Ipomoea blight

Causal agent and disease type. The disease is caused by the oomycete Phytophthora ipomoeae. It belongs to a group of plant-pathogenic water molds that cause late blight symptoms. This pathogen is highly specialized and attacks the internal tissues of the plant, leading to rapid tissue death, chlorosis, and rot in both stem and leaf structures.

Susceptible crops. The pathogen primarily targets species within the Ipomoea genus. This includes popular ornamental morning glory vines and the agricultural crop sweet potato (Ipomoea batatas). The fungus is particularly problematic in nursery environments where high plant density and constant irrigation create optimal conditions for the pathogen to thrive.

Symptoms and signs. Clinical symptoms of Phytophthora ipomoeae include water-soaked, dark spots on foliage that quickly turn necrotic. Stem lesions often appear as girdling dark patches that can cause the stem to collapse, leading to rapid wilting of the entire vine. Under humid conditions, a sparse white mycelial growth may appear on the underside of the leaf lesions.

Development and pathogenicity. The pathogen relies on moisture for the production and dispersal of zoospores, which travel via water splash and irrigation systems. Warm temperatures (20–25°C) significantly accelerate the infection cycle. The pathogenicity is high, as the disease can spread throughout a collection of plants in a very short time if humidity is not controlled, leading to complete crop failure.

Control and prevention measures. Effective management of the blight requires a multifaceted strategy focusing on environmental control and chemical intervention:

• Improve greenhouse ventilation to reduce leaf wetness duration.
• Promptly rogue and destroy any symptomatic plants to prevent spore dispersal.
• Utilize appropriate fungicides, such as mefenoxam or copper-based treatments, as directed by local guidelines.
• Avoid overhead irrigation, opting for drip systems to keep foliage dry.
• Implement strict sanitation of all tools and containers used in production areas.