By David L. Roberts, Ph.D.
The Emerald Ash Borer ranks with Dutch Elm Disease as one of the serious threats in its destructive potential to eliminate a genus of trees species, in this case Fraxinus, as a viable landscape and forest tree from the North American landscape. The story of the Emerald Ash Borer (EAB) (Agrilus planipennis) and its introduction and establishment into North America is both interesting and disconcerting. In brief, many scientists and government agents originally diagnosed the decline in southeast Michigan as ash yellows, a disease caused by a phytoplasma (bacteria-like microorganism) that tended to produce epicormic shoots on the tree trunk (similar to the EAB). Because of D-shaped emergence holes, the insect injury associated with declining ash trees was assumed to be the two-lined chestnut borer (TLCB) (Agrilus bilineatus), a native insect thought to be of secondary importance. I began a research project in June 2001 to study this ash decline even though no research funds were available, except from public donations. I was able to prove with DNA detection technology that ash yellows was not the cause of the epidemic decline of ash in southeast Michigan. Even though I was not an entomologist, I collected ash logs from a rather large geographical area with the intent of rearing out the adult of the insect thought to be the TLCB. No one in North America, including experts at Washington D.C.’s Smithsonian Institution, could identify the metallic green insect emerging from logs I had collected from an area of more than 2,000 square miles. Finally identified in Eastern Europe as Agrilus planipennis, which had no common name, we named the insect the Emerald Ash Borer.
As discoverer of the Emerald Ash Borer in North America, and as a plant pathologist and extension educator, I have probably worked on the Emerald Ash Borer longer than anyone else in North America. This article represents the first in a two-part series which reviews the successes and failures of Michigan’s attempt to address the EAB threat in North America. Hopefully, this information can be used to better confront this lethal pest as it advances to communities in other states and regions.
The EAB Containment and Eradication Plan
The approach to managing the EAB may be reviewed as originating on national and local levels. On a national level, various government agencies, scientists and the public had interest in eliminating the EAB from Michigan, its original site of introduction, which would also presumably eradicate the insect from North America. A “Containment and Eradication Plan,” part of which assumed the EAB could be killed by chipping ash trees to one-inch or less, was adopted by the Michigan Department of Agriculture (MDA) and the United States Department of Agriculture (USDA). This plan failed for several reasons. First, the science was questionable because insufficient, conclusive studies were pursued prior to implementation of the one-inch chipping policy. Also, investigative reporters discovered that ash trees were not being chipped to “one-inch” in ash marshalling yards in quarantined areas in southeast Michigan; this disclosure resulted in a quarantine language modification: a one-inch chip was redefined as measuring no more than one-inch on two sides.
Through survey work, I found supportive evidence that the EAB spread may have actually been hastened with chipping and transport of chips to areas of less quarantine regulation. My own ash grinding experiments in 2005 confirmed my suspicions, that the insect could survive the chipping procedures and that destroying ash trees will not necessarily stop the EAB. Decision makers in other states/locales should understand that costly and labor-intensive tree removal and chipping will not eradicate the EAB from their landscapes.
The EAB has become firmly entrenched and will likely be a permanent resident of North America. Realistically but regrettably, billions of ash trees are doomed in our forests and landscapes. There are, however, very reasonable approaches to save some ash trees for landscapes and for other uses such as seed reserves.
Short-term destructive analysis
On a local level, research was initiated in 2002 to evaluate chemical treatments for managing the EAB on individual trees to save them from the EAB-incited decline and death. Unfortunately, most of this government/university research was performed by scientists who largely depended on a destructive style research design. With destructive analysis, ash trees were treated with various insecticides and delivery methods, and subsequently analyzed by destructive means. Usually this involved two methods: cutting large patches out of trees to determine if EAB larvae survived the treatment; or cutting trees down and stripping the bark from trees to determine the number of surviving larvae. Both techniques result in the ash tree’s final demise even if treatments could have been efficacious.
There is no doubt that destructive analysis gathers quick data, however, we cannot discern from this research design whether any trees would have survived the treatments methods or various levels of insect control. It is likely that the scientists involved with this destructive research were hoping to find the one treatment that would yield 100 percent control of EAB larvae. It is very important to note that the EAB on ash is quite dissimilar to Dutch Elm Disease or Oak Wilt, where any contact with its fungal pathogen will usually result in lethal consequences for the host tree. In the case of the EAB, good health, decline or death of the tree is directly correlated to the number of EAB attacks on the tree. Few attacks may leave the tree largely unaffected; many EAB attacks can kill the tree. Unfortunately, the destructive analysis design was utilized by some scientists for several years, and, along with the chipping policy, probably delayed our understanding of how to manage the EAB effectively.
While certain scientists and government agencies were busy sorting out their agenda to manage the EAB on a national and local level, some of them were also dispelling the notion that trees could be saved from the EAB. News releases and government-sponsored videos seemed devoted to sway public perception by indicating that the “EAB is 100-percent fatal,” that “cutting and chipping was the only proven technique to kill the EAB” (untrue), and that any treatment to ash trees “would be expensive and would have to be done every year.” Some statements even went so far as to warn the public about arborists who sell EAB treatments. This bias probably resulted from the theory that if all ash trees in southeast Michigan were killed, then the EAB would run out of food and “burn itself out,” a theory extrapolated from containing forest fires.
Nevertheless, many arborists in southeast Michigan and I began our own treatments based on existing technology. We reasoned that even though the EAB was an introduced insect, it was nonetheless a coleopteran that should respond to many common insecticides registered and in use in the United States. In addition, as a scientist and educator at Michigan State University, I realized it was my responsibility — no, my obligation — to speak the truth and to present the public with all information and options available, effectively educating the public so that they may make informed decisions.
Mark Baldwin of Mark Baldwin and Associates, Inc. is one of the arborists who responded to the EAB threat quickly and with innovative techniques. In 2000, Baldwin had installed 30 ash trees in a gated community near Plymouth, Michigan, within a few miles of the location I believe to be the original release site of the EAB into North America. By 2001, trees were looking very poorly as evidenced by abundant insect injury to the trunk and limbs. On most trees, these “insect cankers” had girdled trunks by as much as 80 to 90 percent.
Because of this injury, Baldwin began treatments with insecticides in 2001, a year before I found the EAB; the trees were already responding very nicely to Baldwin’s treatments by the time I first observed them in 2002. I included his location and other arborist’s treatment sites into my research program for monitoring and further experimentation. The treatment protocol for this Plymouth site was Bayer’s Merit soil treatments and Arborsystems’ Wedgle Direct-Inject System using Pointer (imidacloprid) in 2001. In subsequent years, only Pointer was used. The treatments provided 100-percent control of the EAB. Not only did all 30 ash trees survive and recover, but no new injury or attacks were found based on canopy, trunk and limb injury ratings since 2003. These trees have recovered to such an extent that for the past several years they have been putting on a minimum of two to three feet of growth per year.
In 2005, I initiated a study at this Plymouth site in which 10 trees each would receive the following treatments: 1) Pointer ever year, 2) Pointer every two years, and 3) Pointer every three years. The objective of this study was to determine whether multiple-year control could be achieved from one treatment after the frontal EAB epidemic wave had passed through an area and decimated most trees; all non-treated trees for miles around this Plymouth site had long since died and had been removed (or so we thought). In 2007, the experiment was stopped because we discovered an infested homeowner tree only 30 feet from our experimental trees. This infested tree, “half dead” due to intermittent treatment with Merit, hosted dozens of newly emerged swarming adults, which threatened some of our experimental trees that had not received treatment in three years. Because the “Typhoid Mary tree” was removed during the winter of 2008, we restarted the experiment with the same protocol. Even so, we found through chemical residue analysis and visual ratings that we had obtained 100 percent control of the EAB with treatments only every two years, even in the presence of significant “insect pressure.” In some cases, residues of Pointer measured well over 1,000 parts per billion, many times more than enough insecticide to yield excellent control of the EAB. It’s possible that we might have achieved three-year control from one treatment had we not stopped the experiment. Because of the wildly successful results and because I know of no other treatment study of this duration, I labeled this Plymouth site “the world’s longest running and most successful EAB field control demonstration.”
In part two of this article in the July issue of Arbor Age, I will provide evidence of much larger sites with larger trees, discuss the new emamectin benzoate material, to be sold as Tree-äge by Arborjet, Inc., and detail some guidance on what treatment protocols are most efficacious.
David L. Roberts, Ph.D., is a plant pathologist and academic extension specialist at Michigan State University (MSU). For more than 14 years, Dr. Roberts was director of MSU’s Plant and Pest Diagnostic Clinic. During the past 25 years, his research and extension activities have focused on Oak Wilt, Dutch Elm Disease and Beech Bark Disease, as well as many other issues. In 2002, his research led to the discovery of the Emerald Ash Borer.
A video of some of this information can be viewed at treeresearch.org. For a free copy of the video, please contact the author at firstname.lastname@example.org.
Author’s note: Neither the author nor Michigan State University endorses any particular product. When using chemical treatments, be sure to follow label directions and comply with all regulations in your state.