Fungus Infection on Blue Spruce Trees

Occurrence

• Cytospora canker fungus occurs predominantly on blue spruce trees. These affected spruce trees would be found growing in nutrient-poor soil or have become weakened from environmental stress conditions such as drought or excessively hot temperatures. Needle cast afflicts blue spruce trees of all ages, regardless of health or growing conditions. A healthy blue spruce tree can stand up to the fungus better than a weak one and will usually manage to retain its needles for 5-to-7 years, according to Ohio State University.

Appearance

• A blue spruce tree suffering from Cytospora canker fungus will begin to suffer dieback of its lower branches. The fungus gradually spreads upward and begins to infect more and more branches. The branches will begin to lose their needles and cankers will form. The cankers will ooze white-bluish sap. Rhizosphaera needle cast causes the older needles of the tree to fall off. The newer needles that grow on the tips of the tree's branches will remain. The older, infected leaves will display black reproductive spores from the fungus.

Spread

• Cytospora canker invades the tree through pruning wounds or damage that the tree sustains. Contaminated pruning shears can spread the fungus. Rainfall helps spread the fungi's reproductive spores. Rhizosphaera needle cast spreads during the spring months, especially during extremely wet weather. The tree will not begin to show symptoms of the infection until late summer or fall.

Control

• Promptly remove any branches that show signs of Cytospora canker. Cut the branches off next to the tree's trunk and discard. Pruning away the infested branches will often help slow the spread of the disease, but there is a cure. Heavily infested trees must be removed. Treat a tree suffering from Rhizosphaera needle cast with a fungicide. The North Dakota State Forest Service says to treat the afflicted tree with Bordeaux mixture 8-8-100, which is 8 pounds hydrated lime, 8 pounds copper sulfate in 100 gal. of water. Also, use chlorothalonil on the tree. Apply the fungicide in June and repeat 3 weeks later. Continue treating the tree for 2 years.