Cytospora actinidiae

Cytospora actinidiae is a devastating fungal pathogen that causes a necrotic disease of the bark and cambium in actinidia (kiwi) plants. This pathogen disrupts the plant's vascular system, preventing the transport of water and nutrients, which ultimately leads to the rapid wilting and dieback of affected branches or entire vines.

This disease primarily attacks various species of the Actinidia genus. It is opportunistic in nature, typically infecting plants that are already stressed by environmental factors such as severe frosts, sunscald, drought, or physical damage caused by improper pruning and maintenance. The fungus gains entry through these vulnerable spots on the plant's bark.

Symptoms of the infection include darkened, sunken lesions on the bark surface. As the infection progresses, the infected tissue becomes brittle and cracks. A characteristic sign of the disease is the development of small, black, erupting fungal structures known as pycnidia, which emerge through the dead bark and release spores to further spread the infection.

The spread of Cytospora actinidiae is highly dependent on climate conditions. High humidity, frequent rainfall, and mild temperatures provide the perfect environment for spore germination and colonization. Wind and splashing water act as the primary vectors for dispersing spores onto healthy tissues, potentially leading to rapid orchard-wide outbreaks.

Management and prevention require a strict set of agricultural practices:

• Regular removal and burning of dead or infected branches to reduce inoculum pressure.
• Applying protective paint or copper-based fungicides to all pruning cuts.
• Maintaining vine vigor through proper irrigation and balanced fertilization.
• Whitewashing trunks to protect the bark from thermal damage and sunscald.
• Sterilizing all pruning tools with disinfectant solutions between trees.