Phytophthora Leaf and Twig Blight

Phytophthora ilicis

10 host plants

Last updated

Data Maturity Structured

This profile synthesizes data from multiple published sources. Expert field review is in progress.

You'll see leaf and twig blight as browning and dieback of foliage and small branches. This wet-weather disease spreads by water-splash spores. Remove infected material promptly. Improve drainage and air circulation through selective pruning. Avoid overhead watering and reduce leaf wetness. Plant in well-drained locations. This blight is most damaging during cool, wet springs when flower and shoot development is rapid. Monitor plants closely during vulnerable periods.

Control weeds and brambles to help air circulation. Select a site that permits good air drainage. Remove affected tissue promptly, cutting into healthy wood. Improve air circulation by thinning dense growth and avoid overhead watering during susceptible periods. Preventive fungicide applications may help where the problem recurs annually.

Quick Reference

Causal Agent
Phytophthora ilicis
Host Plants
10
Favorable Conditions
Cool fall and winter weather (50-60°F); rainy conditions; poor air circulatio...

Management

Vulnerability Window

Most active during cool, wet fall and winter (October-March in the Puget Sound region). Initial infections begin in late fall on lower limbs. Disease progression continues through winter and into early spring. Less active during warm, dry summers (June-September). New leaf emergence in spring can show infection from overwintered oospores. # Source: PNW Plant Disease Management Handbook

What Triggers Infection

Cool fall and winter weather (50-60°F); rainy conditions; poor air circulation in dense plantings; leaf wounding from wind or pruning; saturated or near-saturated soil; susceptible species (particularly Ilex aquifolium). # Source: PNW Plant Disease Management Handbook - Phytophthora Leaf and Twig Blight

Cultural Controls

  • Control weeds and brambles to help air circulation.
  • Select a site that permits good air drainage.
  • Space and prune trees to permit good air circulation.
  • Remove and destroy fallen leaves and dead infected twigs during the summer.
  • Plant resistant cultivars.
  • Prevent potted plants in nurseries from falling over allowing foliage to touch the ground.

Host Plants (10)