Northern Corn Leaf Blight

Northern corn leaf blight is caused by the fungus Exserohilum turcicum, teleomorph Setosphaeria turcica. Both the common name and causal organism have several synonyms. Host of E. turcicum include corn, sorghum, Sudangrass, Johnsongrass, gamagrass and teosinte. Exserohilum turcicum is divided into 3 races and infection of hosts from different genera and species is dependent on the race. In addition, two biotypes have been identified from maize. The fungus overwinters as mycelium, conidia and chlamydospores in and on plant debris. Spores are windblown or splashed by rain from plant debris to the current season crop. Conidiospores of Exserohilum turcicum have a slightly protruding hilum which aids in identification of the fungus. The conidiospores germinate and penetrate leaf tissue directly or through stomata. Infection occurs when free moisture is present on the leaf surface.

Symptoms

Symptoms develop on lower leaves first and progress up the plant under favorable weather conditions ( temperatures of 60-90^o and high relative humidity). Several types of lesions may occur on leaves and husks. The type of lesion present is dependent on host resistance genes. The typical symptoms seen on a susceptible host are long elliptical spots up to 15 cm in length.. Spots are grayish-green to tan in color. Spore produced in the lesions are olive-green to black and may be produced in concentric rings giving the spot a target like appearance. Spores from the primary lesions reinfect the host producing secondary cycles of the disease. Lesions produced on hybrids with polygenic (quantitative) resistance are long and narrow resembling those of Stewart's wilt. These lesions may extend the entire length of the leaf. Fewer lesions are produced on these hybrids and their size, in term of surface area affected, is less than on susceptible hybrids. Lesions produced on hybrids with monogenic resistance are characterized as small necrotic spots that are surrounded by a chlorotic halo. Spore is greatly reduced or absent in these lesions.

Plant Health Management

Resistant Hybrids

Hybrids are available with both monogenic and polygenic resistance and should be used whenever possible.


Residue Management

Severe outbreaks of northern corn leaf blight are sporadic but the potential for a major outbreak is present where corn is being continuously cropped in a conservation tillage system. Since the fungus that causes the disease survives between seasons on crop residue, reduction of the residue should reduce the amount of inoculum present in the spring. However, it is not practical (or legal in some government programs) to abandon conservation tillage. In this case a grower may find it useful to rotate to an unrelated crop such as soybeans.




Fungicide Application

Several fungicides are labeled for control of northern corn leaf blight. Mancozeb and propiconazole are labeled for field corn, popcorn and sweet corn.

Maneb and maneb plus zinc are also labeled for control on popcorn and sweet corn. (1997) Fungicide application may be cost prohibitive in some situations and may be limited to seed production fields. Applications may also be prohibited past a certain growth stage and restrictions may apply to feeding crop residue to livestock.

References

Agrios,G.N.1988. Plant Pathology (3rd ed.) Academic Press, Inc., San Diego. pp 359- 356.


Nyvall, R.F.1989. Field Crop Diseases Handbook (2nd ed.). Van Nostrand Reinhold, New York. pp.124-25.

Schurtleff, M.C. (ed.). 1980. Compendium of Corn Diseases (2nd ed.). American Phytopathological Society, St. Paul, MN, pp.17-18.

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This page was drafted by: Jane Christensen, Department of Plant Pathology, University of Nebraska-Lincoln

Disease images were provided by: Dr. David Wysong, Department of Plant Pathology, University of Nebraska-Lincoln

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This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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