Brown Rot a.k.a Foot Rot Gummosis
Phytophthora on Citrus in the Low Desert

HOST: Citrus: sweet orange and rough lemon rootstocks are very susceptible

SYMPTOMS:

Stunting, nutrient deficiencies, root has brown or black lesions, - The fungus can infect the trunks of any citrus killing the bark and causing a brown gummy discoloration of the cambium and an oozing of dark brown gum. Phytophthora can girdle the tree and causes death in a years time.

CAUSE:

The fungus is everywhere in the soil. It requires moisture to move. As a water born fungus it enters the bark when standing water contacts the trunk of the tree.

MANAGEMENT:
Prevention

• Use resistant rootstock. Sour Orange is highly resistant to Phytophthora however it is vulnerable to a disease carried by the brown citrus aphid which is projected to become a problem in the future. Avoid using rough lemon or sweet orange rootstock.
• Select trees which have been grafted at least six inches above the soil line.
• Control soil moisture

• Remove infected bark and a half inch border of healthy tissue. Treat the wound with a Bordeaux fungicide paste.
• Apply Metalaxyl as a drench, this systemic fungicide will enter roots and kill Phytophthora in the soil and roots.

For additional information and images see AZ1154 Diseases of Citrus in Arizona

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