
About this Tree Concern
Swiss Needle Cast is a foliage disease specific to Douglas-fir trees caused by a fungal pathogen. Once the needles are infected with the fungus, they will turn yellow. The affected tree will also shed its needles prematurely, resulting in sparse crowns. Swiss Needle Cast can also lead to stunted growth in Douglas-fir trees.
Although called “Swiss needle cast,” the fungus causing this disease is native to the western United States and was first discovered in Douglas-fir plantations in Switzerland in the mid-1920s where it is considered an exotic pathogen, hence the name. Infection occurs in late spring and early summer when spores are discharged from infected needles. Newer fir needles are more suspectable to infection.
Remediation
Prevention of fungus can be done with good air circulation. Space trees to provide adequate air movement around the trees. Remove weeds from around the base of trees as weeds can create a humid microclimate that favours fungus development. If you do suspect swiss needle cast, a fungicide could be applied as a last resort.