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A Smorgasbord of Corn Foliar Diseases

Dean Malvick Dean Malvick
Assistant Professor
Department of Crop Sciences
(217) 265-5166; dmalvick@illinois.edu
Don White
  Don White
Professor
Department of Crop Sciences
(217) 333-1093; d-white@illinois.edu
Jerald K. Pataky  


Jerald K. Pataky
Professor
Department of Crop Sciences
(217) 333-6606; j-pataky@illinois.edu

Many cornfields in every county in Illinois experience foliar disease each year. As history has shown repeatedly, corn diseases periodically can and do cause significant yield losses in patterns that often are difficult to predict in advance. Corn diseases typically cause minimal damage over the entire state; however, some acreage suffers disease damage each year.

Many different foliar diseases affect corn in Illinois. The occurrence of any specific disease depends on environmental conditions and the hybrid grown. The basis of good disease management practices is proper identification of the disease. In the plots at our field stop, various lines of corn are infected with the following diseases, so you’ll be able to examine corn diseases and practice disease identification skills.

A B C

Figure 1. Which of these is a viral, bacterial, and fungal disease,
and what are the names of these diseases? (See answers in text on this page.)

Anthracnose Leaf Blight. Symptoms: Lesions are initially water-soaked and enlarge to develop tan centers and reddish-brown borders. The lesions may merge to form large dead areas. Tiny black spines may be seen in the lesions with a hand lens.

Aspergillus Ear Rot. Symptoms: Infection usually is limited to a few kernels on an ear. Masses of yellow-green or yellow-brown spores often are seen on or between infected kernels.

Common Corn Smut. Symptoms: Galls on leaves, ears, stalks, or tassels covered with a glistening, greenish white to silvery tissue. Galls become filled with masses of powdery dark spores.

Common Rust. Symptoms: Small, irregular yellow spots develop between the leaf veins. Cinnamon-brown, powdery pustules are common on both leaf surfaces.

Diplodia Ear Rot. Symptoms: Husks may appear bleached or straw-colored, and the entire ear may turn grayish-brown. White mycelium grows between the kernels of infected ears, starting from the base.

Eyespot. Symptoms: Upper leaves have 1/10- to 6/10-inch, oval to round, tan-colored spots surrounded by a dark brown/purple ring and a narrow, transparent yellow halo.

Gray Leaf Spot. Symptoms: Lesions are rectangular and elongated (photo 2), bordered by veins, tannish to bleached brown.

Maize Dwarf Mosaic Virus. Symptoms: Leaves often are mottled with small, light and dark green patches, which may develop into narrow, yellowish streaks along the veins (photo 3). Stunting may occur.

Northern Corn Leaf Blight. Symptoms: Long, elliptical, grayish-green or tan lesions (often cigar-shaped) appear on lower leaves first.

Northern Corn Leaf Spot. Symptoms: Lesions are tan, oval to circular, and usually measure ½ to 1 inch.

Southern Corn Leaf Blight. Symptoms: Small, elongated (¼- to ½-inch) tan lesions with parallel sides and buff to brown borders.

Southern Rust. Symptoms: Small, irregular yellow spots develop between the leaf veins. Light cinnamon-brown to orange pustules usually appear after silking on the upper leaf surfaces, stalks, and husks.

Stewart’s Wilt. Symptoms: Long, irregular, pale green streaks with wavy margins that become yellow and straw-colored (photo 1). Sweet corn and some inbreds are most susceptible. Seedlings may be stunted and wilted.

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