Botrytis cinereais the causative agent of gray mold disease, and infects more than 1400 plant species, including important crop plants. In tomato,B. cinereacauses severe damage in greenhouses and post-harvest storage and transport. Plant viruses of theTobamovirusgenus cause significant damage to various crop species. In recent years, the tobamovirus tomato brown rugose fruit virus (ToBRFV) has significantly affected the global tomato industry. Most studies of plant-microbe interactions focus on the interaction between the plant host and a single pathogen, however, in agricultural or natural environments, plants are routinely exposed to multiple pathogens. Here, we examined how preceding tobamovirus infection affects the response of tomato to subsequent infection byB. cinerea. We found that infection with the tobamoviruses tomato mosaic virus (ToMV) or ToBRFV resulted in increased susceptibility toB. cinerea. Analysis of the immune response of tobamovirus-infected plants revealed hyper-accumulation of endogenous salicylic acid (SA), upregulation of SA-responsive transcripts, and activation of SA-mediated immunity. Deficiency in SA biosynthesis decreased tobamovirus-mediated susceptibility toB. cinerea, while exogenous application of SA enhancedB. cinereasymptoms. These results suggest that tobamovirus-mediated accumulation of SA increases the plants’ susceptibility toB. cinerea, and provide evidence for a new risk caused by tobamovirus infection in agriculture.