Etiology and Management of a Mandarin Rind Disorder in California

Area of Science:

• Plant Pathology
• Horticulture
• Agricultural Science

Background:

• Satsuma mandarin fruit experienced preharvest rind disorder, leading to substantial crop losses in California.
• Symptoms appeared on outer tree fruit, particularly on exposed sides.
• Fungal isolations were inconsistent, suggesting a non-pathological cause.

Purpose of the Study:

• Investigate the cause of the Satsuma mandarin rind disorder.
• Evaluate management strategies for the disorder.
• Determine if the disorder is physiological or pathological.

Main Methods:

• Laboratory studies involved water-soaking mandarin fruit and observing lesion development.
• Field trials tested agricultural summer oil and antitranspirant treatments.
• Efficacy of fungicides and physical rain protection were also assessed.

Main Results:

• Water-soaked fruit developed field-like lesions in laboratory conditions.
• Pre-treatment with summer oil or antitranspirant significantly reduced disorder incidence and severity.
• Single applications post-color break were highly effective; fungicides showed inconsistent results.

Conclusions:

• The mandarin rind disorder is physiological and abiotic, not fungal.
• Water-repellant treatments, specifically agricultural summer oil and antitranspirants, offer effective economic management.
• Protecting trees from rain also prevented disorder development.