Gray Leaf Spot

Identify the DiseaseGray Leaf Spot (GLS) is a fungal disease caused by the pathogen, Cercosporaa zeae-maydis, which overwinters on corn residue. GLS is arguably one of the most important diseases in corn. According to the Crop Protection Network, in 2017, in 25 corn growing states and Ontario, Canada, GLS reduced yields by more than 187 million bushels — more than any other disease that season.

GLS infects corn when spores from infected residue are blown or splashed by rain onto the leaves. Lower leaves usually show infection first, and as the disease cycles, more spores are produced and the upper canopy will become infected too. After infection, it may take up to two weeks for lesions to appear. Since GLS lesions grow between veins, they appear somewhat rectangular in shape, since they are bordered on two sides by vascular tissue. As the disease grows, lesions elongate between those veins. Eventually, foliar lesions can grow together and completely kill leaves, reducing photosynthesis and resulting in premature death, leading to yield loss, low test weight and poor dry down. Corn suffering from foliar diseases like GLS are also more prone to stalk rot which can result in lodging.

Conditions favoring disease: Wet, warm weather (75°-85°F) and high humidity leading to long periods of leaf wetness, susceptible hybrids, infested corn residue on soil surface.

Impact: It is estimated that yield losses of 50% or more can occur with severe infections occur before dent stage.

Management: Headline AMP, Priaxor, Revytek and Veltyma are all labeled for prevention and control of Gray Leaf Spot. Fungicide applications at the VT (full tassel) or R1 (pollen shed) stage offer good control of GLS. However, if infection starts early or is severe, earlier applications may be necessary to prevent the disease from advancing to the ear leaf and above.

Always read and follow label directions.