Rice necrosis mosaic virus was transmitted by sap inoculation and through soil to 2 weeds, Ludwigia perennis and Brachiaria ramosa. The virus was recovered from these weeds and transmitted to rice plants. The inner epidermal layer of the sheath of infected B. ramosa showed granular, oval, intracellular X-bodies, 5.2-7.8 .times. 5.9-10.4 .mu.m. Natural infection of these weeds in the field further supported their role as hosts of the virus.