Common rust is a fungal disease affecting maize, wheat and barley crops, causing yield loss, especially under favourable environmental conditions.
Common rust
What is common rust?
Common rust is a fungal disease caused by the Puccinia sorghi pathogen. It affects maize, wheat and barley crops, causing yield loss, particularly in moist, cool climates (16–25 °C). The disease slows or halts in hot, dry conditions.
Due to climate change, milder winters and warmer springs are causing earlier and more widespread outbreaks across the UK.
When infected, common rust forms orange-to-brown colour pustules (about 0.5–1.0 mm in diameter). The pustules darken over time and contain rust spores.
What causes common rust in maize, wheat and barley crops?
Common rust is caused by Puccinia sorghi, which lands on leaves and infects crops. As the fungal disease develops, it forms pustules that darken and produce rust spores.
The fungus can only grow and survive on live leaf tissue. Symptoms appear on crops within 3-4 days of infection, starting as chlorotic (yellowish) flecks or spots on both leaf surfaces.
After infection, common rust typically produces pustules and spores within 7 to 14 days, leading to rapid secondary infections. If conditions are favourable, wind can spread the disease quickly, resulting in potential epidemics.
The fungus overwinters as spores, which are carried and dispersed by wind. Yield losses typically range from 3–8%, but can reach up to 10% in severe disease cases.
How to identify common rust in crops?
Early signs of common rust include yellowish flecks on lower leaves. Within a few days, these develop into rust-coloured pustules that darken as the disease develops, then fill with cinnamon-coloured spores. As the disease matures, it spreads across the rest of the leaves but does not affect sheaths, stalks, ear shanks, or husk leaves.
Mature lesions range from 0.5–1.0 mm in diameter and, in severe cases, cover both sides of the leaf, causing extensive chlorotic spotting. This weakens the crop and reduces yields.
What is the lifecycle of common rust?
The life cycle of common rust can involve up to five spore stages, which vary depending on certain weather conditions. For example, white rust pustules may change from buff to white when in high humidity.
The fungus survives winter as spores in humid conditions. These spores are carried long distances by wind and have been found in the north of the UK.
Rust development is favoured by high humidity, with night temperatures of 65-70°F, and moderate daytime temperatures. The disease is usually more severe on seed corn.
The life cycle of common rust is somewhat weather-dependent as humid and windy certain conditions encourage the spread of the fungal pathogen.
The lifecycle follows these key steps:
- Fungus overwinters – The fungus survives the winter as spores in high-humidity conditions.
- Spore dispersal – In spring and early summer, the spores spread across large distances.
- Infection and pustule development – Spores land on leaves and infect plants. Reddish pustules form on leaves and turn black when mature, releasing cinnamon-coloured spores.
- Secondary spread – Spores disperse from plant to plant and field to field via wind, continuing the infection cycle.
- Infected plant – The disease spreads further, affecting more of the plant and potentially reducing yield.
Why is common rust a problem?
Common rust is a problem for plants in the UK because it thrives in mild, moist conditions, leading to increased infections, leaf discolouration, reduced growth, and potential plant death if left untreated.
Yield loss from common rust can be slight, only affecting crops up to 10% when the disease is severe however, rust spores are easily spread by wind causing rapid outbreaks.
How do you control common rust?
Effective control requires a multi-faceted approach, as crop rotation and tillage are ineffective (the disease does not overwinter in crop residue).
1. Choose hybrids resistant to common rust
Hybrids with partial resistance to common rust typically produce fewer and smaller pustules as well as fewer fungal spores, which can reduce the spread and impact of the disease on yield.
We offer a range of extra early, very early, intermediate and late-maturing maize hybrid varieties. Find out more about our maize hybrids >
2. Cultural control
Remove old plant debris that may host rust, and inspect new plants for symptoms of common rust before cultivating. If using a greenhouse, minimise humidity by increasing ventilation, spacing, and using fans, and monitor environmental conditions to avoid condensation.
3. Consider a fungicide application
Fungicides will provide effective control against common rust when applied at the appropriate time in combination with cultural control measures.
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