Northern corn leaf blight

Northern corn leaf blight (Setosphaeria turcica) is a serious fungal disease prevalent in cooler climates and tropical highlands wherever corn is grown. It is a major constraint to maize production in many maize growing regions worldwide with a growing season characterized by high humidity and moderate temperatures (17 to 27°C). It is characterized by large cigar shaped necrotic lesions that develop on the leaves.

Symptoms
Symptoms of S. turcica are easily recognized. Early symptoms are oval, water-soaked spots on leaves. Mature symptoms are characteristic cigar shaped lesions that are 3-15cm (1-6in) long. Lesions are elliptical and tan in color, developing distinct dark areas as they mature that are associated with fungal sporulation. Lesions typically first appear on lower leaves, spreading to upper leaves and the ear sheaths as the crop matures. Under severe infection, lesions may coalesce, blighting the entire leaf.

Lesions may vary slightly depending on the resistance status of the host. Lesion development on some hybrids with resistance genes may include long, chlorotic streaks that can be confused with other diseases such as Stewart's wilt.

Host resistance

 * Host resistance is the most efficient and cost effective means of disease resistance.
 * Four genes offering major resistance to S. turcica have been identified and are incorporated in many commercial hybrids. However, success of disease management using qualitative resistance will depend on the race of the pathogen present.
 * Quantitative levels of host resistance are also available that restrict lesion development and sporulation.

Cultural control

 * Rotating maize with non-host crops can reduce disease pressure.
 * Management of overwintering infected crop residue will reduce the amount of available inoculum at the onset of the subsequent growing season.

Fungicides

 * Fungicide application can effectively control S. turcica when applied at the right time. Fungicide should be applied when lesions first become visible on the lower leaves.
 * In seasons not favorable to S. turcica (cool and dry seasons), fungicide application may not be cost effective particularly for grain production.