This study provides evidence for frequent and multiple invasions of New Zealand's native grasses by exotic cereal and pasture viruses. Fifteen native and three exotic grasses from 29 North Island and six South Island sites were surveyed for the presence of viruses using enzyme-linked immunosorbent assay (ELISA). Barley yellow dwarf virus and Cereal yellow dwarf virus (BYDV, CYDV: Luteoviridae) and Cocksfoot mottle virus (CoMV, Sobemovirus) are widespread throughout New Zealand. CoMV, previously considered to have a natural host range restricted to Dactylis and Triticum, was detected in Poa anceps, P. cita, Festuca novae-zelandiae, and Chionochloa rubra. New virus host reports include BYDV-PAV in Microlaena stipoides and Dichelachne crinita; BYDV-MAV in P. cita, F. novae-zelandiae and Hierochloe redolens; and CYDV-RPV in P. cita and M. stipoides. Nominal logistic regression analyses showed a correlation between the presence of exotic grass species and virus incidence. Host range experiments for BYDV-PAV and CoMV were performed with selected native and exotic grasses, and the results are discussed in context of the field-survey findings.