Physoderma Stalk Rot of Corn
Stalk rot diseases occur in nearly all corn crops, leading to approximately 5% yield loss per year. Stalk rots can be more commonly found in high-yielding hybrids that produce large and heavy ears.
AgVenture Product and Technology Marketing Director Scott Hart recently noted the presence Physoderma stalk rot (PSR) in Iowa fields. PSR is caused by the same fungal pathogen that causes Physoderma brown spot (Physoderma maydis).
Early indicators of PSR include plants breaking at the first or second node. Nodes are black with some pith rot present. Infected nodes will snap easily when gently pushed.
Thousands of light brown sporangia (an enclosure where spore production and storage occur) will be visible with microscopic examination. Sporangia overwinter in soil and infected tissues. Moderate temperatures and standing rainwater in the whorl increase infection risk.
Scouting for stalk rots should begin before blacklayer and continue weekly until harvest. Test at least 100 stalks for intactness by pinching each stalk between the lower nodes or push each plant to see if it remains upright. If more than 15% have soft stalks or lodge easily, those fields should be scheduled for the earliest possible harvest.
Recommended action steps include crop rotation and tillage practices to reduce inoculum. Avoid placing susceptible hybrids in poorly drained areas. Work with your AgVenture Yield Specialist to ensure hybrids are appropriately placed in the future.
(Physoderma stalk rot symptoms: Nodes are black with some pith rot present. Image: A. Robertson)