Hello and thank you for contacting Ask Extension. Unfortunately I cannot tell for sure what is going on with your Norway spruce from your pictures but I can tell you some possibilities and then you can look closer at your tree and make a diagnosis. The dead branches are definitely cause for concern. Yes you can cut them back to the main trunk but you may not like the way that looks.

Norway spruce are native to cooler regions. They prefer cold conditions and with exposed (full sun) locations and slightly acidic, well drained soils. Spruces are not well adapted to hot and dry locations and often suffer when planted in warmer climates. They also don’t like heavy clay soils or water logged soils. When exposed to unfavorable conditions they become stressed and are more susceptible to pests and diseases.

It is also possible that your Norway spruce was planted too deep. You normally want to be able to see the root flare around the base of the trunk. If the trunk is buried too deeply, roots may circle around the base or girdle the trunk, restricting nutrient and water flow. This can cause dieback from the base upward. In this article there are some good pictures of a spruce that is planted too deep. https://extension.illinois.edu/sites/default/files/plant_clinic_report_-_spruce.pdf

When your soil is too wet or the spruce is planted too deep it may become more susceptible to Phytophthora root rot. Root rot affects many landscape plants, including spruce and occurs in locations with poorly drained soils. Above-ground symptoms of infected trees include stunted, pale brown needles, followed by uniform browning, starting from the ground up. Roots become soft, brown, and decayed. Spruces that succumb to Phytophthora root rot are typically younger trees that were planted into poorly drained and/or compacted sites.

When planting a new tree, position the tree at the same depth as it was in the nursery container, ensuring the root flare is visible above ground level to prevent suffocation and rot. Piling up mulch around the trunk is also not a good idea. Pull the mulch away from the trunk so that there is no mulch around the base of the tree for about 3-4 inches.

Another possibility is needle cast disease caused by the fungus Rhizosphaera sp. It results in purple to brown discoloration of scattered needles and eventual needle cast (needle drop). Symptoms develop on older needles and on lowermost branches first and then progress upward. Infected needles are cast, but stem tissue remain supple and green; younger needles are not affected. This may explain why the top new growth still looks good.

If you want to know for sure what the problem is I recommend sending your photographs to Michigan State University’s Plant and Pest Diagnostic Lab. Here is their email address: <personal data hidden> They may ask you to send in some samples from your tree. Here is a link to their website: https://www.canr.msu.edu/pestid/ You will want to send at least one picture that shows the entire tree and one that shows a close up of the affected area.

Here are some additional articles you may want to read to help you diagnose what is going on with your Norway spruce.

https://plantpathology.mgcafe.uky.edu/files/ppfs-or-w-24.pdf

https://www.purdue.edu/fnr/extension/phomopsis-dieback-of-spruce/

https://files.dnr.state.mn.us/assistance/backyard/treecare/forest_health/whitesprucediagnosis.pdf