Posts tagged windthrow

Stressed out trees

The following, from a brochure issued by Iowa State University Extension Service on “The Effects of Flooding on Trees” comes from Linn County Master Gardener Claire Smith, along with a message from Coordinator Bev Lillie, about becoming a master gardener:


Mature, well-established trees are more tolerant of flooding than over mature trees or seedlings of the same species.  If flooding is recurrent or uninterrupted and keeps soils saturated, serious damage to trees may occur. 

Flooding during the growing season typically is more harmful to trees than flooding during dormant periods.  Flood-stressed trees exhibit a wide range of symptoms including yellowing leaves, defoliation, reduced leaf size and shoot growth, crown dieback and sprouts along the stem or trunk.  Symptoms may progress into tree decline and death, reoccur for several years and then eventually disappear, or subside by as early as next year indicating rapid tree recovery. 

Flooding reduces the supply of oxygen to the soil and roots and usually results in growth inhibition and injury to flooded trees.  Deposits of silt or sand as shallow as three inches can be injurious, especially to newly planted trees.  Tree roots also must contend with high concentrations of toxic compounds that accumulate in waterlogged soils.  Strong currents and soil particles suspended in flood waters can erode soil from around the base of trees exposing tree roots.  Exposed roots are vulnerable to drying and mechanical injury and their occurrences may make trees more vulnerable to windthrow. Flood-stressed trees are prime candidates for attack by secondary organisms.  Several opportunistic disease-causing fungi and insects invade trees that are weakened or stressed.  Minimizing additional stress or injuries should be a priority on high value trees for one to three years after flooding to reduce the chance of attack by insects.

            “The best approach to managing flood-stressed trees is to enhance their vigor by following proper tree-maintenance practices and eliminating additional stresses.  Dead or severely cankered branches should be removed as soon as possible.  Aerating the soil, mulching and watering during extended dry periods are recommended tree-care practices that can help enhance vigor, but they are not rescue treatments for severely injured trees.  Trees developing substantial dieback and decline symptoms or those possessing defects that prone to windthrow and structural failure should be removed from the landscape immediately.                                                    

Questions regarding flood damaged or stressed trees, flowers and vegetables can be directed to the Linn County Master Gardeners Horticulture Hotline at the Linn County Extension Office at 319-447-0647.


Contact the Linn County Extension Office at (319) 377-9839 or e-mail Bev at for more information about becoming a Linn County Master Gardener.  Information as well as applications may be picked up at the office, mailed to you or accessed by going to:, then click on Yard and Garden. The deadline for returning completed applications is July 25, 2008.

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