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Seedling production under smallholder farming systems can be negatively affected by both abiotic and biotic factors. Seedling damping-off caused by Rhizoctonia solani is one of the major biotic factors which causes significant yield reduction. Management is mainly based on the application of synthetic fungicides and cultural practices. However, both methods have limitations which result in their inefficiency. Several studies have reported on the use of plant extracts and biological control to manage plant diseases. The aim of this study was to formulate an effective and practical approach to manage tomato seedling dampingoff using extracts of Monsonia burkeana and Moringa oleifera and a biological control agent Trichoderma harzianum. The efficacy of both extracts was investigated under laboratory conditions to determine the most suppressive concentration to R. solani growth. Methanolic extracts from both plants significantly suppressed pathogen growth at different concentrations. M. burkeana significantly reduced R. solani growth at 8 g/mL (71%) relative to control whilst Moringa oleifera extract reduced pathogen growth by 60% at a concentration of 6 g/mL. The highest suppressive concentrations were further evaluated under greenhouse conditions to test their efficacy on seedling damping-off. In damping-off treatments, both plant extracts and T. harzianum also significantly reduced (p=0.5) pre- and post-emergence dampingoff incidence. M. burkeana recorded the highest suppression at 78%, followed by M. oleifera at 64%. Trichoderma harzianum reduced incidence of damping-off by 60% and this was higher than both plant extract treatments.

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Citrus black spot (CBS) caused by Phyllosticta citricarpa (McAlpine) Van der Aa (asexual state) synonym Guignardia citricarpa Kiely (sexual state) is one of the most devastating diseases of citrus which occurs in various citrus producing areas around the globe. Management is mainly based on monthly applications of copper fungicides and strobilurins under field conditions. In this study, biocontrol agents were evaluated as alternative post-harvest treatments against citrus black spot disease. Two bio-control agents namely, Bacillus subtilis Cohn and Trichoderma harzianum Rifai were evaluated for their efficacy against P. citricarpa. Their efficacy was further compared with commercial fungicides Dithane 750 (Mancozeb, 750 g/kg). Results obtained showed that T. harzianum treatments were highly suppressive towards pathogen growth in vitro (85%) as compared to B. subtillis (4%) and Dithane 750 (12%). Treatment of artificially inoculated fruits with combined formulations of both biocontrol agents resulted in reduced CBS severity as compared to their single applications. These findings suggest that T. harzianum had highest suppression of pathogen growth as compared to B. subtilis. The results also suggest that their combined application can provide an effective disease management when compared to sole application of Dithane 750. Further studies are however, needed to determine their effectiveness under field conditions and also their efficacy can be sustained when applied with commercial fungicides.