Physoderma stalk rot of corn
Physoderma stalk rot is caused by the same fungal pathogen that causes Physoderma brown spot, Physoderma maydis. It is not usually an economic problem. Stalk rot symptoms are first noticed when plants break at the first or second node. These nodes are black and some pith rot may be present. Infected nodes snap easily if gently pushed. Microscopic examination of symptomatic tissue reveals thousands of light brown sporangia (an enclosure where spore production and storage occurs). Sporangia overwinter in soil and infected tissues. Moderate temperatures (73–86°F) and standing rainwater in the whorl increase infection risk. Infection of nodes 6 and 7 may result in stalk rot. Young plants become more resistant with age. Choose resistant hybrids and avoid susceptible hybrids in poorly drained areas to reduce infection risk. Crop rotation and tillage practices may reduce inoculum.
Gallery Images: A. Robertson and D. Mueller