Downy mildew of pea

The causative agent of this disease is Peronospora viciae, an oomycete pathogen. It belongs to the Peronosporaceae family and is an obligate parasite of legumes. It is particularly destructive to pea crops (Pisum sativum) globally, thriving in temperate climates where high moisture and cool temperatures prevail.

Symptoms initially appear as chlorotic, yellowish patches on the upper surface of the leaves. Under high humidity, the corresponding underside of the leaf develops a dense, grayish-purple mold. As the infection progresses, these areas become necrotic, leaves wither, and, in severe cases, the entire plant may collapse or show stunted development, significantly reducing its photosynthetic capacity.

The life cycle of Peronospora viciae involves both asexual and sexual reproduction. The pathogen survives the winter in the soil and on crop debris as oospores, which can remain viable for several years. During the growing season, sporangia are dispersed by wind and rain splash, infecting healthy foliage under favorable environmental conditions.

Environmental factors play a decisive role in the disease development. The pathogen requires cool to moderate temperatures (approximately 15–20°C) and high relative humidity. Frequent rainfall and persistent morning dew are essential for the germination of sporangia, making high-humidity regions or wet seasons particularly high-risk periods for pea producers.

Management and control strategies are essential to mitigate yield losses caused by downy mildew. Integrated pest management (IPM) practices involve:

• Crop rotation to reduce the inoculum load in the soil.
• Use of certified, pathogen-free seed treated with systemic fungicides.
• Planting resistant or tolerant pea varieties.
• Ensuring proper field drainage and avoiding excessively high plant densities to improve air circulation.
• Applying preventive or curative foliar fungicides based on local monitoring and disease pressure forecasts.