Macrophoma ash dieback

The primary symptom is the necrosis of bark on young shoots and branches, characterized by a brownish or greyish discoloration of the affected area.

Tiny black pycnidia, visible to the naked eye, appear in rows or clusters on the necrotic bark surfaces, indicating the active reproductive phase of the fungus.

Progressive dieback of the tips of branches is common, often leading to the wilting and premature shedding of leaves during the summer months.

In some cases, the disease causes sunken cankers on the stems. These lesions can eventually encircle the branch, causing it to snap or die off entirely.

The aesthetic decline of the canopy is evident as branches die, leading to an irregular, sparse foliage pattern that signifies an underlying health issue.

The disease is caused by the fungus Macrophoma fraxini, which belongs to the Sphaeropsidales order. It primarily colonizes the bark and cambial tissues of ash trees, causing structural damage to the stems and twigs.

The fungus produces small, black, flask-shaped fruiting bodies known as pycnidia on the surface of the bark. These structures serve as the primary reservoir for spore dispersal throughout the growing season.

Infection is typically transmitted by conidia, which are splashed by rain or dispersed by wind onto healthy host tissues, especially where there are existing wounds or natural cracks.

The pathogen can survive in dead twigs and fallen leaves during the winter, serving as a source of primary inoculum for the following spring. It is a highly resilient organism that persists until conditions for growth return.

Biology of Macrophoma fraxini involves penetrating the bark's outer layers to access the nutrient-rich cambium, which leads to the eventual girdling and death of branches.

Development of the disease is highly favored by periods of high humidity and rainfall, which provide the necessary moisture for fungal spore germination and penetration.

Dense plantations with poor air circulation often experience higher disease pressure as moisture remains on bark surfaces for extended periods, facilitating fungal growth.

Temperature plays a crucial role, with the fungus showing optimal activity in temperate conditions, typically ranging from 15°C to 25°C during the growing season.

Trees stressed by drought, poor soil quality, or physical damage from frost are significantly more susceptible to infection by Macrophoma fraxini.

Frequent temperature fluctuations in late winter and spring can cause bark cracking, providing ideal entry points for the pathogen to colonize the tree.

The pathogen causes significant damage in urban landscapes and decorative parks by degrading the visual appeal of ash trees and causing branch mortality.

In forestry, the disease leads to a reduction in timber quality and volume, as repeated infections weaken the tree and stunt its primary growth.

Severe infestations can lead to tree death, especially in younger, vulnerable specimens, which may necessitate large-scale removal and disposal efforts.

The weakening of the tree's health profile makes it more susceptible to secondary attacks by wood-boring insects, compounding the overall damage to the tree.

Economic losses are notable in nurseries, where infected saplings must often be discarded, preventing their sale and distribution for landscape use.

Sanitation is the most effective control measure; all infected branches should be pruned back to healthy wood and removed from the site to prevent further spreading.

Fungicidal treatments, particularly those containing copper-based compounds, can be applied in early spring to protect healthy trees from initial infection.

Maintaining tree vigor through proper irrigation and balanced soil fertilization can help the tree mount a stronger defense against fungal colonization.

Disinfecting pruning tools between cuts is essential to avoid transferring spores from diseased trees to healthy ones during maintenance operations.

• Regular inspection of ash trees during the dormant and growing seasons.
• Proper pruning techniques to remove symptomatic growth.
• Disposing of infected material by burning or burying to destroy spores.
• Applying fungicides during high-risk weather conditions.
• Selecting resistant ash species or cultivars for new plantings.