HPIPM:Helminthosporium Leaf Blight FC

Author: Howard F. Schwartz, David H. Gent, and William M. Brown, Jr.

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Dothideomycetes
Subclass	Pleosporomycetidae
Order	Pleosporales
Family	Pleosporaceae
Genus	Exserohilum

Scientific Name

Exserohilum turcicum

Scientific Name Synonyms

Bipolaris turcica

Helminthosporium inconspicuum

Helminthosporium turcicum

Setosphaeria turcica

Common Name

northern corn leaf blight

Identification and Life Cycle

Helminthosporium leaf blight is a general term for several diseases caused by several fungi formerly known as Helminthosporium spp. These diseases include Southern corn leaf blight (caused by Cochliobolus heterostrophus), Northern corn leaf blight (caused by Setosphaeria turcica), and Northern corn leaf spot (caused by Cochliobolus carbonum). Infection of susceptible varieties occurs when temperatures are moderate (64 to 80ºF) to warm (68 to 90ºF) and damp, humidity, weather prevails. Helminthosporium leaf blight pathogens survive between corn crops as spores (conidia) and mycelium in and on crop debris, but can also be transported long distances on wind currents.

Plant Response and Damage

Disease symptoms of Helminthosporium leaf blights can vary among inbreds and hybrids. Southern corn leaf blight symptoms include tan, elongated lesions between veins with light brown to brown borders. Northern corn leaf blight causes gray-green, elliptical or cigar-shaped lesion approximately 0.4 to 6 inches long. As lesions age they become tan with distinct dark zones. Northern corn leaf spot lesions are varied, but typically include oblong dark brown spots on leaves of maturing plants. Symptoms may also include narrow, grayish tan with light to dark border lesions on leaf blades, sheaths, and husks. Black felty mold on kernels can also occur with some strains of the Northern corn leaf spot fungus. Yield losses from these diseases are generally minimal in the High Plains region, but can be significant on susceptible inbred lines during weather conditions favorable for disease, especially when infection occurs before silking.

Biological Control

Practical biological control strategies have not been developed for Helminthosporium leaf blights.

Cultural Control

Conventional tillage and sanitation of crop residues in the fall along with crop rotation can reduce primary inoculum, and generally are sufficient in the High Plains region, but may not be adequate under disease favorable conditions. Resistant varieties are available and should be planted. Several races of the Helminthsporium leaf blight pathogens exist, so single-gene resistance may not be effective against all strains of each pathogen. Varieties with general resistance are available that do not completely control disease, but reduce the number and size of lesions.

Chemical Control

Fungicides applied when lesions first appear effectively control Northern corn leaf blight, but may only be cost effective on high-value seed-production fields or sweet corn. Fungicides may be most effective when combined with varieties with general resistance.

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.