Cause Maize dwarf mosaic virus (MDMV) was first found in Ohio in 1962 and was not known to be in the Pacific Northwest until 1977, when losses in sweet corn occurred in the Twin Falls area. Severe losses have occurred most years since 1962 in most major corn-producing states east of the Rocky Mountains and in California. MDMV is transmitted by aphids and can infect sorghum, Johnsongrass, yellow foxtail, crabgrass, and other wild grasses. There are several virus strains, which differ in their host range.
Symptoms Initial symptoms are small yellowish spots and streaks generally concentrated in the lower third of newly forming leaves in the plant's whorl. These may coalesce to form light green or yellow mosaic patterns. Mosaic symptoms may increase in extent and intensity over time but frequently decrease in intensity later in the season, making identification based on leaf symptoms difficult. If infection is early, plants may be stunted, only a third to half as tall as healthy plants. Infected plants may be barren or, if they form ears, seed fill may be spotty and incomplete.
Cultural control
- Field corn is more resistant than sweet corn. Sweet corn varieties vary in tolerance, and some are tolerant at some locations but not at others. More information is needed on the interaction between virus strain and variety before varietal recommendations can be made.
- Early-seeded sweet corn may escape aphid flights.
- Control weedy hosts.