Downy mildew of pea

Downy mildew of pea, caused by the oomycete Peronospora viciae, is a significant foliar disease affecting pea crops globally. Unlike true powdery mildew, this pathogen thrives in cool and moist environmental conditions, making it particularly destructive in early spring or in regions with high humidity.

The host range of Peronospora viciae mainly includes field peas (Pisum sativum) and vetch. The pathogen is highly host-specific, meaning strains that attack peas may not necessarily infect other leguminous crops, though the disease cycle remains consistent across its primary hosts.

Symptoms typically begin on the upper surface of leaves as pale, yellowish-green spots. As the infection progresses, a characteristic grayish-violet downy growth (mycelium and spores) develops on the underside of these spots. If weather conditions favor the fungus, the entire foliage may wither, resulting in severe crop stunting.

Disease development is highly dependent on environmental factors, specifically high relative humidity and temperatures between 10°C and 20°C. The pathogen overwinters as oospores in plant debris within the soil and can also be seed-borne, allowing the disease to initiate new outbreaks in subsequent growing seasons.

Economic damage is caused by the reduction in the leaf area available for photosynthesis, which directly impacts pod development and grain weight. Control strategies for this pathogen focus on an integrated approach:

• selecting resistant or tolerant pea cultivars;
• employing crop rotation to avoid planting legumes in the same field for at least 3 years;
• treating seeds with systemic fungicides to reduce primary inoculum;
• maintaining optimal plant density to improve air circulation;
• applying foliar fungicides at the first sign of infection under high-risk conditions.