NPIPM:Gray leaf spot on corn
Authors: Byamukama, E. and Yabwalo, D.
Causal Organism
Gray leaf spot of corn is caused by a fungal pathogen Cercospora zeae-maydis (Syn. Mycosphaerella spp).
Symptoms and Signs
Gray leaf spot starts as small necrotic (dead tissue) light-tan spots. These expand in length to become rectangular and can reach 2 inches but they are limited within leaf veins (regular). With time and depending on the hybrid and environmental conditions, the lesions turn gray. The lesions may have a dark border or a yellow halo. The diagnostic symptom of gray leaf spot is the sharp parallel edges of the lesion. Symptoms usually start from lower leaves and progress to mid and upper canopy, depending on the weather conditions.
Disease Impacts
The extent of yield loss depends on the severity of the disease (number of lesions and leaves affected relative to the ear leaf). Heavy lesions on the ear leaf or higher about two weeks prior and/or after tasseling can result in yield loss.
Life Cycle and Epidemiology
The gray leaf spot pathogen survives on corn residue and in the soil. In spring, spores called conidia are disseminated by wind or rain splash onto corn leaves. Under high relative humidity (>90%) and warm conditions, the spores germinate on the leaves and initial symptoms start to develop between 2-3 weeks. Symptoms severity depends on weather conditions and the susceptibility of the hybrid planted.
Management Approaches
• Select resistant hybrids especially for corn on corn and in no-till fields
• Rotate crops to break the disease cycle.
• Manage corn residue through tillage where practical
• Apply a foliar fungicide if disease pressure and environmental conditions warrant the fungicide.
Other Online Resources
Wise, K. Gray leaf spot of corn. https://www.extension.purdue.edu/extmedia/BP/BP-56-W.pdf
Crop Protection Network. Gray leaf spot of corn. https://cropprotectionnetwork.org/encyclopedia/corn-disease-management/foliar-diseases/gray-leaf-spot/
