Necrotrophic pathogens, such as Sclerotinia sclerotiorum and Botrytis cinerea, threaten global agricultural production. Traditional agrochemicals may negatively impact the environment and chemical resistance is rising. Therefore, novel strategies are needed to overcome these obstacles. RNA interference (RNAi), a cellular defence pathway for targeted mRNA degradation using double stranded RNA (dsRNA), could be a next-generation fungicide. RNA sequencing of the host-pathogen interface identified hundreds of genes for RNAi-based control development. I first demonstrated the dsRNA molecules elicited gene silencing in vitro. Next, I formulated foliar applications to protect both Brassica napus and Arabidopsis thaliana from S. sclerotiorum and B. cinerea using designer molecules targeting homologous transcripts. Finally, I engineered host induced gene silencing (HIGS) to suppress fungal colonization on A. thaliana and explored host defense and death responses during HIGS. Together, these findings provide compelling evidence for an RNAi-based biotechnological management strategy and will be a valuable resource for future research endeavours.