Trade or sharing that moves infectious planting material between farms can, for vertically transmitted plant diseases, act as a significant force for the dispersal of pathogens, particularly where the extent of material movement may be greater than that of infected vectors or inoculums. The network over which trade occurs will then affect dispersal and is important to consider when attempting to control a disease. We consider the difference that planting material exchange can make to the successful control of cassava brown streak disease, an important viral disease affecting one of Africa’s staple crops. We use a mathematical model of smallholders’ fields to determine the effect of informal trade on both the spread of the pathogen and its control using clean-seed systems, determining aspects that could limit the damage caused by the disease. In particular, we identify the potentially detrimental effects of markets, and the benefits of a community-based approach to disease control.