By Blake Jackson
Physoderma brown spot is a noticeable foliar disease that occasionally appears in Kentucky corn fields, particularly during seasons with prolonged moisture.
According to Kiersten Wise, Extension plant pathologist; Brenda Kennedy, plant disease diagnostician; Kelsey Mehl, Extension associate; and Carl A. Bradley, Extension plant pathologist at the University of Kentucky, the disease is caused by the fungus Physoderma maydis and is favored by warm, wet growing conditions.
The disease is recognized by small purple to dark brown circular spots that commonly develop near the leaf midrib. As the infection progresses, these spots may merge into larger blotches, while tiny yellow or brown lesions can form across the leaf blades in distinct bands.
Similar symptoms may also appear on leaf sheaths, husks, and stalks, with signs often becoming visible before tasseling.
The fungus survives in corn residue and soil through specialized structures that remain dormant over winter. In spring, wind and splashing water spread these spores to young corn plants.
Infection occurs most readily when temperatures range from 75°F to 85°F, and moisture remains trapped in the plant whorl. Early vegetative-stage corn is most susceptible, while older plants develop greater resistance. Fields with continuous corn production or conservation tillage generally experience higher disease pressure.
Although Physoderma brown spot rarely causes significant yield loss, some corn hybrids are more vulnerable than others. Growers can reduce future disease risk by rotating crops and encouraging residue breakdown through tillage or other management practices.
Foliar fungicides labeled for Physoderma brown spot are available, but research on their effectiveness remains limited, making integrated cultural management the primary strategy for disease control.
Photo Credit: gettyimages-dale-fornoff
Categories: Kentucky, Crops, Corn, General