Onion rust

Uromyces probus is a fungal pathogen responsible for causing rust disease in various Allium species, particularly cultivated onions. As a member of the rust fungi group, it acts as an obligate parasite, deriving all its nutritional requirements from the living tissues of the host plant.

This disease primarily impacts Allium crops, including common onions, shallots, and garlic. The infection manifests in the vegetative parts of the plant, significantly hindering growth and reducing the market quality of the bulbs due to the reduction in foliage vitality.

The primary symptom involves the development of small, chlorotic spots on the leaves, which eventually evolve into raised pustules. These pustules rupture the leaf epidermis to release urediniospores, which can be spread rapidly by wind currents, splash irrigation, or farm machinery.

The spread of Uromyces probus is heavily dependent on specific climatic conditions, particularly high humidity and temperatures between 15°C and 22°C. Moisture trapped on foliage from dew or overhead irrigation is critical for the germination of spores and the establishment of new infection sites.

Effective management requires a combination of cultural and chemical interventions. Preventive measures include rotating crops away from Allium species for several years, ensuring proper plant spacing for air circulation, and utilizing preventive fungicide applications when environmental conditions favor disease development.

• Crop rotation with non-host plants.
• Sanitation by removing infected plant debris.
• Application of approved systemic fungicides.
• Control of weeds that serve as alternative hosts.