Emerald Ash Borer Threatens Ash Trees


This ash tree is in danger from the emerald ash borer.


They are part of our forests, parks, yards, and city streets.  Or at least they have

been.  But ash trees are now under serious threat from an invasive beetle called the

emerald ash borer (Agrilus planipennis).   It is native to Eastern Russia, northern China,

Japan, and Korea.   The adults are bright green with somewhat darker wings.  They infest

all types of ash trees.   The adults feed on the ash leaves but cause little defoliation.  They

lay their eggs between the bark crevices.  Under the bark is a layer of tissue called the

phloem.  Beneath that is the cambium and under that is the xylem.  The larvae chew

through the inner bark, phloem, cambium, and outer xylem to create long serpentine

galleries.  This disrupts the nutrient and water flow, which starves the tree.  In the fall

they excavate chambers  and overwinter in the outer bark.  In the spring the adults chew

a D-shaped exit hole.

According to http://www.emeraldashborer.info, the beetle is found in over 30 states

and 5 Canadian provinces.   It has caused quarantines in multilple states, cost millions in

removal, and killed millions of trees in North America.

Gwen Kozlowski, the Education Coordinator for the University of Vermont

Extension,  said that 99% of infested trees will die.  Ecosystems will adapt and change,

but there will still be a “significant effect.”   She also said that woodpeckers and the

cerceris wap have been preying on the larve, but it has not been enough to make dent in

the population.

There are two primary control methods for the emerald ash borer.   One is

insecticide and the other is the release of parasitoid wasps that prey on them in their

native range.  In 2007, three of these were released in southern Michigan.   One, Oobius

agrili,  feeds on the eggs  and the other two, Tetrastichus planipennisi and Spathius agrili

feed on the larvae.   In 2015 a fourth one, Spathius galinae, was approved  because S.

agrili did not establish in northern regions.   According to http://www.nrs.fs.fed.us, there have

been “encouraging results,” with reductions in emerald ash borer populations being

correlated with wasp releases.    Kozlowski said  Vermont was  considering  releasing

these wasps in the next two years.

In addition, Kozlowski said insecticide is also being used to counter the spread

in North America, though that takes a yearly application and can be costly.  She also said

this is only effective if the infestation is within 10-15 miles.  She said the insecticide has

proved effective, though there are always some risks.

Kozlowski said the long term plan is to slow the spread as eradication is not

considered a realistic option at this point.   States were formerly getting federal funding

to combat the emerald ash borer, but that funding has decreased.  If people see a tree

they think is infested,  it should be reported to Vermont Invasives or, if not in Vermont,

the  appropriate state agency.







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