Garden Detective

Why does blue spruce tree look brown?

Garden Detective: What’s causing the needles of this blue spruce tree to turn brown?
Garden Detective: What’s causing the needles of this blue spruce tree to turn brown?

Experts tackle readers’ garden questions.

Q: I have a Colorado blue spruce that I planted back in 1987 and it has always done well. The last two seasons, branches intermittently are turning brown in different areas of the tree. I can not detect any signs of pest or insect infestation and I do not see any indications of squirrels chewing the branches. Does the tree have some sort of a disease? I know they are better suited for higher elevations. I started deep root watering this past summer. Any help would be appreciated as I do not want to lose this old tree.

Joseph Sebastian, Sacramento

Bee garden writer Debbie Arrington: Although they’re considered “evergreen,” Colorado blue spruce trees drop their needles, sometimes more than others. In general, the needles on a Colorado blue spruce last eight to 10 years before finally turning brown and dropping.

The key is whether the tree is replacing those lost needles with new healthy growth. Are the branches still pliable (which is good) or are they brittle (bad)? Do you see new growth? If so, the tree is likely fine.

Spruces can suffer from Rhizosphaera Needle Cast, a fungal disease that causes needles on spruce trees to turn brown and drop, leaving bare branches. This fungus becomes active during long stretches of wet weather, such as we had in 2017. It usually starts near the base of the tree and works its way up. You can check for this fungus by looking at the needles with a magnifying glass. Check a yellowed needle; if you see black spots or lesions on the needle, your spruce may have needle cast disease.

That disease is not necessarily fatal; it tends to attack stressed trees. Trim out the brown branches and protect the healthy growth from infection.

Also if you suspect needle cast fungus, it’s a good time to call in an experienced arborist for expert advice and assistance in restoring your tree’s health.

California’s epic drought had lingering effects on many trees. It takes a tree that size a long time to grow, and a long time to fail. Those brown needles could be an aftereffect of drought as trees are still trying to cope.

Dieback often can be attributed to poor irrigation or a big decrease in available water. Is this tree planted in or next to a lawn? Was irrigation of that lawn severely cut back (or cut off all together)? If your spruce is near that turf, it likely had roots growing underneath the grass and was using some of that water. If irrigation is cut off to the lawn, the tree suffers, too.

In addition, it was an unusually dry winter and many trees needed additional irrigation. Did you irrigate your tree during December and January? It may have needed extra moisture.

Spruces prefer a cooler climate than Sacramento, but can still thrive here. The key is consistent irrigation and good drainage.

Deep and slow watering is the best way to irrigate trees. The idea is to moisten the soil to at least 10 inches in depth under the tree’s entire canopy and past the dripline, the outer edge of the canopy.

Encircle your tree with a soaker hose, starting a foot away from the trunk to avoid crown rot. Wind that hose in a giant spiral around the tree and out several feet past its dripline.

Check the soil with a screwdriver; if you can’t push the tool at least 6 inches into the soil, it’s time to water. A good deep soaking with the soaker hose will take more than an hour. Then, recheck the soil. Apply more water if the soil is still hard.

To help retain that soil moisture, apply a layer of organic mulch (not rocks) under your spruce. That will keep the moisture level more consistent, too.

For more information on care of Colorado blue spruce trees, see the University of California Integrated Pest Management website’s plant notes at ipm.ucanr.edu.

The Bee’s Debbie Arrington is a consulting rosarian and lifelong gardener; darrington@sacbee.com, 916-321-1075, @debarrington.

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