A Homegrown NH listener asks:
“What is causing the spruce trees to die? This seems to be a new thing in the last 5 years. What is causing it, and what can be done?”
Emma Erler, Homegrown NH host and lead horticulturist at Squam Lakes Natural Science Center, said the listener is likely referring to the Colorado blue spruce (Picea pungens).
“It is easily one of the most popular conifers for landscaping,” Erler said. “It's a rare yard in New Hampshire that doesn't have at least one of these planted.”
Blue spruce are known for their fast growth rate, a stately form and blue color. These are trees that are native to North America, “but you're not going to find them east of the Rocky Mountains,” Erler said. “And they can have some real issues here in New Hampshire.”
Blue spruce is susceptible to a wide range of insect and fungal disease issues, which are exacerbated by tough environmental conditions.
“We've had a couple of years of drought in summer which are difficult for spruce to contend with,” Erler said. “Then mix in some fungal pathogens, and you have trees that are often dying from the ground up or just don't look very good, and tend to decline over the course of five years.”
Diagnosing the problem
Erler said there are three types of diseases that hit spruces, which can be identified by looking at the symptoms.
Rhizosphaera needle cast causes early needle drop. New needles get infected and typically die within a year, from the ground up. A tree that looks very sparse, with needles only at the very tips of its branches is likely to have this fungus.
On the other hand, unhealthy tips could mean the spruce has tip blight, caused by the fungus Sirococcus conigenus. It typically causes just the very tips of the branch to die back.
Canker diseases caused by Phomopsis shoot blight cause sunken areas on stems or branches that ooze resin. “When you see that, you often end up with dieback, either on individual branches or higher up on the broader tree,” Erler said, “because the tree's vascular system has been damaged.”
Erler said if the tree has canker diseases, you can prune out the cankered branches as long as they are not on the main trunk. Diseased branches should be disposed of or burned.
A tree with needle cast may respond to fungicide. “The downside to fungicides is that they only protect the new growth, the newest needles on the plant,” Erler said, “and they have to be reapplied frequently after rain.”
Erler said trees that are already stressed from environmental conditions are more susceptible to diseases. “If you have a very healthy tree that has plenty of water, plenty of nutrients, and for spruces, plenty of sun and plenty of air flow, they're going to be much more resilient to disease problems than a tree that's planted in a really tough spot with no water, gravelly soil in the shade, not getting a whole lot of wind or air around it.”
Choose another evergreen
Erler said she doesn’t recommend Colorado blue spruce in New Hampshire any longer, but that there are plenty of other evergreens that you can plant.
- Concolor fir (Abies concolor) features soft, flat, blue-green to silvery needles and a symmetrical pyramidal shape.
- Norway spruce (Picea abies) is a good option; it's chosen for Rockefeller Center every year, and has a drooping habit.
- White spruce (Picea glauca) and Serbian spruce (Picea omorika) are also resistant to drought and disease, and can be better choices if you have had issues in the past with a blue spruce.
See you in the garden!
If you have a gardening question for Homegrown NH, email or send a voice memo to HomegrownNH@NHPR.org.
Homegrown New Hampshire is a collaboration between Squam Lakes Natural Science Center and NHPR.
