Phytophthora root rot of maple

The causative agent of the disease is the oomycete Phytophthora acerina. This soil-borne pathogen specializes in attacking the root system and the root collar of maples, disrupting the plant's ability to transport water and essential nutrients throughout the vascular system, often leading to rapid tree decline.

The primary host for this pathogen is the genus Acer (maple). While it affects various species, young trees and saplings in nursery environments are particularly vulnerable due to their sensitivity to root damage and the often intensive irrigation practices used in commercial production.

Symptoms of the infection include chlorosis, foliage wilting, and thinning of the canopy. A critical diagnostic sign is the presence of brown, sunken lesions or necrotic areas on the bark at the base of the trunk or on the main structural roots, which may show exudation during periods of high humidity.

The development of the disease is highly correlated with environmental factors such as saturated soils, poor drainage, and cool to moderate temperatures. Since the pathogen produces persistent oospores, it can survive in the soil for several years, waiting for favorable conditions to infect susceptible root tips.

Effective management and protection strategies include:

• Selection of well-drained planting sites to avoid waterlogging.
• Rigorous inspection of nursery stock to prevent the introduction of the pathogen.
• Implementation of strict sanitation procedures for tools and equipment.
• Use of fungicides containing fosetyl-aluminum or metalaxyl as part of a preventive program.
• Improvement of soil aeration and avoiding overhead irrigation where feasible.