Phomopsis dieback

Causal agent and disease type
The disease is caused by the fungus Phomopsis araucariae (often classified under the Diaporthe genus). It is a fungal pathogen that manifests as a necrotic disease, causing tissue death in conifers. The fungus invades the host through wounds, spreading via pycnidiospores that are released during periods of moisture and high humidity.

Susceptible plants
The primary host for this pathogen is the Araucaria species, most notably Araucaria heterophylla (Norfolk Island Pine). While it is more commonly observed in greenhouse or nursery environments, indoor plants can also suffer from this infection if the environmental conditions are conducive to fungal growth.

Symptoms and signs of infection
Infected plants typically show yellowing and subsequent browning of the needles, which progresses to the dieback of entire branches. Upon close inspection, sunken cankers or lesions appear on the stems and branches. During humid weather, small black structures known as pycnidia emerge through the bark, acting as the primary source of inoculum for further disease spread.

Environmental conditions and impact
The fungus thrives in poorly ventilated, overly humid, and crowded environments. The economic and aesthetic impact is significant; it disrupts the tree's vascular system, leading to permanent branch loss and, if left untreated, the eventual death of the entire plant due to the progression of systemic cankers.

Protection and control measures

• Prune away all infected branches at least several centimeters below the lesion to remove the source of infection.
• Disinfect all pruning tools between cuts using an alcohol solution or commercial disinfectant.
• Apply preventative fungicidal sprays, such as those containing copper or systemic fungicides, during periods of high humidity.
• Maintain proper plant spacing and airflow to reduce moisture buildup on the foliage.