Rhizoctonia ear rot

Rhizoctonia ear rot is a fungal disease caused by the pathogen Waitea circinata (formerly Rhizoctonia zeae). It is a soil-borne fungus that primarily targets the reproductive structures of plants. While it is often considered a minor disease compared to other ear rots, it can cause localized severe damage under specific environmental conditions.

The primary host for this pathogen is corn (maize). The disease can manifest as an ear infection, but the fungus is also capable of causing root rot and damping-off in seedlings. Due to its persistence in the soil and crop debris, it represents a long-term challenge for corn production in affected regions.

Symptoms of the disease are characterized by a dense, white to pinkish mycelial growth that develops between the husks and the ear. As the infection progresses, the fungus produces small, dark-brown or black sclerotia that look like tiny hard bodies embedded in the fungal mass. The infected kernels may become shriveled, discolored, and lose their structural integrity.

The development of Rhizoctonia ear rot is highly dependent on humidity and temperature. The disease is most prevalent in seasons characterized by high rainfall during the silking and grain-filling stages. High humidity within the husk leaf environment creates a microclimate that allows the fungus to proliferate rapidly, especially if the plants have been stressed by drought or prior mechanical damage.

Management strategies focus on reducing the primary inoculum source in the field. Cultural practices such as crop rotation, tillage to bury infected crop residues, and the use of well-adapted, healthy hybrids are critical for disease prevention. Chemical seed treatments are also effective in protecting the initial seedling stage from the soil-borne inoculum of this pathogen.