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Horticulture

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Heat, Drought Damage in Spruce

by
Sarah Browning, UNL Extension Educator

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Have you gotten tired of talking about drought yet? Well, unfortunately more effects from this summer’s hot, dry conditions are being seen; this time in a tree we traditionally have considered very drought tolerant- spruce. Many homeowners have found spruce needles turning brown and falling, leaving behind branches completely bare on trees that were completely filled-out and healthy this spring. And not just young or recently planted trees have been affected. Large, mature, well-established trees, 15 to 20 years old or more are showing damage, too.

Look-a-likes

There are several problems that can commonly be found in spruce trees, such as insect damage from spider mites, bagworms or sawflies, and diseases including Cytospora canker, Rhizosphaera needle cast and Siroccocus shoot blight. Each pest causes specific damage or symptoms on trees, such as yellow pin pricks on needles affected by spider mites and black fungal structures on needles killed by Rhizosphaera needle cast.

We also don’t want to confuse this problem with the process of natural needle drop that evergreens experience each fall, shedding the oldest, inner needles on a branch, and leaving behind healthy green growth on the branch tips.

Symptoms of Drought Damage

Trees damaged by drought don’t show any of these symptoms. Often the first sign of trouble is a change in needle color, from a healthy medium green to light green, followed quickly by light pinkish-tan before the needles fall. In early stages, only the newest growth at branch tips may be affected, but as drought continues entire branches or whole trees may die. Affected branches can be located anywhere within the tree- top, middle, or bottom- and may be spaced randomly throughout it.

If a tree wasn’t inspected regularly during the summer, a homeowner may find that suddenly their healthy tree has several bare branches. Discolored needles fall from affected branches with the lightest touch. Branches and needles both are brittle and dry.

Differences in severity of damage is evident among evergreen species, with Norway spruce (Picea abies) and Douglas fir (Pseudotsuga menziesii) showing the most damage. Colorado spruce (P. pungens), both the green and blue forms, shows less damage.

Since needles are falling now, it’s tempting to think the damage happened recently. It actually began several weeks ago, possibly in August when summer’s hot conditions were at their worst. During this time of extreme heat, trees lost large amounts of water through the needles every day; more than could be replaced by root absorption at night. Drought complicated the situation, since little soil water was available. Damage occurred slowly as trees lost water day after day, resulting in needle, twig, and branch death.

Management

Drought stress strongly predisposes trees to attack by boring insects, bark beetles or infections by Cytosphora or other fungal cankers. If you have similar damage on your spruce trees, it’s important to keep these fall and winter watering tips in mind.

  • Keep trees well watered this fall, allowing them to rehydrate. Monitor the amount of weekly precipitation we receive, whether rain or snow. Water whenever we do not receive an inch of precipitation per week throughout fall and winter when soils are not frozen. A deep soaking every two weeks is adequate for most trees in unirrigated landscapes with clay soil. Deeply water trees with a slowly running sprinkler left in place long enough to moisten the soil 18 to 24 inches deep. Apply the water slowly so it can soak in and not run off. Move the sprinkler to a new location until the entire area beneath, and a several feet outside the tree's drip line has been watered.
  • Spread a 3-4 inch thick layer of coarse organic mulch, like wood chips in a 3 to 6 foot diameter area around the base of the trunk to blanket the soil. This helps conserve valuable moisture and minimizes harmful winter temperature fluctuations around the tree's roots.

Dry, brittle branches with no remaining live foliage, and dead brown buds can be pruned away. If you question whether a branch is alive, wait until new growth begins in spring to complete your clean-up of dead branches. Trees that are completely brown, with no living needles should be removed.



This resource was updated December 2013 and appeared in the Lincoln Journal Star Newspaper Sunday edition. For information on reproducing this article or using any photographs or graphics, read the Terms of Use statement

University of Nebraska-Lincoln Extension in Lancaster County is your on-line yard and garden educational resource. The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office


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