Distinguishing Phytophthora Root Rot from Psorosis in Citrus

Distinguishing Phytophthora Root Rot from Psorosis in Citrus

A grower asks for the difference between Phytophthora bark infection and psorosis in citrus, and the best treatment for each.

Phytophthora Root and Crown Rot

• Cause: Soilborne water molds (Phytophthora spp.).
• Conditions: Prolonged wet soil, poor drainage, deep planting.
• Symptoms: Gumming on lower trunk, cracking bark, brown necrotic cambium, yellowing leaves, dieback, tree decline.
• Management: Improve drainage, avoid overwatering, plant on mounds or raised beds, remove soil/mulch from trunk base. Fungicides (mefenoxam, phosphonates) can suppress but not cure.

Psorosis (Citrus Psorosis Virus)

• Cause: Virus complex (psorosis A, B, etc.).
• Transmission: Bud grafts, contaminated tools; rarely root grafts.
• Symptoms: Young leaves show yellow flecks, rings, translucent spots. Older trees develop scaly bark, gumming, stained wood, cavities in limbs/trunk. Stunted growth, reduced yield.
• Management: No cure. Remove severely affected trees. Plant certified virus-free nursery stock. Use only virus-free budwood for grafting.

Key Differences

General Citrus Health Tips

• Plant at correct depth (root flare visible).
• Keep area under canopy free of mulch and weeds—bare soil is best.
• Water deeply but infrequently; avoid wetting trunk.
• Consider organic biostimulants (e.g., brix-boosting foliar sprays) to enhance tree vigor and pest resistance.

Accurate diagnosis is essential—consult a lab or extension specialist if unsure.