University of Vermont Extension 
Department of Plant and Soil Science

Anytime News Article


THREE SERIOUS TREE PESTS
 
Dr. Leonard Perry, Extension Professor
University of Vermont
 
           
The Asian longhorned beetle, the hemlock wooly adelgid, and the emerald ash borer are three serious tree pests threatening or destroying many hardwood trees in North America.  Learn what they are, watch for them, and if you suspect these insects then report them to your state entomology lab for positive identification (www.nationalplantboard.org/member). 
           
The Asian longhorned beetle is aptly named as it has very long black and white banded antennae.  Adult beetles are large, about an inch to inch and a half long, glossy black with white spots.  It shouldn't be confused with the whitespotted sawyer, the cottonwood borer, or the locust borer, nor injury confused with that of the sapsucker.  The larvae that live deep in the wood, boring and disrupting flow of water and nutrients, cause trees to die.
           
This beetle first was discovered in this country in 1996 on several hardwood trees in Brooklyn, New York.  Since then, beetles have been discovered in other locations near there, New Jersey, Chicago, and most recently in August 2008 in Worcester, Massachusetts.  The beetles were believed to have entered the country in wood pallets and packing material on shipments from Asia.  Although spreading more by natural means, they can be spread through moving firewood or live trees from infested areas.
           
What makes this beetle such a threat is that it attacks many hardwood trees, including maples, birch, ash, poplar, willow, mountain ash, and elms.  If it becomes established in this country it could cause more damage to trees than Dutch elm disease, chestnut blight, and gypsy moths combined.  It could destroy millions of acres of American hardwoods, threatening industries such as maple, timber, and tourism.  Controls consist of both chemicals applied by professionals, and removing all potential host trees up to a half-mile from infested trees.
           
The hemlock woolly adelgid is an aphid-like insect, barely detectable to the eye, which lives at the base of hemlock needles.  Sucking the sap from the needles, it causes them to turn color, die, and fall off.  What you should look for is the white, cottony masses at the needle bases that cover the insect, most prominent in late spring. All these adelgids are female and can lay up to 300 eggs, resulting in up to 90,000 new adelgids in one year.
           
The hemlock woolly adelgid is another introduced or "exotic" pest, native to Asia where it is not a problem.  It was introduced to this country in the 1920's in the Pacific Northwest, and in the early 1950's to the Virginia area.  It lacks natural enemies in America, so has spread from Georgia to Maine on Carolina and Eastern hemlocks.  Since 2002 it has been killing trees in the Smoky Mountains National Park.  In Virginia's Shenandoah National Park, 80 percent of the hemlocks have been killed. 
           
This adelgid spreads naturally by birds and mammals, and also by humans such as in infested nursery stock.  There are quarantines on selling hemlocks from infested areas, so make sure you don't bring hemlocks from such areas on your own.  Controls include injections of pesticides into infested plants, insecticidal oils and soaps, and biological controls that are being developed.
           
The emerald ash borer is a pretty beetle, dark metallic green, one half inch long and one- eighth inch wide.  Larvae spend the summer and fall tunneling under outer tree bark, disrupting sap flow.  This can cause a tree to die in only two to three years.  The larvae overwinter, then adults emerge from mid-May through June, only to lay eggs and start the cycle again.
           
Symptoms of injury include an initial thinning of foliage and crown dieback, larval tunnels under the bark, woodpecker injury as they seek the larvae, and the D-shaped exit holes from the tunnels.  Controls are not yet feasible in the wild, but in landscapes include pesticides applied by professionals.  Firewood should not be moved from infested areas as this is a major means of spread.
           
Only ash trees are attacked, but all 16 native species of ash are susceptible.  This is another invasive pest, believed to have entered the U.S. on wood shipping materials from Asia.  It was first identified in the Detroit area in 2002, and has spread since then to several other Midwestern and Mid-Atlantic states, Ontario and Quebec.
           
With ash a major landscape tree, and valuable in timber and many wood products, a national outbreak could exceed $20 billion in losses.  Already this pest has killed tens of millions of trees in southeast Michigan alone, and similar numbers in other states, resulting in tens of millions of dollars in losses.
           
More information on these pests can be found online such as from the northeastern area US Forest Service website (www.na.fs.fed.us/fhp/). Check on this and other websites for lists and maps of areas where these pests currently exist in order to avoid unknowingly spreading them through firewood and plants.
            

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