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SUMMER HEAT TOUGH ON PLANTS NOT WELL ADAPTED TO OUR HOT SUMMERS

GARDEN TIPS – written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written Septembe 13, 2015

SUMMER HEAT TOUGH ON PLANTS NOT WELL ADAPTED TO OUR HOT SUMMERS
Two years of record heat is just too much. I am tired of seeing samples of crispy brown plants and being asked the cause of the problem. Quite simply, it has been hot and difficult for plants to survive, especially plants that are not well adapted to our climate.

Several weeks ago I took a look at some local Norway and Colorado spruces that were turning brown and dying. While not always the best clue to the origins of a plant, these spruces’ common names do give us a hint that they may not be well suited well to the hot, dry summer weather of the mid-Columbia. Norway spruce is native to northern and central Europe and prefers a cool, moist, humid climate. Colorado spruce, native to the central and southern Rocky Mountains of the US, is also best adapted to a cool, humid climate.

In their publication on “Spruce Problems” the University of Illinois points out that spruces as a group “prefer locations with acidic, well drained soils” and that “spruces are not well adapted to hot dry locations and often suffer when planted in the warmer regions of the US.” In this publication they also discuss heat injury of spruces, indicating that high temperatures can cause heat damage, especially when the high temperatures are preceded by cool weather. Heat damage on spruces is expressed as browning and dropping of new needles, leaving dead branch tips. After two or three years of this, a spruce is pretty much dead.

Just because spruces are not well suited to our climate does not mean that you can not find healthy spruces growing locally. However, our climate does stress them and make them more vulnerable to attack by a number of pests, like spruce mite, bud scale, and needle miner. I did find spruce bud scale on one of the browning Norway spruces, but the infestation was not severe enough to kill the tree. At least we can be thankful that our dry climate keeps fungal diseases that infect spruce from being a problem here.

Flowering dogwood is another tree that suffers when faced with hot, dry, windy summer weather. In its native habitat, it is an under-story tree that grows in the filtered shade of other forest trees. It grows best in a moist, well-drained, slightly acidic soil that is high in organic matter.

Dogwoods become stressed when planted in full sun and subjected to high temperatures, reflected heat and light from pavement and structures, wind, compacted soil, and poor watering practices. This stress shows up as curled leaves and crispy brown leaf edges. Nevertheless, many of these trees still put on a beautiful display of flowers each spring. To help dogwoods better cope with mid-Columbia conditions, plant them where they will have filtered shade and will not be subjected to a southern-western exposure or drying winds.

Dogwoods and spruce have very shallow root systems, making them more subject to drought and heat stress. It is advisable to keep the roots cooler and moist by mulching the roots with wood chip or shredded bark mulch. Apply a 3 to 4 inch layer of mulch all the way out to the tree’s dripline and beyond. Keep the soil moderately moist, but avoid excessive soil moisture. Be sure to water the spruces during the winter if the weather stays dry and mild.

I hope next summer is a little cooler, don’t you?

SPRUCES NOT WELL SUITED TO REGION

written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

There are a number of lovely spruces available for planting in home landscapes. Unfortunately, spruces aren’t well suited to our arid region with its hot summers and dry winters. Blue spruce is native to the Rocky Mountains and is adapted to high altitudes and cooler seasonal temperatures. The Norway spruce’s name gives us a clue it’s origins. It comes from central and northern Europe (including Norway) and is adapted to a cool, moist climate. Alberta spruce is a variety of the white spruce which is native to Alaska, Canada and the Northeastern United states. Notice the pattern?

Obviously, spruce trees are not well adapted to the climate of the Columbia Basin. When planted in area landscapes they often become stressed. This can result in the failure of the tree to thrive and its gradual decline over time. Signs of stress include purpling of the needles, needle drop, and dieback of the twigs and branches.

In addition to the extreme summer heat of our region, spruces are often subjected to stress from poor watering practices. Spruces have shallow root systems. This makes them vulnerable to injury from watering mistakes. They do best with moderately moist soil. If the soil is too dry, they suffer stress. Intolerant of wet soils and a lack of oxygen, they also suffer stress if kept too wet. Other conditions that affect water uptake and lead to stress include planting the tree too deep, winter drought, girdling roots, changes of grade, root damage due to construction or tillage, and soil compaction.

Because of their shallow roots, spruces situated in home lawns are particularly vulnerable to damage from herbicides (weed killers). Growth regulator type herbicides, such as 2,4 D and dicamba, can cause needles to turn purple and drop or sometimes new growth may stay green and become distorted.

Stress makes spruces prone to attack by a large number of pests. The most common pests attacking spruce in our area are spruce bud scale, spruce spider mite, Cooley spruce gall adelgid, and spruce needle miner. Luckily, diseases that attack spruces in other areas are not a problem here.

One particularly pernicious insect is spruce bud scale. The scale insects are light brown, round and look just like buds situated at the base of new twig growth. They usually go unnoticed until significant dieback of lower twigs and branches occurs. One sign of a spruce bud scale infestation is the tree “dripping sap” which is actually the “honeydew” or sugary excrement of the scale. Another sign is the failure of branched twigs to develop properly, giving growth a “rat-tail” appearance. Spruce bud scale is most commonly found on the lower branches of stressed spruces, especially Norway spruce, in small clusters at the base of the current year’s twig growth.

Spruce bud scale is controlled by applying a horticultural oil or insecticidal soap spray in early summer when crawlers are present. To monitor for the presence of the tiny crawlers use black electrical tape wrapped around the twig with the sticky side out and placed on twigs close to the scales before the crawlers emerge. Dormant oil sprays can also be used for control. The oils are applied during the delayed dormant period… right before the buds open. Be aware that some insecticides, especially oils and soaps, will remove the waxy “blue” coating on blue spruces.

If you have spruces in your landscape, inspect them periodically for evidence of pest problems. To minimize stress, pay careful attention to watering and keeping the soil moderately moist. A bark mulch will help keep the soil moist and protect the roots from temperature extremes. Since spruces are “evergreens” it’s also important to water spruces during mild and dry fall and winter months. Stress is cumulative, so it’s important to give spruces the best care possible and to situate them in the landscape where they’re not exposed to wind or extreme heat.

Published: 10/6/2007 2:34 PM

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