Phytophthora root and collar rot
Soil pathogens from Phytophthora species can cause root and collar rots. These pathogens affect pome and stone fruit trees and can cause significant tree decline and losses. Periods of high rainfall and wet soil create the highest risk for phytophthora root and collar rots.
Disease identification
Although several species of Phytophthora can cause root and collar rot in temperate fruit orchards, the symptoms are generally the same in all temperate fruit trees. 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, usually along a tree row. Closer inspection around the base of sick trees should reveal the tell-tale wood rot (collar rot) where the tree trunk meets the soil.
Damage
Phytophthora spp. are water-borne soil pathogens that infect tree roots and crowns, causing a loss of root mass, trunk collar rot and significant tree decline. They are usually associated with poorly drained and waterlogged soil. Spores move through the soil in water, so disease spread might be increased with excessive irrigation.
Monitoring
Treatment options are limited, so strategies for prevention and early detection are essential. 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
- good orchard biosecurity practices, such as washing boots in footbaths before entering orchards, can prevent the disease from spreading.
Biological: beneficial soil bacteria and antagonistic fungi can help reduce the risk of soil-borne diseases. Building healthy soil by adding organic matter will help encourage beneficial soil organisms.
Chemical: refer to the Orchard plant protection guide for chemical suggestions.
