Kernoviae phytophthora

Pathogen and disease type. Kernoviae phytophthora is caused by the oomycete Phytophthora kernoviae. This pathogen is known for its ability to cause severe tissue necrosis in a wide range of host plants. It is classified as an aggressive threat in forestry and ornamental nurseries, often leading to rapid decline in plant health.

Host range. The pathogen has a broad host range, infecting many ornamental species such as Rhododendrons, Pieris, and Viburnum. Furthermore, it causes significant damage to forest trees, particularly the European beech and various oak species, where it targets the bark and cambium layers.

Symptoms and signs. Typical symptoms include necrotic leaf spotting, shoot dieback, and bark lesions. On trunks, the pathogen often creates distinct cankers that may ooze dark sap, compromising the structural integrity of the plant. Infected trees often exhibit overall wilting, thinning of the canopy, and premature leaf drop.

Development and spread. Phytophthora kernoviae thrives in cool, wet environments. The zoospores are highly mobile in water, spreading through rainfall splash, water runoff, or irrigation systems. The pathogen can persist in infested soil for extended periods, making it a persistent threat in nursery environments and landscape planting.

Harmfulness and protection. The disease is considered a significant biosecurity risk due to its potential to cause landscape-scale mortality. Management relies on strict phytosanitary measures, including the eradication of symptomatic plants, careful site management to ensure good drainage, and the application of protective fungicide treatments where authorized to prevent further spread.