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Corn+Soybean Digest

Corn Diseases


  • TWO FORMS: leaf blight and stalk rot.
  • SYMPTOMS: Leaf blight: lesions varying in size, generally brown and round-shaped with yellowish area surrounding. First appear on leaf tip, moving to midrib, then produce large, dead spots. Stalk rot: Shiny, black streaks and blotches on the lower stalk. Internal stalk tissue can turn dark gray to brown and become shredded.
  • TIME OF ATTACK: Anytime from seedling emergence to maturity. Leaf symptoms can begin in May; stalk rot symptoms usually appear in late August to mid-September.
  • CONDITIONS FAVORING: Cool, wet weather.
  • MANAGEMENT: Tillage, crop rotation, resistant hybrids. Scout and apply fungicide if necessary for foliar stage of disease.


  • SYMPTOMS: A sudden onset of grayish-green color of the leaves; lower part of the stalk turns from dark green to light tan; the pith inside the stalk becomes soft. When diseased stalks are split, the pith usually has a reddish or pinkish discoloration and shows signs of deterioration. Pink to reddish mold that begins at the tip of the ear and develops toward the base.
  • TIME OF ATTACK: After silking in cool, wet weather.
  • CONDITIONS FAVORING: Cool, wet weather after silking; continuous corn; stress due to extreme weather conditions, unbalanced soil fertility and high plant populations.
  • MANAGEMENT: Tillage, rotation, resistant hybrids.


  • SYMPTOMS: seedling blight causing death of young plants; long, slender lesions with wavy margins extending between veins; dark green to black irregular spots.
  • TIME OF ATTACK: Any stage with leaves.
  • CONDITIONS FAVORING: Injury to corn leaves; hail damage; continuous corn.
  • MANAGEMENT: Rotation, conservation tillage, resistant hybrids.


  • SYMPTOMS: Small, linear, rectangular-shaped lesions, tan to gray in color. Lesions begin on lower leaves and spread upward.
  • TIME OF ATTACK: Lesions generally appear near first tassel; disease spread continues through maturity.
  • CONDITIONS FAVORING: Cloudy days with humid or wet conditions; heavy dew, fog or light rain. Continuous corn and reduced tillage also favor this disease.
  • MANAGEMENT: Resistant hybrids, tillage, crop rotation, scouting and fungicide application if necessary


  • SYMPTOMS: Elliptical brown to grayish to tan lesions from 1 to 6 in. long. If humid, lesions may have gray-green centers due to spores on dead tissue.
  • TIME OF ATTACK: As early as silking, but more prevalent during later development stages.
  • CONDITIONS FAVORING: Wet, humid weather; heavy dew and fog. Can also have higher rate in continuous corn and reduced tillage.
  • MANAGEMENT: Resistant hybrids, tillage, crop rotation.


  • SYMPTOMS: Light cinnamon brown to orange uredia densely scattered on upper leaf surface (more orange than common rust). Black telia form in circles around uredia when leaves start to die.
  • TIME OF ATTACK: When warm, humid conditions are present.
  • CONDITIONS FAVORING: Warm, humid weather.
  • MANAGEMENT: Foliar fungicides at proper timing if cost will be economic.
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