What’s Killing the Ash Trees?  

     The title of this article seems like a ridiculous question, but is, nevertheless, a very pertinent one. Obviously, most people assume the Emerald Ash Borer (EAB) is killing all the ash trees in Southeast Michigan. However, long before the EAB arrived on our shores, ash trees were infected and infested by a barrage of diseases and insects, respectively. Anthracnose, a very common fungal disease during this year and past years, causes ash trees to develop leaf blotches; trees infected with the anthracnose fungus may defoliate during the summer months. I know of many arborists who received complaints from their clients who mistakenly believed this defoliation was due to EAB; homeowners subsequently complained that the EAB treatments were not working. Anthracnose is not lethal but may provide additional stress to trees, predisposing them to many other problems including the EAB. There are lethal diseases as well. Verticillium (fungus) is well known to cause lethal wilt on a variety of landscape plants and is also lethal on ash. The complicating factor with Verticillium on some species of ash is that there are no visible internal signs of vascular discoloration that many of us are programmed to recognize during diagnostic examination. On some species of ash, Verticillium may only be detected by lab culture. There are a variety of other insect/borers that infest ash trees. Some are lethal; some are not. Some are secondary opportunists.

Association of Canker Diseases with the EAB:

     In 2002, shortly after my research led to the discovery of the EAB, I began to notice that some trees were developing cankers in areas wounded by the EAB (Photo 1).  It may only take one wound, either from improper pruning, storm injury or the EAB to introduce a fungus that is capable of killing an ash tree. Obviously, with 100’s to 1000’s of wounds from the EAB on a single ash tree, the chances of introducing a lethal disease increase. The best science may demonstrate that the EAB can be controlled with insecticides, but we may still lose the tree from diseases. Recognizing these issues can be very important in our overall management of the EAB and ash problems. These canker diseases, potentially caused by many different types of fungi, may be considered primary or secondary. Primary diseases are ones which of their own accord can cause the decline and death of trees. Secondary diseases usually require encouragement or predisposition from a variety of factors, such as drought stress and poor planting/site situations and other diseases such as anthracnose. These factors need to be considered when an arborists, and even scientists, attempt to save ash trees by insecticide treatments.

 

Exotic Pests & Exotic Pathogens:

     Today, with the global economy, the chances of introducing new pests and new diseases that are considered exotic and hence devastating to our environment are increasing. What is particularly difficult if not downright ironic is that we cannot predict what will be devastating. The EAB was not a well-researched insect in China primarily because it wasn’t considered much of a serious pest there. In the case of the beech bark disease, both an exotic insect, the beech bark scale, and exotic lethal fungi, Nectria species, were introduced and have the potential to devastate our native beech trees. One of the main problems with the EAB program is that there appears to be no research on axillary issues such as diseases, cultural factors, etc.  In early 2003, I submitted a proposal to look for exotic fungi that may have been introduced with the EAB, like beech bark disease; the proposal was rejected, presumably due to the overwhelming focus on the insect, while ignoring other possible important aspects. Finding and identifying an exotic fungus will be far more difficult than finding and identifying the EAB. This rejected grant proposal also contained work to examine interactions of the EAB with various diseases such fungal cankers. Regrettably, certain individuals within MDA and MSU are not interested in what I believe could be a very important research effort.

 

Insecticide Treatments and the Dilemma of Declining Ash Trees:

     Many arborists have been perplexed about the variable results they obtain with their insecticides. Treatments seem to work very well some of the time, but other times, the trees continue to decline. I have examined a number of trees that have been treated with insecticides. For example, a large tree (Photo 2) in Grosse Pointe Farms continued to decline despite the fact that Shock Brothers threw everything in the insecticide arsenal at the tree. It was decided to severely “top” the tree to determine if shoots emerging from the lower branches might somehow allow the tree to survive. In dissecting the upper branches with Sue Shock and company, we could not find one live insect, even in healthy succulent green cambial tissues. The lack of viable insects in this tree suggests that the insecticides were very effective but that the continuing decline may be the result of factors other than insects…. possibly diseases.

 

Can Teamwork Solve the Ash Problem?

     Virtually all universities and government agencies will profess to support teamwork. But is it really teamwork if capable scientists, tree care professionals, educators and even the public are prevented from expressing their views and/or working on the team? As an example, a rather large study of transplant-sized trees was installed at the Tollgate Center in Novi, Michigan (Photo 3). This study was designed to examine the susceptibility of various ash species/varieties and other genera of trees to the EAB and to local Southeast Michigan environmental conditions. Unfortunately, even though this study is within a couple hundred yards of my office, I have not been asked to be part of the team to examine these trees for other problems. It may be very short sighted to assume that all of the ash trees in this study as well as other ashes around Michigan will be affected exclusively by the EAB. Many of these trees at the Tollgate site have fungal cankers developing on their stems and branches (Photo 4), but under the current management, it will be unlikely that we will ever know what role these cankers and other factors have in the decline and death of these trees. Furthermore, because such extensive effort was devoted to establishing this experiment, wouldn’t it be interesting to know which species/varieties are susceptible to diseases? While a particular variety of ash may show tolerance from EAB attacks, it may not be the best landscape tree if it defoliates by June every year because of its susceptibility to anthracnose.

      Regrettably, I believe that the current “teamwork” on the EAB project is selective and exclusive. We may not know for quite some time whether an exotic disease has been introduced with the EAB or if native diseases are interacting with the EAB to increase mortality on our ashes. We are already more than two years behind schedule in examining these possibilities. We need to foster debate, discussion and diversity in approaches to resolve the EAB crisis. Otherwise the public, the industry and the environment will suffer the consequences.  

  

Photo 1 - Canker wounds	Photo 2 -  Removal of declining ash after treatment	Photo 3 - Rows of ash trees planted for research in SE Mich. found 1/3 dying within a year.
	Photo 4 -  Fungal canker on trunk & branches

EAB Site Navigation:
  EAB Homepage
  Photo Gallery I - EAB
  Photo Gallery II - EAB & Ash Trees in Decline
   Ash Tree Decline Research History & Management
  Identification of Stages of EAB Decline & Whether Treatment is Necessary
  Links
  EAB: Winter Management Through Sanitation
   How well do Insecticides work for EAB?