Olive Tree Problems: Diseases, Pests, and Care

Overview

The olive tree (Olea europaea) is an evergreen native to the Mediterranean, widely grown in warm U.S. regions like California, Arizona, and Texas. It reaches 30 feet and can live for centuries, producing gray-green leaves, white flowers, and nutrient-rich fruit.

Fungal Diseases

• Verticillium Wilt: Causes wilting, thinning canopy, and leaf dieback; severe cases kill the tree.
• Peacock Spot: Thrives in cool, humid conditions, forming blackish-green lesions on upper leaf surfaces leading to premature drop.
• Phytophthora Root Rot: Triggered by excess moisture; symptoms include drooping, discolored leaves.

Bacterial Diseases

• Olive Knot: Caused by Pseudomonas syringae; forms rough galls on branches and twigs, entering through bark wounds. Spread by water; defoliates and kills affected shoots.
• Bacterial Leaf Scorch (BLS): Caused by Xylella fastidiosa; turns leaves brown.

Olive Moth (Prays oleae)

Multiple generations per year: first feeds on flowers, second on fruit (causing premature drop), third on leaves. Flower-feeding generation can destroy the entire bloom.

Other Pests

• Nematodes: Root-knot, citrus, and root-lesion nematodes stunt growth and reduce vigor.
• Sap-Sucking Insects: Olive lace bugs cause rusty yellow spots; various scales attack leaves, stems, and fruit.
• Vertebrates: Rabbits, birds, sheep, and cattle browse leaves and young twigs.

Care for Prevention

Plant in well-drained soil with full sun. Water only when topsoil is dry—olives hate saturated roots. Cool winter temperatures are needed for fruit set. Avoid fall pruning, as new growth may freeze.