Susan Rose
Grand Junction Free Press Gardening Columnist

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April 4, 2013
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ROSE: What is happening to our evergreens?

Samples have been coming in to the CSU Extension office almost daily of dead and dying evergreens. Driving around Grand Junction, it appears that about one in every four conifers is under severe to moderate stress.

While Austrian pines seem to be suffering the most, they are not alone; Scots, ponderosa, and mugo are coming in with brown or tan needles, often with bands of darker brown and only a little green. Even the occasional Colorado pink spruce sample is showing up. Only the pinyons seem to be largely immune.

With one exception, there is no indication of any disease or insect problems on these samples. They are suffering, quite badly, from severe winter desiccation, the result of two years in a row of severe winter drought.

These two winters could hardly have been more different. A year ago in February and March, Grand Junction was experiencing record high temperatures in the upper 70s. Inevitably, this early season of growth-promoting, dormancy-breaking warmth was followed by a late hard frost. Many of these evergreens, hit at a tender stage, lost all their terminal buds. Their needles began showing the brown banding of drought stress.

This winter you undoubtedly noticed that we were unusually cold. A snowfall on Dec. 19 brought the temperatures crashing down and a temperature inversion set in for a couple of months. Grand Junction wasn't far behind Salt Lake City in adverse air quality. While we humans could head for the hills seeking warmer temperatures and cleaner air, the trees were not so fortunate.

People often want to believe that snow cover equals moisture, but not when the temperatures are so cold. In a process called sublimation, water changes from a solid to a gas without ever becoming liquid. It actually draws moisture out of the soil, not that we had any to speak of to begin with. The result was another very dry winter, but this time it was too cold to water. All we could do was wait until the winds came and the air temperature warmed up on its own, though some residents had creative ideas regarding the use of the orchards' wind machines to blow that nasty inversion out of the valley.

The one exception I mentioned earlier is an insect problem that seems to be fairly unique to our area, at least in terms of severity. Austrian pines in particular are often attacked by black pineleaf scale here, and perhaps because people don't notice it until needles start to brown these infestations often do become quite severe. We don't see this insect infest a healthy, vigorous tree, but we are seeing it on a lot of trees right now.

We know how critical it is to ensure that our woody plants get a good soak in the fall, to go into winter with moist soil around their roots. During extended periods of very dry weather over the winter, supplemental moisture every month or so helps prevent root death from dehydration. This needs to be done on a day when the air temperature is above 32 degrees F.

While we could have attended to this during the winter of 2012, it wasn't possible for us under the severe cold conditions of the 2013 inversion. And our evergreens, which continue to transpire even in the winter, suffered. The drought that didn't kill them off a year ago probably succeeded in many cases this time around. All we can advise people right now is to water, and wait and see.

Susan Rose is a horticulture education specialist with the Colorado State University Tri River Area Extension.


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The Post Independent Updated Apr 6, 2013 03:03PM Published Apr 4, 2013 03:01PM Copyright 2013 The Post Independent. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.