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Insects and Disease

Insects and Disease


Insects and disease are of a primary concern to the tree farmer.  Combined, these elements destroy more timber each year than all other factors combined.  Each type of tree has its own disease  and/or insect enemies.  Insects and disease attack weaker trees in a forest so it is important to keep your forest in a healthy condition.  If insect or disease conditions increase, this can lead to a widespread outbreak and a high mortality rate.  If possible, the trees that are infected or under attack should be removed from the forest.  This can be done during weeding, thinning, or harvesting operations.  Having a diversified forest also helps keep widespread outbreaks under control.  Past outbreaks of the spruce budworm happened in stands that had high numbers of spruce and fir.  This created fertile ground for the budworm to become an epidemic.


You must walk through your forest and inspect it for insect and disease problems on regular basis.  You must also know what to look for as you are inspecting the various trees.  The trees will show signs of the disease in most cases.  If you recognize or suspect your forest is under attack, you should promply contact a forester for further assistance.  Some obvious signs to watch for include:


1.  The bark will show signs of damage or cankers will ooze sap or pitch.


2.  Needles that are short or have damage or bumps on them.


3.  Small leaves or leaves that look sickly or appear curled and shriveled.


4.  Wound holes or other evidence of insects feeding on the trees.


5.  An unusual amount of a particular insect on a tree. 


Some of the common insects that can damage and kill your trees include:


White pine weevils attack eastern white pine and spruces.  They kill the tops of the trees.


Birch leaf miners attack gray and white birch.  They discolor leaves and slow growth.


Spruce gall aphids attack norway and white spruce.  They create "pineapple" type gall branches.


Spruce budworm attack spruce and balsam fir.  They defoliate the trees.


Gypsy moths attack hardwoods and softwoods.  The defoliate the trees.


Balsam Wooly aphids attack balsam fir.  They kill the trees or severely weaken them.


Tent caterpillars attack hardwood trees.  They defoliate the trees.


Saddled prominent attack hardwood trees.  They defoliate the trees.


Oak twig pruners attack oaks.  They kill twigs and branches.


Hemlock woolly adelgid attack hemlocks.  They seriously weaken and kill the trees.


Some of the common disease elements that can damage and kill your trees include:


Dutch elm disease attacks American elm and kills the tree.


Nectria and strumella cancers attack many hardwood trees.  They damage the trunk and can kill the trees.


White pine blister rust attacks eastern white pine.  It damages the trunk and kills the trees.


Anthracnose attacks hardwood trees.  It kills the leaves and slows growth.


Needle blight and needle cast attack softwood trees.  It kill needles and slows growth.

​Maine Forestry

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