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Ash Dieback

Ash dieback (Hymenoscyphus fraxineus) is widespread throughout the UK and very noticeable in Mid Wales. Where possible it is now recommend to leave diseased ash trees as some have been shown to recover. 

Ash dieback, scientifically known as Hymenoscyphus fraxineus, is a devastating fungal disease that primarily affects ash trees (Fraxinus species). It is also commonly referred to as Chalara dieback of ash. The disease was first identified in Poland in the early 1990s and has since spread across Europe, posing a significant threat to ash tree populations.

Key Characteristics:

  1. Causal Agent:

    • The fungus responsible for ash dieback was initially named Chalara fraxinea, but later taxonomic revisions led to its reclassification as Hymenoscyphus fraxineus.

    • The fungus primarily infects the vascular tissues of ash trees. 

  2. Symptoms:

    • Crown dieback: One of the most noticeable symptoms is the progressive dieback of the tree's crown, starting at the top.

    • Wilting Leaves: Leaves exhibit wilting and darkening, and the canopy becomes sparse.

    • Lesions: Diamond-shaped lesions on the bark are often visible, indicating infection sites.

  3. Disease Spread:

    • Windborne Spores: The fungus spreads through airborne spores, which are produced prolifically on infected leaves during the growing season.

    • Long-Distance Spread: Human activities, such as the movement of infected plant material or contaminated soil, contribute to the long-distance spread of the disease.

  4. Host Range:

    • Fraxinus species: The disease primarily affects ash trees, with European ash (Fraxinus excelsior) being particularly susceptible.

    • Other Species: While the main impact is on ash trees, some reports suggest that certain non-ash species may also be infected to a limited extent.

Impact and Ecology:

  1. Economic Impact:

    • Ash dieback has had a substantial economic impact on the forestry and landscaping sectors, as ash is a commonly used tree species.

  2. Ecological Impact:

    • The disease affects biodiversity by threatening ash-dominated ecosystems.

    • The loss of ash trees has implications for various species that depend on ash for food and habitat.

Management and Control:

  1. Pruning and Thinning:

    • Pruning infected branches and thinning the crown may slow down the progression of the disease.

  2. Chemical Treatments:

    • Fungicides can be applied to protect healthy trees and manage the spread of the disease, but their effectiveness may be limited.

  3. Tree Removal and Disposal:

    • Severely infected trees should be removed to prevent further spread.

    • Proper disposal methods, such as burning or chipping, are crucial to reduce the risk of spore dispersal.

  4. Research and Resistant Varieties:

    • Ongoing research aims to understand the disease better and develop resistant ash varieties.

    • Planting resistant species or genotypes is a key strategy for long-term management.

Global Spread:

Ash dieback has spread extensively throughout Europe, affecting ash populations in countries such as the United Kingdom, Ireland, Denmark, Sweden, and others. The disease's presence has raised concerns about the potential long-term impact on the landscape and ecosystems, prompting efforts to manage its spread and find sustainable solutions to preserve ash tree populations. Monitoring, research, and collaboration are essential components of ongoing strategies to address the challenges posed by ash dieback.

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