Phomopsis amygdali

The earliest symptom is the formation of small, brown, necrotic spots around buds or small wounds on the bark, which later develop into larger cankers.

As the infection spreads, the cankers encircle the branch, effectively cutting off nutrient and water supply, causing the distal part of the branch to wither and die.

On dead bark, the fungus produces small black dots, known as pycnidia, which become visible and serve as the source of inoculum for subsequent infections.

Almond fruits can also be affected, showing dark, depressed lesions that lead to rot, reducing both the quality and the quantity of the harvested crop.

Cross-sections of infected branches often reveal internal discoloration and reddish-brown wood, indicating the deep penetration of the fungal hyphae.

The disease is caused by the fungus Fusicoccum amygdali (syn. Phomopsis amygdali), a destructive pathogen that specifically targets almond trees and related stone fruit species.

The fungus survives as mycelium or as fruiting bodies (pycnidia) within infected twigs, branches, and mummified fruits left in the orchard throughout the winter season.

During wet weather, spores are released and dispersed primarily by rain splashes and wind, effectively moving the pathogen between trees in the plantation.

The fungus invades plant tissues through wounds caused by pruning, winter frost cracks, insect damage, or natural openings like leaf scars and fruit peduncles.

Once inside the tree, the pathogen colonizes the vascular tissues, producing phytotoxins that obstruct sap flow and lead to systemic necrosis of the affected branches.

Phomopsis amygdali thrives in environments characterized by high humidity, frequent rainfall, and moderate temperatures ranging between 18°C and 25°C.

Spring frosts are particularly dangerous as they create physical cracks in the bark, providing immediate entry points for fungal spores at the start of the season.

Orchards with dense tree spacing and poor air circulation maintain a microclimate of high moisture, which is highly conducive to the rapid spread of the fungus.

Neglected trees, which may be suffering from nutritional deficiencies or lack of proper pruning, exhibit lower resistance to fungal invasion.

Overhead irrigation systems can inadvertently promote the disease by keeping bark surfaces wet for extended periods, facilitating the colonization of tissues by spores.

The disease causes significant branch dieback, leading to a loss of canopy structure and drastically reducing the overall productive capacity of the almond trees.

Infected trees require significant energy to recover and heal, which redirects resources away from nut production, resulting in lower yields per hectare.

In cases of severe infection, entire scaffold branches may be lost, which permanently damages the tree's architecture and requires expensive corrective pruning.

Fruit decay directly impacts profitability, as contaminated nuts are often downgraded or rejected by processors, causing substantial economic losses.

Chronic infestation weakens the structural integrity of the tree, making it susceptible to secondary infections and long-term decline in orchard productivity.

Sanitation is the most critical control measure: all infected branches must be pruned out at least 15 cm below the visible necrosis and burned or buried immediately.

Strict disinfection of pruning tools with alcohol or bleach solutions between trees is essential to prevent the mechanical transfer of fungal spores.

Applying copper-based fungicides during the dormant season and early spring helps to create a protective barrier on the bark against initial spore infection.

• Utilizing systemic fungicides during periods of high disease pressure.
• Maintaining optimal soil fertility to enhance the tree's natural defense systems.
• Painting tree trunks to prevent frost cracks and sunscald damage.

Designing orchards with adequate spacing and implementing proper crown thinning promotes airflow, which significantly inhibits the development of fungal pathogens.