Phytophthora glovera blight

Pathogen and disease type. Phytophthora glovera blight is caused by the oomycete Phytophthora glovera, which acts as a specialized plant parasite. The disease is classified among pseudo-fungal infections that primarily target the vascular system and aerial tissues of host plants. The pathogen can persist in soil and crop debris for extended periods in the form of oospores, which are highly resilient to adverse environmental conditions.

Host plants. The primary range of hosts for this pathogen includes members of the Asteraceae family. It most frequently affects ornamental crops, including various species of Asters, as well as several wild plant species that serve as infection reservoirs in natural ecosystems and field margins.

Symptoms and signs. The disease manifests as chlorotic lesions on the leaves, which eventually darken, turning brown or gray. Under conditions of high humidity, a characteristic white or grayish mold develops on the undersides of the leaves, representing the sporulation of the pathogen. In severe cases, stem necrosis occurs, leading to premature wilting and the total collapse of the plant's vegetative parts.

Developmental conditions. The rapid spread of Phytophthora glovera is favored by high relative humidity (above 85%) and moderate temperatures ranging from 15°C to 22°C. Free moisture on the leaf surface is essential for the germination of zoospores and their penetration into plant tissue through stomata or micro-wounds in the epidermis.

Management and prevention. An integrated pest management (IPM) strategy is required to mitigate crop damage through several key actions:

• Implementing strict crop rotation to avoid planting susceptible hosts for at least 3-4 years.
• Thorough removal and destruction of crop debris followed by deep soil cultivation.
• Utilization of pathogen-free certified seed and planting material.
• Application of copper-based or metalaxyl-based fungicides upon the first detection of symptoms.
• Improving greenhouse aeration to reduce humidity levels in the plant canopy and root zones.