Written by  NSW DPI

Phytophthora root & collar rot

Root and collar rots caused by Phytophthora species, a soil pathogen affecting stone and pome fruits, can cause significant tree decline and losses.
Periods of high rainfall and wet soils create the highest risk for Phytophthora.

Disease identification
There are several Phytophthora species that can cause root and collar rot in temperate fruit orchards, and the symptoms are generally the same across the crops.
The first obvious sign of an infection is likely to be leaf yellowing followed by premature leaf drop and a gradual decline in tree health leading to tree death.
This can occur in individual trees or groups typically along a tree row.
Closer inspection around the base of sick trees may reveal the tell-tale wood rot (collar rot) where the tree trunk meets the soil.
Damage
Phytophthora is a water-borne soil pathogen that infects tree roots and crowns causing a loss of root mass, trunk collar rot and significant tree decline.
It is usually associated with poorly drained and water-logged soils. Spores move through the soil in water, hence the disease can be spread by excessive irrigation.
Monitoring
Treatment options are limited, so strategies for prevention and early detection are very important.
Monitor orchards regularly for the early signs of leaf yellowing and tree decline.
Management
Cultural and physical
Cultural control of phytophthora root and collar rot focuses on preventative measures including:
• selecting well drained sites for establishing new orchards
• using resistant rootstocks (options exist for apple and cherry)
• maintaining and improving soil structure
• managing irrigation water to avoid periods of soil saturation.
Biological
Beneficial soil bacteria and antagonistic fungi can play a role in reducing the risk of soil-borne diseases.
Building healthy soil by adding organic matter will help encourage beneficial soil organisms.

Download the Orchard plant protection guide 2020-21

See this article in Tree Fruit March 2021