There could be several reasons for the lower branches dying on your spruce. If the upper branches provide too much shade, the lower branches naturally die off. Also, several diseases can contribute to branch dieback. Cytospora canker is a fungus that attacks spruces and causes branch death. Look for white oozing sap on the dead branches---usually back near the trunk. There is no cure for cytospora; remove the dead branches and cankers to prevent further spread.

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 Another fungal disease, Rhizospaera needlecast, causes the inner needles to die off, leaving only green tips on branches. Over time, this can cause branch death. If examined closely, the brown needles will have tiny black dots, which are evidence of the fungus. You can spray with a fungicide in early spring just as the needles are emerging and again several weeks later to prevent infection. This disease is usually worse where air circulation is poor. Opening up for better airflow may also help reduce disease incidence.