The Colorado blue spruce, or Picea pungens, is a favorite choice for Christmas trees as well as a robust and substantial addition to a landscape. While this tree grows up to 75 feet high if left unchecked, it is susceptible to infections and pests that can damage and even destroy it.
Rhizosphaera Needle Cast
Caused by Rhizoshpaera fungus, needle cast is a disease that causes an inordinate amount of needles to shed from the blue spruce. This needle shedding can happen even during the growing season and can damage a developing plant. Signs of needle cast include needle shedding and black spots on the needles of the blue spruce. Chlorothalonil fungicides can help control the Rhizosphaera.
Another disease that afflicts the Colorado blue spruce, Cytospora canker is also caused by a fungus. Canker appears as open lesions on the trunk and branches of the tree. Cankers are even more dangerous than other fungal diseases because the open wounds caused by the disease make the tree susceptible to predators. Treat trees suffering from Cytospora canker by cutting out infected tissue from the open wound with a knife and rubbing the surface of the wound with ethyl alcohol.
Lirula Needle Blight
Causing extensive die back even in established trees, Lirula needle blight is a fungal infection. This disease manifests itself as browning and dead needles along the branches starting from the center of the branch and working its way out to the tips. Again, fungicides such as Chlorothalonil can prevent lirula needle blight.
Tiny pests, such as the spider mite, can also damage a Colorado blue spruce. This tiny mite feeds on new growth and buds. Spider mites cause needles to brown and fall from their branches. Insecticides such as carbaryl can control and prevent spider mites.
Spruce Needle Miner
Affecting many spruce trees including the blue spruce, the spruce needle miner weaves silky white strands around the spruce tree’s branches. This miner is a moth caterpillar and will feed on the needles as well as the new growth of the tree. Carbaryl is an effective chemical insecticide for controlling leaf miners.
Yellowheaded Spruce Sawfly
Consuming older needles in their youth and working their way to the new growth as they mature, yellowheaded spruce sawfly larvae will damage Colorado blue spruce trees during their active season from May through mid July. Pesticides such as acephate and carbaryl are effective in controlling sawfly issues.
- North Dakota State University: Colorado (Blue) Spruce
- The Ohio State University: Rhizosphaera Needlecast on Spruce
- Colorado State University: Cytospora Canker
- University of Minnesota: Lirula Needle Blight
- UC ICM Online: Spider Mites
- The Ohio State University: Spruce Needleminer
- University of Minnesota: Yellowheaded Spruce Sawfly
- Nebraska State Government: Chemical Control of Common Forest & Shade Tree Pests