Tree Borers: Destructive Insect Pests

Tree borers and wood boring insects make their homes in the bark, trunks and branches of trees.  Living up to their name, these larvae ‘bore’ in trees, laying eggs and feeding inside roots, trunks and branches and tunneling beneath the bark.  As a result of their activity, trees sustain serious internal damage.  Specifically, injuries restrict the tree’s ability to transport water and nutrients and can ultimately kill the host plant.  Borers are some of the most destructive pests of trees and shrubs.

Tree Species at Risk

Some borers have specific host plants.  Dogwood borer and hemlock borer are examples.  However, others can infest a variety of tree species.  It’s important to note that only a few borers attack healthy trees.  Most infestations occur in trees that are already under stress.  For instance, trees growing in poor soil conditions or those that are subject to extreme weather such as drought.  Further, recently transplanted young plants are targets for infestation.  Maintaining tree health is an important step in preventing infestation from tree borers.  Be sure to fertilize based on soil analysis and water trees properly during dry periods.

Signs of Tree Borer Infestation

In the early years of an infestation, there may be few signs as the pests bore inside the plant, creating irreversible internal injuries.  As infestation progresses, exit holes where adults emerge may be visible in the trunk or branches.  The plant may lose leaves.  In some cases, the beetles will leave a sawdust-like debris, called frass, nearby.

Common Tree Borers

While there are hundreds of wood boring species that are not considered pests, some species pose a serious risk to trees.  Bark beetles are one group that cause widespread damage.  Species like Southern pine beetle are known for the destruction of evergreen trees, but some others like elm bark beetle and oak bark beetles have deciduous trees as their hosts.

Even native species such as bronze birch borer can be problematic, particularly for trees planted in urban and suburban environments.  Though well-known invasive species are often the most infamous of tree borers.  The emerald ash borer is a metallic green beetle that has killed hundreds of millions of ash trees since its arrival in North America.  It is imperative to treat an ash tree or American fringe tree if the emerald ash borer is nearby.  Another example is Asian longhorned beetle.  Attacking a broad range of hosts including maple, horse chestnut, willow, birch and elm, this pest will infest and kill healthy and stressed trees alike.  Being aware of invasive species like these is important to helping prevent further spread and damage.

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