Maize yellow mosaic virus, provisionally referred to MaYMV, is a novel polerovirus reported in China, Brazil, Ecuador, and more recently in Africa. Despite the broad distribution of this potentially emerging virus, information is lacking on transmission, symptomatology, and possible interaction with other maize viruses. As MaYMV belongs to the genus Polerovirus, circulative transmission by aphids was hypothesized. In this study, we tested mechanical and aphid transmission of this virus using symptomatic maize samples collected in different locations of the state of São Paulo, Brazil. Along with leaves and whole plants, we also collected aphids in order to test for virus presence. Plant and aphid samples were submitted to total RNA extraction, reverse transcription, and then PCR with specific primers for MaYMV, sugarcane mosaic virus (SCMV), maize rayado fino virus (MRFV), and maize chlorotic mottle virus (MCMV). MaYMV was detected in maize samples from different regions of the São Paulo state, often in mixed infections with SCMV and/or MRFV, and in extracts of the corn leaf aphid, Rhopalosiphum maidis. MCMV was not detected in any of the samples. Sanger sequencing of a 947 bp MaYMV amplified fragment from a maize plant sample showed 96% identity in nucleotides to that of a fully sequenced isolate MaYMV-SP1 from Brazil. MaYMV was transmitted by R. maidis, but not mechanically. A MaYMV isolate obtained through aphid transmission caused mosaic symptoms, when in single infection of maize, and more severe symptoms characterized by interveinal necrosis, when in mixed infection with SCMV. These findings contribute to a better understanding of the transmission and epidemiology of MaYMV and other viruses found in coinfection, what is important for disease management.