Blue spruce needles showing disease symptoms
The Colorado blue spruce is a widely planted ornamental tree. The pyramidal form and its blueish color are the primary reasons for its popularity. It is native to the Rocky Mountains in Colorado and surrounding states. Although most of the planted blue spruce will have the blue color, few trees exhibit it in wild populations. The ornamental trees are grafted from trees with the blue trait, or grown from seeds of populations where the blue color is more common. The seedlings typically do not have the blue needles initially, but it increases as it matures.
This common tree is having problems in our area. You might have noticed that the needles are falling off the lower branches of many trees. This will slowly move up the tree with the lower branches dying. One or two diseases, Rhizopspaera and Stigmina, are the cause this problem. The fungus infects new growth in the spring, but it often takes up to 12 months for the symptoms to be visible. The following spring these infected needles will produce fruiting bodies that will then infect the new growth of that year. Through the summer and fall, the old needles will turn brown or purple and fall off. The fungal fruiting bodies can be seen with a magnifying glass as black dots on the needles. A healthy spruce will keep their needles for around five years, but trees infected with these diseases will only have one year of needles. The disease often starts at the bottom of the tree where it tends to remain wet longer.
To control this disease, you can cut off lower infected branches back to the main trunk to remove some of the infection potential. Fungicides can be applied in the spring as the new growth is emerging to protect this new growth. These treatments would be needed for at least two years. The fungicides act only to protect the new growth from infection. They will not cure the needles that are already infected. Small trees can often be treated by a homeowner, but larger trees may require treatment by a professional.
If the infection is too severe, (at least 50% of the crown is dead) then it is time to consider removal of the tree and replacement. Norway spruce and concolor fir offer similar features and are resistant to these diseases. For more information on these diseases and treatments, contact Phil Woolery at the Purdue Extension Office at (574) 946-3412 or email@example.com. He is a Certified Arborist and would be happy to answer any of your tree questions.