The Disease Triangle

Understanding When Diseases Occur

Corn diseases, such as, Gray Leaf Spot and Northern Corn Leaf Blight, will began to appear late in the season. Diseases will occur when a pathogen comes in to contact with the right host crop under favorable environment conditions. The pathogen, host, and environment conditions make up the disease triangle; all three must be present for disease to occur.

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How the Disease Triangle Applies to Corn

Hybrid Sensitivity to Diseases

  • Some hybrids are more susceptible to certain diseases than others
  • Know your hybrid sensitivity to particular diseases
  • Even resistant hybrids can be infected under favorable conditions


  • Fungal diseases can survive the winter in crop residue from previous seasons
  • Not rotating crops can increase the chance of disease in corn on corn fields, especially if disease was present the previous season

Weather Patterns

  • The success of fungal disease greatly depends on the weather conditions
  • Cool, rainy, humid, overcast and/or foggy conditions typically favor increase the chance of disease
  • High winds, hail or other conditions that cause physical damage to the plant also increase chance of disease infection

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