Infected johnsongrass rhizomes sprout and produce infected shoots in the spring or early summer. As the viruses multiply within newly developing tissues, symptoms eventually develop in a susceptible corn plant. Infected corn plants can then serve as a source of virus for new infections to both corn and seedling johnsongrass. MDMV is transmitted by several aphid species, most commonly the corn leaf aphid, the greenbug, and the green peach aphid. These aphids typically acquire MDMV very quickly during feeding activity, often as quickly as 15 to 60 seconds.
Viruliferous aphids are capable of infecting a plant after feeding for less than one minute.
Outbreaks of maize dwarf mosaic usually are most severe around areas of the field with infestations of infected rhizome johnsongrass. However, some studies have shown that viruliferous aphids may be blown some distance from infected johnsongrass, so the potential exists for outbreaks even in areas of a field with no johnsongrass. MDMV can be seedborne at very low levels, but infected seeds are not considered to be an important source of inoculum in Kentucky. MCDV is transmitted by several leafhopper species, most commonly the black-faced leafhopper. Outbreaks of maize chlorotic dwarf typically are limited to areas of the field with infestations of rhizome johnsongrass.