0.2 kg/plant) and fruit count (13.1 ± 1.2 fruits/plant), exceeding Bravo in both A. solani disease control (122%) and yield performance (118%). A strong negative correlation was observed between disease severity and fruit weight (r = −0.89, p ≤ 0.001). These findings demonstrate preliminary evidence that W. salutaris leaf extract, particularly at 10–15% concentrations, is an effective and practical organic fungicide option for smallholder tomato farmers, comparable to or exceeding the performance of a conventional synthetic fungicide under field conditions.