Northern leaf blight

What is northern leaf blight ? 

Northern leaf blight (Exserohilum turcicum) is a yield-limiting disease that affects maize crops. It is most prevalent during moderate temperatures (17°C to 27°C) combined with prolonged periods of moisture, and typically appears at or after silking. Yield losses are most severe when northern leaf blight infects maize plants early and reaches the upper leaves by the beginning of ear fill. 

When infected, northern leaf blight forms elliptical, grey-to-tan lesions on leaves that range from 1 to 6 inches long. Infection often starts on the lower leaves, where humidity is highest. Northern leaf blight spores coat the area, giving it a dark, dirty appearance. This may cause plants to lose their lowest leaves, weakening the crop and reducing yields. Effective northern leaf blight management strategies are essential to combat the disease.

What is the lifecycle of northern leaf blight?

The lifecycle of northern leaf blight is weather-dependent, as certain conditions encourage the spread of the fungal pathogen between maize plants. The cycle follows these key steps:

1. Fungus overwinters – The fungus survives in infected plant debris, such as leaves and husks, as mycelia and conidia (spores).
2. Spore dispersal – In spring and early summer, conidia are spread to new leaves by wind and rain.
3. Infection and symptom development – Once on the leaves, the fungus infects the plant under favourable conditions, leading to symptom development, including lesions.
4. Secondary spread – Spores from leaf lesions are further dispersed by wind and rain, continuing the infection cycle.
5. Infected plant – The disease spreads, affecting more of the plant and potentially reducing yield.

This cycle repeats each season. Heavy dews, frequent light showers, high humidity, and moderate temperatures increase the spread and development of northern leaf blight. Lesions on the ear leaf and significant loss of green leaf area can result in yield loss, emphasising the role of environmental conditions in disease progression and the need for effective control. 

Why is northern leaf blight a problem?

Yield loss from northern leaf blight can be significant—ranging from 30% to 50%. If lesions appear on the ear leaf two weeks before or after tasseling, and conditions are favourable for disease development, this is when the greatest yield losses occur.

In severe cases, lesions can merge across large areas of leaf tissue, causing excessive blighting. This reduces the photosynthetic capacity of the plant, forcing it to draw on stalk reserves to complete grain fill. As a result, plants become prone to stalk rot and standability issues.

How do I control northern leaf blight?

The most effective strategy to reduce yield loss is to use a combination of management methods:

1.  Choose hybrids resistant to northern leaf blight

Hybrids with partial resistance typically produce fewer and smaller lesions, as well as fewer fungal spores—reducing 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 

Varietal resistance, although limited, can contribute to lowering infection levels.

Pioneer Research Hybrid Northern Leaf Blight Resistance Scores 2024
(9 = Resistant, 1 = Susceptible)

2. Reduce previous maize residue

Reduce maize residue by rotating crops or utilising tillage methods that place soil in contact with residue. This promotes decomposition and decreases the amount of disease material surviving into the next cropping season. However, reducing residue does not protect against spore showers carried into the field by wind currents.

3. Plant at the right time

Timely planting helps maize grow faster than the disease can spread, reducing the risk of severe damage. Late-planted maize is more vulnerable because it gets infected earlier when plants are smaller.

However, in severe outbreaks, both early- and late-planted maize can still be heavily affected.

4. Consider a fungicide application

Approved foliar fungicides are available to help control or suppress northern leaf blight development.