Citrus Gummosis

Citrus Gummosis, also known as gumming disease, is a devastating infection primarily caused by soil-borne fungi of the genus Phytophthora, specifically Phytophthora parasitica and Phytophthora citrophthora. The disease severely disrupts the tree's vascular system, leading to limited nutrient transport and decline in overall tree health.

This pathogen affects a wide range of citrus species, including sweet oranges, lemons, and grapefruits. While the infection typically starts at the crown or the graft union where the bark is closer to the soil, it can spread throughout the canopy under high humidity and poor aeration conditions, causing extensive damage to the tree's structural integrity.

The primary symptom is the localized exudation of a viscous, amber-colored gum from the bark. As the disease progresses, the bark in the affected area dries, cracks, and eventually sloughs off. Below the gumming site, the underlying wood becomes stained and necrotic. Foliage becomes yellow and sparse, and in advanced stages, the tree undergoes rapid dieback and may die entirely.

Environmental conditions play a critical role in the prevalence of this disease. Excessive soil moisture, poor drainage, and high humidity are the primary drivers for Phytophthora activity. Mechanical injuries near the rootstock during cultivation facilitate the entry of the fungi into the trunk. The disease is particularly harmful in low-lying orchards with heavy or compacted soils.

Management and prevention practices are essential to minimize losses:

• Improve soil drainage to prevent water accumulation around the trunk.
• Avoid deep planting to ensure the graft union remains well above the soil level.
• Use resistant rootstocks such as trifoliate orange hybrids.
• Apply copper-based fungicides to the trunk and the soil surface during the dormant season.
• Promptly remove and destroy dead plant debris to reduce the overall fungal inoculum in the orchard.