CO-Horts Blog

Thursday, October 24, 2019

Are your trees STRESSED?

Posted by: Susan Carter, Mesa County Extension

Stress, we all suffer from it at some point or another.  When we are stressed, we are more prone to get a cold or some other illness.  However, have you ever thought about the stress your plants and trees go through?  For a plant, stress could be planted in the wrong place, incorrectly planted, too much or too little water, storms including lightning, hail, fast changes in weather and long term stress like drought.  The effects on the plants could include something as simple as dropping a few leaves, going into fall color early, or more severely dropping all its leaves and not recouping.  Stress also attracts the bad bugs.
Pinyon pine with Ips damage and drought stress.
Here is Western Colorado; long term drought followed by a severe drought from October 2017-October 2018 has greatly affected our trees.  October to October is considered a water year.  In addition, when you add in incorrect care, boy can the trees suffer.  An example is you see many ash trees planted in parking lot planters.  Did you know ash trees are not particularly fond of heat? Right Plant, Right Place.
Mature ash showing signs of drought stress.
Well, could you put them in a hotter situation and with a limited amount of space for the roots to grow?  And to compound that there may be landscape fabric and rock with drip irrigation, making it hard for the trees to get enough moisture.  Therefore, these ash trees suffer from drought and heat stress attracting such insects as flat-headed apple borer,lilac ash borer and ash bark beetle. Once you get a major insect infestation, it is hard to save or bring back the tree to what it should be.  The ash trees on the western slope may be gone before the emerald ash borer makes it over the mountain.

Then we have our Pinon Pine.  They are native just a little higher in elevation than the Grand Valley.  They can live up to 800 years and produce the pine nuts that we eat.  Many animals depend on this tree and typically, it is a wonderful smaller evergreen for drought tolerant landscapes.  It prefers a deep soak about once a month.  In nature, the long-term drought have made them very susceptible to Ips beetle, also called Engraver beetles from the pattern that they leave from their eating under the bark.  When a tree is healthy and has enough water, but not too much, it can push the beetle out with its pitch.  But when stressed it gets attacked and more and more beetles come up to the thousands.  Once this has happened it takes a little while to turn brown, but once it does it is too late.  Since we water, we often do not see issues that occur in the wild happening in our landscape.  Unfortunately, numbers of Ips are so high and our landscape trees are stressed, so we are rapidly losing pinon pines in the landscape.  
Pinon pine with Ips damage.
Adult Ips beetle.
So what can you do?  Well if your pinyon is still green, treat the trunk with a pyrethroid spray in spring and fall. Then water properly!  What does that mean?  Well, we are great at watering trees when we first install them.  Then we forget to MOVE the water with the root growth.  The drip at the trunk is only good for the first 4-5 months, and then the roots want to grow beyond that.  Pinyons are one of the few trees that has a modified root system of part taproot but mostly spreading root.  So as wide as the crown of the tree, multiple by at least two (2) to get where the roots occur.  In rocky areas, this is even greater distance.  Therefore, a 10’ wide tree has a minimum of a 20’ wide root system. 
Pinon pine in Glade Park with drought stress.
In addition, the majority of the root system is in the top 12-18” of soil.  So wet that entire mass of root system.  Do not plant drought resistant trees in a lawn, which has different watering needs.  Don’t use weed fabric; it blocks movement of air and water and causes roots to rise and girdle making them less drought tolerant.

If you plant new trees, plant a diversity of trees.  Plant them in the right place that they love.  Follow our planting guidelines.  In addition, do not forget to move the water.

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