By Blake Jackson
Purple leaf sheath, sometimes referred to as pollen rot or purple sheath blight, is a common corn disorder in Kentucky that can easily be mistaken for a plant disease.
According to University of Kentucky plant pathology experts Luke Warner, Kiersten Wise, and Will Barlow, the condition is noninfectious and does not harm the stalk or reduce plant health, despite its alarming appearance.
The disorder is identified by dark purple blotches or speckled discoloration on the leaf sheaths surrounding the corn stalk. Symptoms typically appear after pollination, around the blister (R2) growth stage, and are most noticeable on the ear leaf sheath and one or two leaves below it.
Unlike many corn diseases, the discoloration is limited to the sheath and does not spread to the leaf blades or the stalk beneath.
Purple leaf sheath develops under humid conditions, particularly after heavy rainfall or prolonged dew. Rather than being caused by a pathogen, the condition results from harmless saprophytic fungi and bacteria that grow on dead pollen and other organic material trapped between the leaf sheath and stalk.
Since these microorganisms feed only on dead tissue, they do not infect living plant tissue or damage the crop.
Farmers can confirm the disorder by peeling back the leaf sheath and inspecting the stalk underneath. If the stalk remains free of lesions or discoloration, the symptoms are likely due to purple leaf sheath rather than a disease.
The condition is often confused with Physoderma brown spot or anthracnose stalk rot. Physoderma brown spot produces tan to brown lesions on the sheath and stalk and may create yellow bands across leaves.
Anthracnose stalk rot causes black lesions and internal stalk decay. Unlike these diseases, purple leaf sheath affects only the outer sheath, making proper diagnosis important for avoiding unnecessary concern and management decisions.
Photo Credit: istock-darcymaulsby
Categories: Kentucky, Crops, Corn