## 1 Introduction  
Maize (_Zea mays_ L.), which is the third most important crop across the world and the most significant grain crop in South Africa, is grown in diverse environments in the country [1, 2]. Despite its importance, the crop is ravaged by a number of pathogenic microorganisms ranging from bacteria, fungi and viruses among others, which causes a diverse range of diseases that challenge plant health and reduce both the quantity and quality of the yield at harvest [3, 4]. Among these disease-causing organisms, fungi occupy an important category owing to their short latent period, ease of spore dispersal and ability to sporulate prolifically and provide copious inoculum that could further infect plants [5]. Furthermore, their ability to infect a particular plant species is dependent on genes that differentiate the virulent fungi from their closely related nonvirulent relatives [6]. Fungi have been documented for their host specificity to maize and for causing diverse kinds of diseases such as ear and stalk rot caused by _Fusarium verticillides_[7], anthracose stalk rot (_Colletotrichum graminicola_), _Apergillus_ ear and kernel rot (_Aspergillus flavus_), charcoal rot of maize (_Macrophomina phaseolina_), corn grey leaf spot disease (_Cercospora zea-maydis_), southern corn leaf blight disease (_Bipolaris maydis_) and corn smut (_Ustilago maydis_) [8; 9; 10; 11; 12; 13]. Foliar fungal pathogens of maize have been reported to cause major yield losses in maize fields across South Africa. Some of these include common rust, northern corn leaf blight, grey leaf spot and head smut diseases, among others [14; 15]. Foliar diseases have been recorded as causing a high rate of severe damage in maize, with northern corn leaf blight disease alone capable of causing up to 50% production loss [16]. Furthermore, the development of secondary complications, which arise from severe foliar desiccation by the foliar pathogens, have been reported to result in severe lodging and up to 100% yield loss owing to stalk deterioration by grey leaf spot [16; 17]. However, the management of foliar diseases can be complicated since multiple pathogens are involved in disease occurrences. Hence, foliar diseases of maize constitute a major threat to the sustainable production of this important cereal. The management of the foliar diseases of maize with cultural methods such as tillage practices and crop rotations has only yielded limited effects [18; 19; 20]. Hence, reliance on fungicides, owing to their ease of application and efficacy, has been recorded previously over a range of pathogens [21; 22; 23]. However, their consequent harmful impact on the soil and human health necessitates the need to explore other promising alternatives, such as nanoparticles [24]. Nanoparticles are small particles that range between 1 to 100 nanometres in size, which are specially prepared from the active ingredients of the source materials to enhance their efficiency [25; 26]. They have been employed as nano-phytopathology for detecting, diagnosing and controlling plant diseases and their pathogens [27; 28; 29]. The action of the nanoparticles against fungal pathogens is by the inhibition of biofilm formation, destruction of cell walls, destruction of cell membranes or interaction with biomolecules [28; 30]. Hence, the application of nanoparticles was considered essential in this study since foliar diseases of maize at Molekwang, North-West Province of South Africa, have persisted over a range of management practices, from cultural to the use of chemical control. This study therefore set out to characterize the fungal pathogens associated with the foliar diseases of maize and evaluate their in vitro control using bismuth sulphide nanoparticles (Bi\({}_{2}\)S\({}_{3}\)) and graphitic carbon nitride nanoparticles (gC\({}_{3}\)N\({}_{4}\)). Bismuth sulphide is a metal-containing chalcogenide nanoparticle, while graphitic carbon nitride is a non-metallic, carbon-based nanoparticle.