Corn Leaf Diseases and Fungicide Reminders

  • Jul 22
    Greg Stewart
    Corn Leaf Diseases and Fungicide Reminders By Greg Stewart on July 22, 2016
    Categories: Grain Corn, Silage Corn

    Northern Leaf Blight

    • Most widespread of the diseases
    • Elliptical shaped lesions usually begin on lower leaves
    • Recent research shows an increase in races of this disease which bypass resistant genes
    • Significant yield impact when infection is high or begins early


    Common Rust

    • Does not overwinter in Ontario
    • Early symptoms are yellow flecks on either side of leaf
    • Commercial hybrids have good tolerance
    • Moderate yield impact



    • Translucent yellow halo forms around infection – resembles an eye when held to sun
    • Sometimes confused with physiological fleck or insect damage
    • Economic losses due to eyespot are rare


    Gray Leaf Spot

    • Primarily exists in southwestern Ontario
    • Lesions are rectangular
    • Develops in lower leaves after tasselling
    • Most often associated with corn after corn and high residue
    • Moderate yield impact at current infection rates in Ontario



    • Fungicides are generally most efficient when applied at tassel stage and up to silk browning.  Applications that are earlier or later than these may not maximize the yield potential improvement.
    • Surfactants added to a fungicide application have been related to some pollination abnormalities, check with you supplier; products like Priaxor®, and Headline AMP® should not have surfactant added to the tank.
    • Only certain fungicides (i.e. Proline®, Caramba®) have shown to have any impact on reducing ear mould and vomitoxin levels, but timing is critical - silks must be emerged but not yet dried out.
    • Scouting and controlling Western Bean Cutworm may be significantly more important to reducing ear mould infection than a fungicide application.
    • If the timing works, an insecticide to control Western Bean Cutworm can be can be combined with a fungicide application.


    Greg Stewart
    Maizex Seeds Agronomy Lead

    Like what you’re reading? Sign up to receive weekly agronomy updates from Greg Stewart and the Maizex Agronomy Team right to your inbox! CLICK HERE