By David L. Roberts, Ph.D.
The prognosis for the Emerald Ash Borer (Agrilus planipennis) is that this invasive pest increases in population at least ten fold every year and will advance across North America in a huge ash-killing wave front. While the advancing wave front of billions of insects is largely invisible to humans, the path of destruction of declining and dead ash trees will be quite evident. Failure to detect the insect early in its release into North America and the subsequent failure of the cut and chip program have ensured that the EAB cannot be eradicated from North America. The exceptions to death will be those ash trees that receive treatment. Unfortunately, at this time, chemical pesticides are the only treatment that can provide the best hope for managing the EAB on individual trees.
There are occasional press releases from scientists who infer promises that collection of parasites, predators and pathogens of the EAB in China and their release into North America will help to manage the EAB. What is not usually related is that the reason EAB is not a particular serious pest in Asia is because ash trees (Fraxinus sp.) in Asia are tolerant — if not resistant — to the EAB, a product of thousands of years of evolution and balanced coexistence. It is doubtful that release of these biological controls into North America will preclude the need for treatment, if specific ash trees are to be saved.
There are a variety of treatment options currently available that may provide effective control of EAB. These include several different types of delivery methods and various chemicals as follows:
One or two well-timed trunk and branch sprays in June and July have given reasonable control, sometimes more than 90 percent according to some tests. The insecticides are applied as cover sprays to the trunk and canopy, providing protection from the EAB. Some of the chemicals that have been tested include Onyx, Orthene, Tempo and Sevin. Onyx seems to be a particularly effective treatment.
Typically applied as imidacloprid in water, the solution is drenched around the trunk region where fibrous roots will absorb and translocate the chemical through the trunk to the upper branches. Bayer’s Merit has been the predominant trade name, but other formulations/trade names are also now available.
Using this method, chemicals are injected into the base of the trunk where the insecticide is translocated through the trunk and into the branches, twigs and foliage. The three established EAB injection delivery systems currently on the market those offered by Arborjet, Arborsystems, Mauget and Rainbow Treecare Scientific Advancements. Acecap tree implants is another modification of trunk injections. Other systems are being/have been developed, and some are available. Also, there are some “trunk penetrants” on the market, but I am not aware of their effectiveness.
It is important to convey that, respective of scientific studies and field observations, all of these delivery systems have provided reasonable, effective control of the EAB (see Photo 1) and all have also failed. In my experience, the reason for failure is most often due to treatment applications after the EAB has already colonized ash trees. One example of a failure in control, which approximates the dilemma faced by many arborists, is illustrated by a 24-inch diameter trunk section provided to me by an Arborjet technical representative (see Photo 2). This tree was injected with Arborjet’s Ima-jet, which, according to some university studies, can provide 100 percent control of the EAB. In this example, highly effective control occurred in one-inch bands above the Arborjet injection sites, but all of the vascular tissue between the injection sites succumbed to the EAB larval feeding, resulting in death of the tree. The wide spacing of the injection sites may have also complicated this management attempt. If this tree had been treated several years earlier, before the EAB attack, this tree would undoubtedly be alive today. All types of treatments are prone to failure if insecticides are applied too late in the EAB infestation/life cycle on specific trees. Also, some EAB treatment procedures proclaim that their treatments will provide at least two years of control. Given the above failure scenario (Photo 2), we must be very cautious about believing we can achieve two-year control if ash trees haven’t been treated for several years prior to the EAB’s arrival in your locale.
Late treatment, after the EAB has infested trees, is perhaps the greatest challenge facing arborists and individuals who want to manage the EAB on their ash trees. This challenge results from several factors, but can be attributed much of the time to the insidious/secretive nature of the EAB, whose presence is usually very difficult to detect in an area. Also, there has been a strong tendency in Michigan for many individuals to procrastinate on treatments for their ash trees until decline becomes evident. In the advancing EAB wave front, a very healthy ash tree can decline to beyond salvage in one season.
There have been some exceptions to late treatments; for example, trees at “the world’s most successful treatment site,” as discussed in part one of this feature, were literally brought back from death. Tree trunks at this site were literally 80 to 90 percent girdled in 2002. In addition to the treatments, their complete recovery was probably due in part to their young age and vigorous, aggressive growth along with fertilization and irrigation inputs. But, as they say, don’t try this at home; the take-home message is to get treatments on desirable ash trees early, before the EAB arrives. Otherwise, as Dirty Harry might say, “Do you feel lucky?”
Syngenta Crop Protection, Inc. and Arborjet, Inc. have cooperatively developed emamectin benzoate to be sold as Tree-äge. Michigan Department of Agriculture (MDA) spokesperson likened Tree-äge to a “silver bullet” for EAB management. Another MDA administrator was quoted as saying, “Though this is not a silver bullet for eradicating EAB across the country, it could be a quantum leap forward in our ability to slow the spread of this deadly insect.” Both of these statements may be misleading to the public. First, Tree-äge is not a “one shot deal,” sending the EAB packing back to China; repeat treatments will be necessary. And, like all the other effective options available, Tree-äge cannot slow the spread of the EAB across North America unless millions of tree owners begin treating their trees. Also, Tree-äge, particularly as a two year treatment, is not likely to alter this potential for failure if treatments are applied after the EAB has attacked ash trees. Perhaps the greatest contribution Tree-äge has made thus far is to inform the public that ash trees can be saved through treatment a notion countering some previous government/university press releases. Can Tree-äge improve on the 100-percent control we’ve already achieved by various treatment methods? Not likely. Regardless, Tree-äge has potential to be another terrific tool in our arsenal to combat the EAB.
Based on our front-line experience with the EAB in Michigan, the following can be offered as tips for managing the EAB as the insect advances into your area.
1) EAB advancement: Track the EAB’s progress into your state, county and locality. As much as possible, be on top of the progress of the EAB into your area of responsibility.
2) Assess tree health: Spring, after tree leaf-out, is the best time to assess tree health because the canopy density and health is directly correlated to cambial tissue integrity. Tree appearance later in the season may not reflect the true health of the functionality and integrity of cambial tissues after several months of EAB larval feeding. Learn to recognize symptoms of EAB infestations on ash trees to help early detection in your area. Possibly the earliest evidence is woodpecker activity on EAB infested trees. Branch decline, the presence of D-shaped emergence holes and leaf drop are rather advanced symptoms of EAB, which may make successful treatments difficult. Also, we must be able to differentiate EAB decline from other problems such as Verticillium wilt and anthracnose, which may cause leaf drop and be confused with EAB decline. For information on symptoms and detection, visit www.anr.msu.edu/robertsd<ITAL]
3) Educate your clients: Arborists can take out advertisements in local publications and perform “public service” TV interviews to inform the public about the EAB threat. Ideally, treatments should begin two to three years before the EAB “population front” arrives. This part can be tricky, because homeowners are sometime suspicious of arborists who try to proactively sell treatments, particularly after some government-sponsored releases previously called into question the integrity of arborists who sell EAB treatments.
4) Promote trees: The positive attributes of trees, and of ash trees in particular, are poorly understood by large segments of the public — particularly compared to investments in lawns. A large ash tree in someone’s front yard is quite valuable and may, for example, pay for EAB treatments in yearly savings for air conditioning costs. Furthermore, removal of a large ash tree and the planting of a small substitute tree is quite costly and will probably not yield large tree benefits during your clients’ lifetime. It may be prudent, as research is showing, to stress that after the EAB population front passes through an area, treatments of ash may be reduced to every other year or perhaps every three years; this can make the marketing of treatments more palatable over the long term.
5) Consider treatment options: It may be wise to discuss the various treatment options with your clientele. For example, if treating before the EAB arrives in an area and to avoid injury to trees from drilling wounds associated with some injection procedures, use of soil drenches to achieve uptake and distribution of imidacloprid may be advisable. Environmental factors could also be evaluated for personalized treatment; whole-tree sprays and soil drenches may be less environmentally friendly than trunk injections, which tend to isolate the chemical within the tree. Yet another factor, some people may want to avoid drilling trees for some injection procedures and use non-drilling trunk injection procedures or soil drenches or spray treatments.
6) All is not lost: Even if treatments are made after infestations of a particular ash tree, sometimes ash trees can still be saved. Some of the examples I provided in Part I and below are examples in which ash trees have been saved after the EAB was detected in a locality — largely because my discovery in 2002 was made after the EAB was already established over several thousand square miles in Michigan. In particular situations, where EAB infestations already occurred, I have recommended two or even three delivery methods every year for several years to stabilize specific ash trees.
More successful treatments
In part one of this feature, I presented the case of the treatment site near Plymouth, Michigan, not far from the original release and epicenter of the EAB into North America. Because there has been so much negative press about saving ash trees from the EAB and because many individuals may still be skeptical of the effectiveness of EAB treatments, several more examples of highly successful treatments are as follows:
Gross Point Farms, Michigan
Sue Shock, president of Shock Brothers Tree Care is passionate about trees and life. Among many accounts, her company maintains under contract the trees of the City of Gross Point Farms. The “City of Trees” is thoroughly committed to tree health, and residents view their trees as a valuable resource. With cooperation from city officials, Sue began treating ash trees as soon as my research uncovered the EAB in 2002. Even with this very early response, many of the trees were already infested with EAB. Of 600+ trees under treatment (Photo 3), Shock has lost only one tree to the EAB in the past six years. Incidentally, Gross Point Farms is also home to a large population of American Elms, due to an aggressive treatment and sanitation program. It is one of the few places in the Midwest where traveling down a city street, one is still greeted by the graceful, cathedral-like arches created by large, mature American elms.
Oakland County International Airport, Michigan
Wayne White started a business (Emerald Tree Care, Inc.) devoted almost exclusively to EAB management. He was so confident in his treatment protocol that he offered a guarantee. Photo 4 shows his successful treatment of white and green ash at the Oakland County International Airport, just one of numerous locations managed by White. As with other successful treatment examples, untreated trees in areas directly adjacent to the Oakland County International Airport died several years ago (Photo 5). White has also expanded his business into other states and initiated a referral service with other businesses.
Photo 4 Photo 5
This article does not do justice to all of the arborists in Southeast Michigan, who began treating ash trees and implementing innovative techniques long before any scientific research was completed. And I must submit that some of the scientific research has been variable, somewhat conflicting, and even questionable at times. Even so, we now know that we can save ash trees from the EAB. Even more remarkable, I believe the EAB is more easily controlled than some of our common landscape problems, such as Zimmerman Pine Moth and Diplodia Tip Blight on Austrian Pine, Dutch Elm Disease, Phytophthora Bleeding Cankers and Collar Rots and Pine Root Collar Weevil.
David 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 www.treeresearch.org
For a free copy of the video, please contact the author at email@example.com
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.