Phomopsis blight of almond

Phomopsis amygdali is a fungal phytopathogen belonging to the kingdom Fungi and the genus Phomopsis. It is recognized as a significant threat to stone fruit production, primarily targeting almond trees (Prunus dulcis) and peach trees, causing severe twig blight, stem cankers, and dieback.

The disease manifests as elliptical necrotic lesions on shoots and branches. As the infection progresses, these lesions can girdle the infected stem, leading to sudden wilting and death of the terminal growth. Affected areas often display significant gummosis, where the tree exudes sap in an attempt to isolate the pathogen, which ultimately weakens the overall structure and productivity of the tree.

The life cycle of Phomopsis amygdali is closely linked to its overwintering stage. The pathogen survives the dormant season as pycnidia or mycelium within dead bark or infected twig tissues. With the onset of warmer, rainy weather in spring, conidia are dispersed by water splashes, wind, and insect vectors, effectively spreading the inoculum to fresh, vulnerable shoots.

Environmental conditions play a critical role in the development of Phomopsis blight. The pathogen thrives in high humidity and moderate temperatures, typically ranging between 18°C and 25°C. Excessive rainfall during the early growing season significantly increases the risk of infection, as wet conditions facilitate both the release of conidia and the susceptibility of plant tissues to penetration.

Effective management requires an integrated approach to minimize disease pressure and protect orchard health:

• Sanitary pruning: systematically remove and destroy infected branches, ensuring cuts are made well into healthy wood.
• Chemical control: apply appropriate fungicides during critical growth stages, particularly during the dormant period and shortly before/after flowering.
• Orchard hygiene: maintain balanced fertilization and irrigation to prevent plant stress and improve general resistance.
• Monitor for secondary pests: control insect vectors that create wounds, as these entry points are essential for fungal colonization.