Tar spot of corn

Tar spot complex is a destructive fungal disease affecting corn, caused primarily by the pathogen Coniothyrium phyllachorae. This disease is known for its distinctive dark spots, which can lead to significant physiological stress and yield reduction in maize crops worldwide.

The primary host for this fungus is corn. The disease manifests as small, raised, black lesions on the leaves and leaf sheaths, resembling splashes of tar. These lesions may be surrounded by a chlorotic halo that eventually turns necrotic as the leaf tissue dies back prematurely.

Favorable conditions for development include mild temperatures and high moisture levels, particularly persistent dew or heavy rainfall. The spores are primarily dispersed via wind and rain splash, allowing the fungus to progress rapidly throughout a field when environmental conditions remain conducive for infection.

The economic impact of tar spot is substantial, as it significantly reduces the plant's ability to photosynthesize. This leads to reduced grain filling, lower test weights, and increased stalk lodging, all of which pose major challenges for harvesting and negatively affect final grain yields.

Management strategies require a multi-faceted approach to reduce the inoculum load and protect the crop. Key tactics include:

• Selecting resistant corn hybrids.
• Managing crop residues to prevent overwintering of the fungus.
• Crop rotation to break the disease cycle.
• Applying timely foliar fungicides to suppress pathogen spread during the most susceptible growth stages.