The wet growing conditions in June provided the ideal environment for the development of Physoderma brown spot in corn. Infection requires a combination of light, free water, and warm temperatures (75-8 *F). Leaf infection occurs in the whorl when water is present for an extended time.
Hybrids vary in their susceptibility to the disease and severe outbreaks of Physoderma have been associated with stalk rot and breakage. It can survive in the soil and crop residue for up to 7 years. Crop rotation and tillage reduce survival of inoculum.
- Usually appear on mid-canopy leaves and on the stalk, leaf sheath, and husks
- Appears in broad bands across the leaves
- Lesions are approximately ¼ inch in diameter
- Round to oval, yellowish to dark brown in color
- Alternating bands of infected and non-infected tissues are commo
- Dark purplish to black oval spots also occur on the midrib of the leaf
- Blackening of lower stalk nodes and potentially some stalk rot of the pith
Foliar fungicides labeled for Physoderma brown spot are available.