EMERALD ASH BORER – NOT THE FIRST INVASIVE THREAT TO MASSACHUSETTS TREES
With the discovery of Emerald Ash Borer in Dalton, MA in August of 2012 the Ash trees in Massachusetts are on the verge of a tree-killing wave that has been faced by other tree species over the years.
Emerald Ash Borer was first discovered in Michigan in 2002. Since its arrival from Asia the insect has spread to 17 other states and is responsible for the death of untold millions of Ash trees. Controlling Emerald Ash Borer, and removing Ash trees that are beyond saving, has put a strain on already tight homeowner and municipal budgets.
There are several key indicators to look for that can help determine if your Ash tree is being attacked by Emerald Ash Borer:
Thinning of the upper tree canopy.
Sprouts growing from the base of an Ash tree.
D-shaped holes on the tree trunk or tree branches.
Increased woodpecker activity – look for bark on the ground under the Ash tree.
Tree services use a variety of techniques to save Ash trees from Emerald Ash Borer including tree spraying, insecticide soil injection, and tree trunk injection. The first step, of course, is to have an arborist inspect your property to determine if you have any Ash trees. Then you must decide if you want to save your Ash tree. Emerald Ash Borer is quite aggressive and trees that are not protected will be killed.
Of course the Emerald Ash Borer is not the first invasive pest to plague Massachusetts' trees. In 2008 one of the most damaging invasive insects, the Asian Longhorned Beetle, was discovered in Worcester. An insect eradication effort was soon underway that resulted in the removal of thousands of landscape and forest trees. With an appitite that spans many more tree species than the Emerald Ash Borer the Asian Longhorned Beetle is known to attack:
Before these newcomer insects Massachusetts trees faced a fungal foe in the form of Dutch Elm Disease. Contrary to popular belief, technically, there is not a tree called the Dutch Elm and, although the disease was brought to the U.S. on infected wood from Europe, the disease originated in Asia. The disease is called Dutch Elm Disease because the actual pathogen was discovered by a Dutch scientist.
Dutch Elm Disease is spread by a couple species of bark beetles that feed on our native Elm trees. Feeding damage from the beetles is minimal, but the passage of the disease to the tree results in deadly consequenses. If you are lucky enough to have a native Elm in your landscape treatments to control Dutch Elm Disease are available. For most trees arborists use fungicide trunk injections to save Elm trees. It should be noted that while fungicide trunk injections work most of the time, they will not prevent Dutch Elm Disease transmission through root grafts.
Another tree disease that was inadvertently brought to the U.S. was Chestnut Blight. At one time the American Chestnut may have represented 15-25% of the total number of trees in the forests of the Eastern United States. The fast-growing American Chestnut often reached heights of 90 feet with straight trunks 3-4 feet in diameter. Highly valued for both its wood and fruit, the American Chestnut was one of the most important trees to the early European inhabitants of the United States.
No cure has been found for Chestnut Blight although research and cross breeding to develop resistant cultivars is ongoing. Stump sprouts from American Chestnuts can occasionally be found in the forest, but they are usually killed off by Chestnut Blight before they produce nuts.
Another insect-disease complex affecting trees in Massachusetts is Beech Bark Disease. This disease, which only affects Beech trees, was discovered in Maine in the early 1930's and has been slowly moving southward. While other tree diseases are carried on insects and passed to a tree during the feeding or egg laying process, this is not the case with Beech Bark Disease. The non-native Beech Scale creates wounds on the bark of Beech trees as they feed. The open wound allows one of two species of Nectria fungi to infect the open wound.
Beech Bark Disease is a slow killer – taking up to two decades to wipe out a Beech forest. Research is continuing on the best way to control Beech Scale. If you have a Beech tree in your landscape it should be regularly inspected by a qualified arborist and possibly treated if Beech Scale insects are found.
Possibly the first invasive insect released upon the trees of Massachusetts was the Gypsy Moth. This insect was intentionally brought to the Boston area in 1869 by a French scientist in an attempt to establish a silkworm industry in the United States. The Gypsy Moths escaped captivity when the enclosures that held the insects were overturned in a storm. A short list of trees that Gypsy Moth will feed on includes:
The Gypsy Moth is now well established throughout most of the United States and feeds on a wide variety of trees and shrubs. The population is cyclic and trees should be protected when the population peaks. Most tree services use tree spraying as the means to control Gypsy Moths. Trees that are not protected may be completely defoliated and if this occurs more than once it may cause the tree to die.
What makes invasive insect and disease pests so damaging is that our native trees and shrubs have no natural defenses to protect themselves. Occasionally, environmental conditions inhibit the establishment or spread of invasive pests, but this is all too rare. In the meantime we must rely on scientists to develop and test control options and for arborists and tree services to provide the treatments to our trees. This takes time and in the process forest and landscape trees are lost to the invaders. Meanwhile, we protect our trees the best we can by keeping them healthy and brace ourselves for the next invasive pest to show up on our shores.