Alder powdery mildew

The causal agent of this disease is the fungus Erysiphe penicillata, an obligate biotroph that impacts various tree species. It feeds by inserting haustoria into the host plant's epidermal cells, which allows the fungus to extract nutrients and develop its characteristic surface mycelium.

The primary host for this pathogen is the alder tree (Alnus spp.). While mature trees can tolerate minor infections, young saplings and nursery stock are highly susceptible, which can result in stunted growth and significant losses in plant quality and vitality during the early stages of development.

The symptoms of Erysiphe penicillata are distinct, presenting as a white, powdery dusting on the leaves. As the disease progresses, the white mycelium thickens and may cover entire shoots. Later in the season, small, dark fruiting bodies known as chasmothecia appear, signifying the sexual reproduction stage of the fungus.

Spread occurs primarily through airborne conidia, which are released during periods of moderate warmth and variable humidity. The pathogen thrives in overcrowded plantations where air circulation is restricted, as stagnant air allows the microclimate around the foliage to remain humid, facilitating the germination of spores.

• Remove and destroy all fallen leaves in autumn.
• Ensure adequate spacing between trees to improve airflow.
• Avoid heavy nitrogen application that triggers rapid, succulent growth.
• Use systemic fungicides during high-pressure periods if necessary.

Proactive disease management is essential to prevent severe defoliation. By maintaining good orchard and nursery hygiene and selecting resistant planting sites, it is possible to minimize the impact of this fungus on tree populations and ensure long-term forest health.