Inner Needle Discoloration of Spruce

**Inner Needle Discoloration of Spruce (Picea spp.)**

Host plants: most common on White and Colorado spruce species, but sometimes seen on Norway spruce
Current needle growth has a blue-green color, but older, inner needles lose their desirable color (blue glaucus bloom) and turn pale or even yellow.
This sometimes becomes dramatic and initiates both aesthetic and plant health concerns
Reasons for these symptoms can be from a complex number of conditions, but a compromised root system is typically the underlying cause (often excessively wet soils)
- To determine the cause, first eliminate other causes such as the spruce spider mite stippling systems or dormant oil applications that may have removed the waxy bloom growth on the needles
Compromised root systems result in nutrient deficiencies within the spruce
- The inability of the roots to uptake Potassium (K) or Magnesium (Mg) are often involved
- Highly acidic soil pH can also be a factor
- Excessively dry or wet soils will cause inner needle discoloration
To compensate, the tree creates a self-induced deficiency of potassium (K) to older needles by translocation of K to the newest growth needles
Pale older needles often never fully return back to their previous coloration even after soil conditions are corrected
- Often improves in 2-3 years with new growth

Management:

Fertilization with potassium (K) will not solve the problem because the cause is from root stress and not a shortage of potassium (K) in the soil (usually)
Excessive nitrogen fertilization can make the problem worse
Rework the soil to improve drainage
- This might be difficult in lower areas with high % clay soils
- (Christmas tree farms must select tree species planting sites carefully)

Resources: