Almond hull rot

Almond hull rot is a destructive fungal disease primarily caused by Rhizopus stolonifer, a pathogen that thrives during the fruit ripening stage. This disease specifically affects almond orchards, often leading to significant yield losses and damage to tree architecture.

The primary symptom is the infection of the hull, which turns dark and leathery. Eventually, the infected hulls develop a fuzzy gray mass of spores. As the pathogen colonizes the tissue, it produces toxic compounds that migrate into the spurs and shoots, causing dieback and killing fruit buds.

The development of the disease is highly dependent on environmental conditions, particularly high humidity and warm temperatures as the almonds approach harvest. Infection usually occurs when fungal spores enter the hull through insect-damaged areas or natural physiological cracks in the hull tissue.

The economic impact of hull rot is substantial, as the disease significantly reduces kernel quality and yield. Furthermore, the death of spurs and branches reduces the bearing capacity of the tree for future seasons, requiring extensive pruning to manage the orchard's health.

Management practices focus on cultural and chemical control strategies:

• managing irrigation to reduce late-season tree stress;
• monitoring and controlling insect pests that damage hulls;
• maintaining good orchard sanitation by removing mummy nuts;
• applying appropriate fungicides during the early hull split stage.