Sunday, August 15, 2021

Spruce Blues and Wet-Weather Woes

blue spruceWhen I’m asked to diagnose tree problems, folks naturally want the remedy. Sometimes the only solution is tree removal; other times it’s a cable brace, pest management, corrective pruning or fertilizing. But increasingly, the diagnosis is climate change. If anyone knows how to solve that through an arboricultural practice, please let me know. 

With rising temperatures, a novel weather pattern has taken hold with longer and more intense dry and wet periods. In 2012 many areas had the lowest soil moisture ever recorded. Nonstop rain in 2013 led to flooding and farm disaster relief. A drought in 2016 set more records in some places, and catastrophic flooding hit in 2017. Drought followed in 2018, and 2019 was another massive flood year. Prolonged dry spells cause root dieback, weakening trees for several years afterward. But unusually wet seasons are just as bad for trees.

(Photo at left: Mundhenk, CC BY-SA 4.0, via Wikimedia Commons)

About twenty years ago I noticed a rise in the incidence of a spruce ailment called Rhizosphaera needlecast, arborist-speak for “spruce needles turn brown and fall off.” This native fungal pathogen was always considered weak and opportunistic. Historically, it only showed up when spruces (and rarely other conifers) had been planted too densely, allowing the needles to remain wet long enough for this wimpy microbe to enter foliar cells. The answer was to thin out the trees to make space between them so air could circulate, and remove spore-infested dead branches. This remedy was kind of like drinking lemon-honey tea and getting lots of rest until your cold clears up – simple, but it usually worked. 

I was curious as to why Colorado “blue” spruce (Picea pungens) was much harder-hit than other species. The reason has to do with its origins: Colorado spruce is adapted to an arid environment. In fact, its foliage is actually green, and the blueish appearance is due to a heavy layer of wax (which you can rub off) that the trees make to retain moisture. So when a pathogen like Rhizosphaera that needs copious moisture for extended periods to become infectious meets a tree designed to hold moisture, an unhappy relationship ensues. 

colorado blue spruce

With more and more calls coming in about this issue, by 2010 I was advising people to only plant Colorado spruce on open, preferably elevated, sites. But when I began to see needlecast disease in windy, full-sun environments, it was clear a “new normal” had emerged – extended wet periods were allowing pathogens to access trees in open, ideal settings, not just those packed too tightly together. 

Cornell’s Plant Pathology Lab was also dealing with higher numbers of samples, and they identified Stigmina needle blight and Cytospora canker, native pathogens that work in concert with or in place of Rhizosphaera to cause needle drop. The rate of disease advancement can potentially be slowed through a series of three fungicide applications each spring. For a mature tree, this is likely in excess of $1000 per year for the remainder of the tree’s life, an expense few can afford.

Around 2017, many Cornell Extension Educators began to advise against planting Colorado spruce, a position I heartily endorse. White spruce (Picea glauca), once deemed moderately resistant to needle disease, is now being severely affected as well. Fortunately, there’s still a contender in the ring: Norway spruce (Picea abies). Every native conifer species, whether hemlock, balsam, white pine or spruce, all face relatively new and very significant threats. As much as I prefer native species, I think it’s important to plant more Norway spruce – we need the diversity. 

I recommend planting a broad range of tree species, but only those which are still appropriate for our climate. To paraphrase some good marriage advice I once got about choosing between happiness and needing to be right, “Do you want to be happy, or do you want a blue spruce?” Let’s leave them in Colorado.

For more information, see:

https://ecommons.cornell.edu/bitstream/handle/1813/60599/BranchingOut_Spruce8-13.pdf?sequence=1&isAllowed=y

Paul Hetzler is an ISA Certified Arborist and a former Cornell Cooperative Extension Educator. 

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Paul Hetzler

Paul Hetzler has been an ISA Certified Arborist since 1996. His work has appeared in the medical journal The Lancet, as well as Highlights for Children Magazine.

You can read more of his work at PaulHetzlerNature.org or by picking up a copy of his book Shady Characters: Plant Vampires, Caterpillar Soup, Leprechaun Trees and Other Hilarities of the Natural World




5 Responses

  1. MITCHELL EDELSTEIN says:

    I’m noticing Tamarack (Larix laricina) trees in swamp areas (wetlands) are starting to turn yellow. This is months ahead of usual. Is this due to this Summer’s weather pattern?

  2. nathan says:

    my blue spruce has been having similiar issue, i put thick layer of dark sand around tree for 30 feet, making a hotter drier micro-climate around tree base. so far its working . the extra solar heat and drying sand seems to work.

  3. Ray Mainer says:

    Our Serbian Spruce is a lovely tree in our yard. It suffered for many years from Cytospora canker (or I am told that’s what it was). It seems to have out grown it. Maybe summers are a little dryer for it is doing well.

    I see many blue spruces with dead branches. It’s just too damp here.

  4. geogymn says:

    In the Mohawk Valley Blue Spruce are succumbing to the disease every where you look. I’ve seen several times a weaken BS fail in a strong wind. It forced me to get rid of the three 60 year old BS that shielded my home from weather and people. It was a tough decision.

  5. Vanessa Banti Vanessa B says:

    We have a blue spruce next to our apartment in Mass that I am amazed has survived our climate. Likewise with the hemlock at the end of the street. (Local hemlocks are really suffering from HWA). I am happy that some trees seem to be surviving, but Paul is right – getting healthy long-term survivors is most important. I have said before, but I absolutely *adore* the conifers of the ADKs. Let’s work to help them survive as long as possible.

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