Downy Mildew on Peas

Peronospora viciae is a pathogenic oomycete that causes downy mildew in various legume crops, primarily affecting plants in the Vicia genus. The disease is commonly known as downy mildew of vetches, peas, and lentils. Here's an informative description of Peronospora viciae, covering its appearance, identification, and management:

1. Symptoms:

• Leaf Lesions: Initial symptoms include the appearance of angular, yellow lesions on the upper surface of leaves.
• Downy Growth: On the undersides of infected leaves, a characteristic downy growth or mold develops. This downy growth is typically white to grayish in color.
• Lesion Expansion: Lesions may enlarge, coalesce, and lead to extensive damage. Severe infections can result in defoliation.

2. Disease Cycle:

• Infection: The pathogen initiates infection through spores (sporangia), which are produced on infected plant tissues.
• Spore Dispersal: Spores are dispersed by wind, water, or other means, leading to the infection of nearby legume plants.
• Germination: Upon reaching a susceptible host, spores germinate to release zoospores, which then infect new plant tissues, completing the cycle.
• Survival: The pathogen can survive between growing seasons in infected plant debris.

3. Identification:

• Leaf Symptoms: Identification often begins with the observation of angular, yellow lesions on the upper leaf surface and the characteristic downy growth on the undersides of leaves.
• White to Grayish Downy Growth: The color of the downy growth is a key identifier.
• Lesion Patterns: Lesions may exhibit angular or irregular patterns on the leaves.

4. Management:

• Resistant Varieties: If available, consider planting legume varieties that are resistant or less susceptible to downy mildew.
• Fungicide Applications: Fungicides, especially those effective against oomycetes, can be applied preventively or curatively. Application timing is crucial, and a rotation of different fungicide classes is recommended to reduce the risk of resistance development.
• Cultural Practices: Practices such as proper spacing, adequate ventilation, and avoiding excessive irrigation can help create less favorable conditions for disease development.
• Sanitation: Removal and destruction of infected plant debris contribute to reducing the source of inoculum.

5. Importance:

• Economic Impact: Downy mildew caused by Peronospora viciae can lead to significant yield losses and reduce the quality of legume crops.
• Global Distribution: The pathogen is present in regions where vetches, peas, and lentils are cultivated.