Phytophthora stem and root rot

Phytophthora stem and root rot is a devastating disease caused by oomycetes belonging to the genus Phytophthora. These pathogens are soil-borne and thrive in waterlogged conditions, effectively attacking the root architecture and vascular tissues of host plants, which severely disrupts nutrient and water uptake.

This pathogen has a wide host range, affecting various crops such as lettuce (Lactuca sativa), soybeans, tomatoes, and ornamental plants. When conditions are favorable, the disease can spread rapidly through entire fields, leading to significant economic losses for farmers and commercial greenhouse growers.

Symptoms often begin with stunted growth and leaf chlorosis, progressing to rapid wilting, especially during the hottest parts of the day. A diagnostic sign is the presence of brown, necrotic lesions on the roots and the lower stem, often accompanied by a soft rot of the cortical tissues near the soil line.

Environmental factors are the primary drivers of this disease. High soil moisture, poor drainage, and soil temperatures between 15°C and 25°C facilitate the production and motility of zoospores. These spores are capable of swimming through soil pores and irrigation water to find and infect healthy plant roots.

Effective management requires an integrated approach.

• Improve soil drainage to prevent water stagnation.
• Practice crop rotation with non-host species.
• Use certified disease-free planting material.
• Apply specific fungicides targeting oomycetes during high-risk periods.