Gardening Tips and Highlights Waushara County Master Gardeners

What is Phytophthora root rot?

by Christine Yesko    


Phytophthora root rot is a common disease of Christmas trees including Douglas-fir, balsam, as well as true firs, spruces, and pines. The disease has caused significant problems in Christmas tree production in several states.

In Wisconsin, losses due to this disease are high in Fraser fir Christmas tree production. Symptoms of this root rot are often not observed until it is quite advanced. Above ground, affected trees initially have single branches with needles that turn from green to yellow to red-brown, and remain on the tree. As the disease progresses, trees wilt and die. Below ground, affected trees have root systems with a reduced number of fine, water-absorbing roots. What roots remain are often black and lack white growing points.

This root rot is caused by several species of fungus-like organism (water-mold), that can be involved in Christmas tree root rot can survive for many years in soil and plant debris as thick-walled resting spores that can germinate and directly infect trees. These organisms alternatively during wet periods, certain of these resting spores can germinate to produce swimming spores that are attracted to the roots of Christmas trees and other host plants. Resting spores can be moved from field to field on seedlings and transplants, on soil clinging to field equipment and hand tools, irrigation or flood water, and even on boots and shoes.

If you have trees that you suspect are suffering from the Phytophthora root rot, have them examined by a professional plant disease diagnostician. If the diagnostician confirms root rot, dig up and burn the tree and limit access to the area of the field where the trees were grown. Fungicide treatments will not cure trees suffering from this root rot. Working with a certified Agriculture agent for treatments is advised.

This article obtained from UW-Madison Plant Pathology.