Northern Leaf Blight of Maize

The disease begins as small, elliptical, water-soaked lesions that expand into long, grey-green to tan, cigar-shaped blights running along the leaf. Lesions typically start on the lower leaves and move upward. Under humid conditions, a dark, dusty layer of spores may form on older lesions. When lesions coalesce, entire leaves can be blighted and appear scorched.

Exserohilum turcicum survives between crops on infected maize residue. Under moderate temperatures and humid conditions it produces spores (conidia) that are dispersed by wind and rain splash onto the lower leaves of a new crop. Repeating infection cycles then move the disease up the canopy, with long periods of leaf wetness strongly favouring each cycle.

• Infected maize residue carries the fungus between seasons
• Wind- and rain-dispersed conidia infect the lower leaves first
• Moderate temperatures with high humidity and leaf wetness favour infection
• Repeating cycles move the disease up toward the ear leaf during grain fill

Maize, including sweetcorn, is the main host, and sorghum can also be affected by forms of the fungus. The disease is favoured by moderate rather than hot temperatures combined with high humidity and frequent dew or rain. Continuous maize with surface residue and susceptible hybrids increases the risk of early, damaging epidemics.

• Moderate temperatures with prolonged high humidity and leaf wetness
• Continuous maize with infected residue retained at the surface
• Susceptible hybrids that allow large lesions to develop
• Cool, humid highland and temperate environments during grain fill

Resistant hybrids are the primary tool, including those with major resistance genes and those with broader partial resistance, supported by cultural measures that lower residue-borne inoculum. Integrating these tactics gives more durable protection than any single measure.

• Choose hybrids with strong northern-leaf-blight resistance ratings
• Rotate away from maize and manage residue to reduce inoculum
• Scout the mid and upper canopy from tasselling through grain fill
• Favour practices that reduce prolonged leaf wetness where feasible
• Prioritise fields with a history of the disease or dense canopies