Emerald Ash Borer: Time to Take Action By Thomas Badon, ASLA, Commercial Consulting Arborist, ISA Certified Arborist MN-4439A, Rainbow Treecare
Remember back in 2009 when the Emerald Ash Borer (EAB) was all the rage? All the major networks and newspapers were covering the topic. So what has happened to EAB? You hear a story once in a while, but with this extended winter it is certainly not getting the media attention it did back then. Does that mean the beetle is gone? Have the Twin Cities beaten this pest? That certainly would be wishful thinking; unfortunately, that is not the case. The reality is that the population is silently growing and in fact, based on the history of this pest, the population is currently increasing exponentially.
So What Can You Do?
There are several theories and opinions as to the best management practices, and several cities are beginning to develop plans of attack. However, removal seems to be the preferred method. If Michigan knew in 2002 what we know today, could they have saved some of the 60 million trees that were lost? Before we answer the question of “What can you do?” let’s look first at the basic facts about EAB.
Why Are There So Many Ash Trees?
Approximately one out of every five urban trees is an ash (Fraxinus sp.) tree, primarily of the Green ash (Fraxinus pennsylvanica) variety. It is not uncommon that more than 75% of many properties’ and communities’ urban canopy consists of ash trees. The ash tree planting craze started in the ’70s and early ’80s as a hardy alternative to the American elm (Ulmus americana). When the elm trees started to die from Dutch Elm Disease, everyone wanted a hardy, tough urban tree.
What is EAB and Where Did it Come From?
The Emerald Ash Borer (Agrilus planipennis) has killed millions of ash trees since its discovery in southeastern Michigan in 2002. Native to Asia, this insect was likely introduced to the United States in wood packing material carried in on cargo ships or airplanes. Through a combination of natural spread and human activity it is now found in Illinois, Indiana, Iowa, Kentucky, Maryland, Michigan, Minnesota, Missouri, Ohio, Pennsylvania, Virginia, West Virginia, and Wisconsin, placing millions of additional ash trees at risk.
Where Is it Around Here?
Managing emerald ash borer is enough of a challenge, just trying to save the trees from getting killed by beetles. However, in our roles as managers, consultants, and stewards of the urban forest we also need to be responsible for planning for the future. Back in 2002, when EAB was first discovered, Michigan had no idea what they were dealing with. As the insect spread quickly into surrounding states, Ohio knew what it was but did not know how to stop it. As the pest continues to spread, each state and community knows more and more about the pest. Unfortunately, places like Illinois waited too long to implement a proactive plan. The fact is, EAB is here and spreading throughout the Twin Cities.
How Does this Insect Kill ash Trees? The female Emerald Ash Borer lays its eggs on the bark of an ash tree and the larvae tunnel through the bark and begin consuming the sapwood of the tree. This feeding disrupts water flow to the canopy, dehydrating and killing that portion of the tree. Eventually, the whole tree will die. Unlike Japanese Beetles or Boxelder bugs, the Emerald Ash Borer insect is small and causes damage inside the tree, making it relatively hard to detect. Since this insect
often goes undetected for the first few years, the population grows very rapidly within the original tree, placing all the surrounding trees at high risk. Researchers at The Ohio State University have studied this “Curve of Death” since the original find and have discovered that it is possible that approximately 80% of the ash population can become infested and die within a fouryear time frame.
What Should I Look for?
First and most importantly, correctly identify that you are looking at an ash tree. Ash trees can most easily be identified by the shiny, dark green leaves that are compound (5-7 smaller leaves per leaf) and typically grow opposite of each other on a branch. Once you’ve identified your tree as an ash, begin to look for symptoms. Typically a tree will start dying from the top down, losing 30-50% of its canopy after two years of infestation. As the top of the tree continues to decline, epicormic shoots (new branches) begin to form near the base of the tree as the tree’s last hope to survive. If the tree is heavily infested, the bark will begin to sheer off revealing distinct “S” shaped galleries where the larvae have been feeding. The final tell-tale sign is “D” shaped exit holes about 1/8 inch wide created as the adults emerge from the tree. Due to the coarse nature of the bark, these can be difficult to spot at first glance. Typically by the time they are visible and near eye-level, the tree is already heavily infested.
Who Should I Listen to?
A Google search of Emerald Ash Borer yields more than 600,000 results. For as much quality information that is out there on EAB, there are more myths, confusions, half-truths, and misconceptions around this insect than maybe any other tree pest in history. To help combat some of this misinformation, the Coalition for Urban Ash Tree Conservation was formed. The Emerald Ash Borer continued on page 20 May | June 2013
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