Cropside: Corn leaf diseases

CONCERN OVER CORN leaf diseases, their identification, and their potential impact on yield has grown over the last two years. Here are the four most prevalent leaf diseases in Ontario.

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

EYESPOT
•    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 •