Two new fungi associated with spruce needle loss
In recent years two new fungi have been found on spruce trees with needle discoloration.
Trees with symptoms and signs almost identical to Rhizosphaera needle cast were often found to be infected with the fungus Stigmina lautii. In fact it requires magnification of the fungal spore producing structures on the needles to differentiate between Rhizosphaera needle cast and trees infected with Stigmina lautii. This is best done by sending a sample to the University of Minnesota Plant Disease Diagnostic Clinic.
In addition many spruce trees have been recorded with a disorder known as SNEED or spruce needle drop. These trees show yellowing and eventually browning of older needles. By the end of summer, all of the needles on affected branches fall off except the newest needles on the tips of the branches. Although the discolored needles themselves show no signs of fungal infection, the twigs are often covered with tiny black pimple-like spore producing structures of the fungus Setomelanomma holmii. Branches affected by needle drop may be scattered throughout the tree or the entire tree may be affected.
Both fungi have been found on Norway, white and Colorado blue spruce trees. Unfortunately we know very little about the fungi Setomelanomma holmii and Stigmina lautti. These fungi may be new pathogens or they may simply be fungi taking advantage of a tree stressed by drought, heat, poor planting or other environmental factors. Although research on these two fungi is continuing, there are currently no management recommendations for either condition.
The general guidelines listed above about reducing moisture on the spruce
needles can be used to make the environment less favorable to any fungal pathogen.
In addition, reducing stress on the spruce tree by providing water during periods
of drought, mulching the area around the tree, and taking care not to wound the
tree are always beneficial to the overall health of the tree.