PHYTOPTHORA ROOT ROT ( Phytophthora cinnamomi )
Phytophthora root rot, causes decline and death of Fraser fir. Although this disease is still rated as uncommon in New York, it has caused substantial losses of trees farther south. P. cinnamomi may attack over 900 different species of plants, throughout the world. It is soil-borne and more common in warm or tropical climates.
P. cinnamomi produces several kinds of spores to ensure it's survival and spread. Oospores and chlamydospores (resting spores) usually form within host tissue and have thick cell walls to enable them to survive adverse conditions. These spores may remain viable for several years and may assist in the spread of the fungus over long distances. Swimming spores, (zoospores), are formed when soil is saturated or nearly so, and they are the principle means for spread of the disease within and between root systems.
Infection is thought to be through tender, young growing tips of roots or through minute root wounds. The fungus grows in the vascular system causing plugging of the roots transport cells. The first trees to die from Phytophthora root rot may be scattered in a transplant bed or newly planted in the field. Death of adjacent trees in continually expanding "infection centers" follows and helps to distinguish this problem from other kinds of transplant injury.
The first visible above ground symptoms are often yellowing of plants followed by rapid browning of the foliage. A reddish brown lesion should also be visible in cambial tissue in the root collar region of the plant while similar tissue above the root collar may remain green or otherwise appear healthy.
Heavy soil is conducive to occurrence of problems with P. cinnamomi , so keep Fraser fir out of such sites. Infected trees may not show symptoms for several months to years after infection. If trees begin to wilt and die within 3 years of planting, examine the root collar area for discoloration of the cambium. The fungus should be isolated from suspect trees and grown on selective media to confirm diagnosis, as field symptoms may not be decisive.
Return to Pest Menu