Northern corn leaf blight

With its characteristic cigar-shaped lesions, this disease can cause significant yield loss in susceptible corn hybrids.

The most economically important host is corn, but other forms may infect sorghum, Johnson grass, or sudangrass.

[2] The most common diagnostic symptom of the disease on corn is cigar-shaped or elliptical necrotic gray-green lesions on the leaves that range from one to seven inches long.

Fully developed lesions typically have a sooty appearance during humid weather, as a result of spore (conidia) formation.

As the disease progresses, the lesions grow together and create large areas of dead leaf tissue.

The lesions found in Northern corn leaf blight are more acute if the leaves above the ear are infected during or soon after flowering of the plant.

In temperate regions, the fungus overwinters mycelia, conidia, and chlamydospores in the infected corn debris.

[2] When conditions become favorable the following season, conidia are produced from the debris and dispersed by rain or wind to infect new, healthy corn plants.

[2] In conditions with high humidity, the fungus will produce new spores at the leaf surface, which are spread by rain or wind through the crop and create cycles of secondary infection.

[8] On a global scale, NCLB is a problem in corn-growing areas in the mid-altitude tropics, which have the wet, cool environment that is favorable for disease development.

[5] A combination of crop rotation for one to two years followed by tillage is recommended to prevent NCLB disease development.

[5] Research suggests that using fungicides to keep the upper 75% of the leaf canopy disease-free for three quarters of the grain-filling period will eliminate yield loss [11] To ensure that newly emerging leaf tissue is protected from infection, before the plants are in tassel, fungicides should be applied on the same day that significant conidial dispersal is expected to occur.

[12] The disease pressure in the field and weather conditions should be monitored and evaluated beforehand to determine if fungicides are needed or not.

If severe disease is present two to three weeks after silking in field corn, grain yields may be reduced by 40 to 70 percent.

[7] Researchers in Hokkaido, Japan have also discovered that NCLB reduces the quality of corn silage as animal feed.

[5] Following conidia germination, the fungus forms an appressorium, which penetrates the corn leaf cell directly using an infection hypha.