Several fir trees are identified by their pyramidal shape and long, flat green needles. Commonly used as Christmas trees, fir trees are in the pine family and prefer cool, wet climates and grow well in acidic soil. Unfortunately, a number of diseases can affect fir trees.
Annosus Root Rot
Annosus root rot is caused by a fungus. Symptoms of this fir tree disease include yellowing of the crown, conks (fruiting bodies of the fungi) around the trunk and discolouration of the bark and wood with whitish streaks of fungal growth. Annosus root rot is a highly infectious disease that spreads through spores. Management consists of removing infected trees and creating a buffer zone around the remaining trunks.
Powdery mildew affects many indoor and outdoor plants. Several common fungi cause powdery mildew. Signs and symptoms include a powdery white substance on the foliage. Humid conditions in late summer increase the chances of powdery mildew developing. Control this mildew through anti-fungal sprays and removal of diseased parts. In severe cases, entire trees will need to be removed to prevent the continual spread.
Needle cast is caused by multiple species of fungi including Lophodermella, Elytroderma, Rhabdocline, Phaeocryptopus and Rhizosphaera. Fungi are opportunistic pathogens that may enter the tree through open wounds. Warm, humid conditions promote the growth and spread of needle cast. Signs are dark lesions on the needles or spots on the stems and needles. Needles will drop as the disease progresses. Infected wood will have cankers, a form of tissue death in trees, on all or part of the branch. Left untreated needle cast will decimate a fir tree crop. Fungicide sprays are effective treatments for tree farms.