Corn Rust

Puccinia sorghi, a fungus

Host Plants:

In the wild: Wood sorrel
On Crops: All types of sweetcorn and maize

Where Found:

Worldwide, wherever sweetcorn or maize is grown in temperate climates


Following a period of cool, wet weather with temperatures between 16-21C (60-70F), elongated cinnamon-coloured deposits develop on both sides of sweetcorn leaves. The brown dust particles in each streak are new rust spores.


Badly affected leaves turn brown early and drop off. Plants that lose leaves to rust are weakened and will not produce as well as healthy plants.

Preventing Problems:

Rust-causing fungi persist in soil in warm climates, and spread to other areas when spores are blown on winds. Some varieties offer genetic resistance. Leaves that dry rapidly after rain or heavy dew are unlikely to develop problems with rust. Avoid planting sweetcorn near trees, fences, or low pockets where dew is always heavy, and grow sweetcorn at proper spacing to make sure sunlight reaches all the leaves. The weed called wood sorrel serves as an alternate host for this disease, so eliminating this weed can limit corn rust. At the end of the season, compost all sweetcorn plants to speed the decomposition of diseased tissues.

Managing Outbreaks:

Stay out of your sweetcorn patch when the leaves are wet, because you can spread the spores from sick plants to well ones. On a dry day, gather badly affected leaves and dispose of them in the trash.

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