Maize Lethal Necrosis

Affected plants show chlorotic mottling that usually begins on the younger leaves and progresses to yellowing and necrosis of leaf margins and tissue. Severely infected plants become stunted, fail to produce or fill ears, and the growing point can die back in a symptom sometimes described as dead heart. Whole plants may die, and patches of dead or dying plants can appear across a field.

Maize lethal necrosis requires both Maize chlorotic mottle virus and a potyvirus to be present in the same plant. The potyvirus components are transmitted by aphids, while Maize chlorotic mottle virus can be spread by several chewing insects such as beetles and thrips, and can also be carried on seed and persist in soil and residue in some situations. When a maize plant acquires both viruses, the synergistic interaction produces the severe necrotic disease.

• Both viruses must infect the same plant to cause the severe disease
• Potyvirus components are spread mainly by aphids
• Maize chlorotic mottle virus is spread by several chewing insects and can be seed-borne
• Continuous maize and overlapping crops maintain virus and vectors year-round

Maize, including sweetcorn, is the primary host of concern; several grasses can host the component viruses and act as reservoirs. Continuous maize cultivation, overlapping planting dates, high vector activity, and movement of infected seed all favour the build-up and spread of the disease.

• Continuous or overlapping maize crops that maintain the viruses
• High populations of aphids and other insect vectors
• Movement or use of infected or untested seed
• Grass reservoirs that harbour the component viruses between crops

Because the disease depends on both viruses and their vectors, management targets the whole cycle: reducing virus sources, limiting vector spread, and breaking continuous maize cropping. Tolerant varieties and clean seed are central, supported by area-wide practices where the disease is established.

• Plant certified, tested seed to avoid introducing the viruses
• Grow tolerant varieties where they are available and recommended
• Use a maize-free break period and rotation to interrupt the virus cycle
• Manage insect vectors and control volunteer maize and grass reservoirs
• Synchronise planting across an area to avoid continuous host availability