Like other viruses, corn viruses interfere with genetic signalling within the plant. Leaves that are distorted by the virus cannot function normally, so plants stop gaining size and die during stressful weather.
Maize White Line Mosaic Virus persists from year to years in damp soil, so always plant sweetcorn in well-drained soil, and avoid low, wet locations. Many sweetcorn varieties are resistant to common viruses; resistant varieties may show slight symptoms, and then outgrow the problem. Measures that reduce aphid and leafhopper populations will cut the risk of this and other viral diseases in the garden. Grow plenty of nectar-producing flowers to attract aphid predators including ladybirds, lacewings and hoverflies.
Infected plants will not make a good crop. Pull them up, cut them into pieces, and compost them in an active compost pile.