Haskell County Oklahoma Cooperative Extension Service

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Haskell County OSU Extension
105 SE 3rd Street, Suite A
Stigler, OK 74462

Phone: (918) 967-4330
FAX: (918) 967-3290

Office Hours: 8 am-12 pm & 12:30 pm-4:30 pm 


Haskell County Oklahoma Cooperative Extension Service

Summer Heat Stress Affecting Local Trees

Press Release
August 16, 2010
Brian Pugh, Haskell County Extension Educator, Ag/4-H & CED

Very little rain, 100 degree temperatures, intense sunlight and high winds.  Sounds like a typical Oklahoma summer to most, and yet the trees seem to be taking this recent string of scorching weather worse than usual.  Recently I have received many calls on trees that are prematurely losing their leaves.  It seems to be more apparent on oaks, but is occurring on all species.  So why are these trees dying?  Well, the majority of them are actually not dead!  They have entered a state of dormancy, the same process that happens to deciduous trees every fall.


Trees can go dormant and lose their leaves due to many factors, however the most common is stress.  Many assume that when a tree loses its’ leaves in the summer two things are happening.  First, they believe it is caused by a disease or insect.  And second, most people then assume the tree is dead. 


In reality, this leaf drop is simply a defense mechanism from further injury.  When weather conditions are hot and dry, trees can take up an immense amount of water.  If that water is not in the soil to support the root system the tree shuts down to preserve the moisture needed for continued life.  This means eliminating the loss of water…which happens to be through the leaves.


Couple a few strange weather years in a row with a severe winter (2009-2010) followed by extreme heat and we begin to understand the stress these trees are going through.  Typically, the first trees to show symptoms are rooted in shallow, poor or rocky soil where moisture is generally lowest.  This gives rise to the rows of brown trees evident along ridge tops where the soil is less ideal.  Individual trees that are affected in the middle of an otherwise healthy stand could be a disease indicator, a tree that has seen more stress within the past few years, or indication of a tree growing on shallow rocks.


How can we tell if a tree is in dormancy (still alive) or dead?  We need to conduct the snap-scratch test.  Start by selecting the tip of a twig the size of a pencil.  Grasp the twig and bend it sharply back on itself.  A living limb will bend easily and eventually the stem will split showing moist wood within.  A dead limb will snap cleanly with very little pressure and appear dry within.  The scratch test is another common method.  Use a knife or fingernail to scratch the bark on a young twig.  Living trees will have a green underbark and feel damp to the touch, whereas a dead limb will be tough to scrape and show a brown underbark.


Remember, trees are very hardy and used to dealing with weather extremes.  As conditions return to “normal” these trees will rebuild lost energy and continue on with life.  Although we may not be seeing beautiful fall colors this year, rest assured the majority of these brown trees will return in 2011.


If you’re interested in more information regarding insect, disease or environmental problems in trees or shrubs contact the Haskell County Extension Office at 967-4330.


Oklahoma State University, U.S. Department of Agriculture, State and Local Governments Cooperating: The Oklahoma Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, national origin, religion, sex, age, disability, or status as a veteran, and is an equal opportunity employer.




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