By: Anthony C. Arnoldi, Board Certified Master Arborist WI-0102B
My observations of spruce trees from fall and winter tours indicate that many are struggling to maintain enough needles to look good. In fact, a large number look sparse or somewhat brown. Public awareness of this has also increased as more and more people are calling us for diagnosis of the problem(s).
The reasons for this vary from tree to tree but the over-arching common denominator for all of them is definitely stress from years of inadequate rainfall. It has not been inordinately hot during this stretch, so it catches many people off guard to talk about drought. Nevertheless, to be running 30" of rainfall deficit over the last 6 years is definitely drought. There have been some rainy periods within this time frame, but far insufficient to recharge dry subsoils. Spruce living under these conditions for so long lose feeder roots that die from desiccation. A diminished root system will not adequately supply the needles with water and so needles dry and later die. Thinning results from this needle loss.
Spruce trees weakened from water stress are also more susceptible to their common fungal needle diseases (needlecasts) and fungal branch canker diseases (e.g., Cytospora). They resist them less well so that branch and needle kill is accelerated. Further thinning and browning are seen.
Root rot fungi will take advantage of dead roots in the soil and attack even living roots as alternating too dry/too wet cycles predominate. Off-color needles and further thinning develop.
A few years ago, I wrote an article for this newsletter called Spruce in the Balance (at www.healthytrees.com/newsletters.php, go to 2/10/04). In the ensuing years many spruce worsened and died, and had to be removed if rain or supplemental watering did not provide enough water. It has even been recently brought to my attention that I do not mention often enough that there needs to be supplemental watering done. So let me be very clear: supplemental watering is imperative in most cases in order to adequately meet spruce moisture needs in weeks where less than 1 inch of rain has fallen. Given the depleted state of the subsoil moisture, I recommend erring on the side of watering.
Measures to help replace feeder roots, increase the uptake and drought tolerance of the root system, or counter decline can be prescribed by Wachtel. These help, but will not replace the need for watering. Fungal needlecasts and cankers have their treatments (and are prescribed as necessary), but cannot replace watering.
Therefore, please water as the soils dry again this spring; monitor and measure the rainfall that falls so that you know when to add watering. Treat for the other issues as needed. Your Wachtel certified arborist can help you design the best strategy for recovery of your valuable spruce.
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