Alder phytophthora

Phytophthora uniformis is a destructive oomycete pathogen recognized as a cause of alder phytophthora, a disease that threatens alder populations across various regions. This pathogen is closely related to other Phytophthora species and specifically targets the vascular system of trees in the Alnus genus, leading to fatal damage.

The primary host for this pathogen is the common alder (Alnus glutinosa). It impacts both young saplings in nursery environments and mature trees in forests or riparian habitats. The disease is particularly dangerous because it often goes unnoticed until significant crown decline has already occurred.

Key symptoms of the infection include the formation of dark, oozing necrotic lesions on the bark at the base of the stem. When the bark is removed, the inner tissue shows characteristic reddish-brown discolouration. Foliage typically becomes sparse, smaller than normal, and may show premature yellowing, reflecting the reduced efficiency of the tree's root system in taking up water and nutrients.

The development and spread of Phytophthora uniformis are heavily influenced by moisture availability. The pathogen produces motile zoospores that navigate through water-saturated soils to reach the roots of healthy trees. Consequently, riparian zones and areas with heavy, poorly drained soil are at the highest risk of infestation, especially during periods of flooding or high rainfall.

Managing this disease is challenging, making prevention the most critical strategy. Effective control methods include:

• Sourcing nursery stock only from certified disease-free suppliers.
• Ensuring proper soil drainage in planting sites to prevent water stagnation.
• Strict sanitation protocols for equipment used in forest management.
• Quarantine measures for regions where the pathogen is known to be active to prevent further spread.