Amaranth anthracnose

The disease is caused by the fungus Colletotrichum hanaui, a member of the Ascomycota division. This pathogen is a significant threat to amaranth production worldwide. The fungus survives as mycelium or conidia on infected crop debris and in the soil, serving as a primary source of inoculum for subsequent growing seasons.

The host range of Colletotrichum hanaui is primarily limited to species within the Amaranthaceae family. The pathogen attacks seedlings, stems, and leaves, significantly impacting the crop's vegetative development. In severe cases, the infection results in seedling damping-off, leading to significant stand reduction and potential total crop failure if left unmanaged.

Diagnostic symptoms include the formation of irregular, water-soaked, dark-brown spots on the foliage. As the disease progresses, these lesions enlarge and often develop a lighter center with a distinct dark border. The presence of numerous small, black acervuli within these lesions is a diagnostic feature used to identify the presence of the pathogen in the field.

Environmental conditions play a critical role in the epidemiology of amaranth anthracnose. The fungus thrives in environments with high relative humidity and temperatures ranging from 20 to 30 degrees Celsius. Extended periods of rainfall or overhead irrigation facilitate the dispersal of spores from the soil surface to the lower canopy, initiating the infection cycle.

Effective management strategies should focus on integrated pest management practices:

• Crop rotation with non-host species to break the disease life cycle.
• Removal and destruction of infected plant debris post-harvest to reduce inoculum levels.
• Use of certified, high-quality, and fungicide-treated seeds.
• Management of soil fertility to ensure strong, vigorous plant growth that is more resistant to invasion.
• Timely application of chemical or biological fungicides when weather conditions are favorable for pathogen development.