NPIPM:Stalk rots on corn
Authors: Byamukama, E. and Yabwalo, D.
Causal Organisms
Several pathogens cause corn stalk rots:
Anthracnose stalk rot - Colletotrichum graminicola
Diplodia stalk rot - Diplodia maydis (also known as Stenocarpella maydis)
Gibberella stalk rot - Gibberella zeae (asexual stage is Fusarium graminearum)
Physoderma stalk rot - Physoderma maydis
Fusarium stalk rot - Fusarium spp.
Symptoms and Signs
Stalk rot symptoms typically include wilting of plants leading to premature plant death. Infected plants may have discolored pith and roots maybe decayed depending on the type of stalk rot. Some stalk rot pathogens discolor the rind or develop fungal structures on the rind. The Anthracnose stalk rot fungus produces shiny black survival structures on the rind called acervuli which produce spores that infect young corn plants in spring. Diplodia stalk rot symptoms are characterized by dark brown/black small structures called pycnidia that are embedded in the rind of diseased stalks. The pycnidia can be easily dislodged from the surface of the stalk when rubbed off. Gibberella stalk rot typical symptom is pinkish-red discoloration of the inside of the stalk. Stalks with Gibberella stalk rot have small round black specks often near the node. Physoderma stalk rot is best noticed when leaf sheath is peeled off the lowest nodes. Infected stalks have dark brown to black spots by the node and when slightly pushed, the stalks snap at the node joint. Fusarium stalk rots do not develop distinctive symptoms and are usually diagnosed by the absence of the specific characteristics of other stalk rots above.
Disease Impacts
Stalk rots are quite common corn diseases. Yield losses range between 5-20% depending on the susceptibility of the hybrid. Stalk rots cause yield loss through reduced seed weight if the plants wilt before grain fill. Stalk rots also reduce yield when infected plant lodge to the ground and are not picked the combine during harvest. Lodged stalks may also lead to ear rots developing once the ears touch the soil or are exposed to high moisture on the soil surface.
Life Cycle and Epidemiology
Corn stalk rot pathogens overwinter in infected corn stalks or in the soil and release spores in spring. Spores are splashed onto leaves and stalks by rain. Infection is favored by warm and wet conditions. Stalk rot severity maybe exacerbated by stress on corn plants due to leaf diseases, low soil fertility, high planting population.
Management Approaches
• Select resistant hybrids
• Use a balanced soil fertility program
• Plant at an appropriate population
• Control foliar diseases
• Practice crop rotation to manage corn residue
Other Online Resources
Freije, A. Nielsen B. and Wise, K. Stalk rots. https://www.extension.purdue.edu/extmedia/BP/BP-89-W.pdf
Crop Protection Network. Fusarium stalk rot of corn. https://cropprotectionnetwork.org/encyclopedia/corn-disease-management/stalk-and-root-diseases/fusarium-stalk-rot/
