While there have always been outbreaks of tree disease, about as many have appeared since the 1970s as in all prior recorded history. Globalization is the culprit. People and commercial goods now flow seamlessly around the globe, accompanied by a host of weeds, pests and pathogens. If you are a tree, death comes hidden in wood veneer, in packing material, shipping containers, nursery plants, cut flowers and imported saplings.
Today, EAB infestations have been detected in 30 states (and two provinces in Canada): Alabama, Arkansas, Colorado, Connecticut, Delaware, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Nebraska, New Hampshire, New Jersey,New York, North Carolina, Ohio, Oklahoma, Pennsylvania, Tennessee, Texas, Virginia, West Virginia, and Wisconsin.
Nationwide, the emerald ash borer has killed more than 100 million trees.
Estimated management costs, lost property values and lost revenues from timber exceed 1.6 billion dollars annually
This insect is generally considered to be the most important pest of the urban forest in the United States. During the past decade, much progress has been made in understanding basic elements of the biology of this pest and methods to control it, especially in the area of chemical control tactics.
Tracking the spread of EAB
It is generally believed that EAB arrived in North America near Detroit Michigan sometime prior to 2002 in wooden packing material or dunnage and escaped into the surrounding landscape where it established itself in ash trees. Since 2002, it has moved progressively outward in all directions, frequently abetted by humans as they move firewood, logs or other wooded products. A variety of studies conducted in the field estimate movement of EAB to range from less than 0.2 miles per year to more than 12 miles per year. Nevertheless, EAB can travel 60 miles per hour down the highway (in a moving vehicle) and show up where you least expect it. When Boulder, Colorado became infested in 2013, the nearest EAB find was 600 miles away in Kansas.
Resistant Plant Materials
To date, all known species of ash trees in America are susceptible to attack by EAB. However, in a recent study, Asian ash (Fraxinus mandshurica) experienced far less mortality than native ashes including F. pennsylvanica and F. americana. Four years of exposure to EAB resulted in more than 75% of North American ashes succumbing, but less than 20% of Asian ash died. Results of these studies demonstrate the existence of resistance in Fraxinus and provide arborists with hope that this tactic can be used to defeat EAB in urban ecosystems.
Also in the news, researchers have successfully decoded the entire genetic sequence of ash, an important first step in creating a genetically modified tree, resistant to the beetle.
The goal with biological control is to use natural enemies to bring EAB populations into balance and reduce damage; it is not a tool for eradication. In cooperation with several states, the USDA has reared and released three Asian species of natural born EAB killers; tiny wasps. The wasps hatch and feed only on EAB as they develop. The hope is that these wasps will decimate EAB especially in natural forest stands where few options for intervention exist. To date scientists have found released wasps living and reproducing, a hopeful sign they can provide another weapon in the fight against EAB.
Insecticidal Control of EAB
Chemical control can keep the beetle in check if applied regularly. Because the chemical is applied tree by tree, treating a forest with many thousands of ash is prohibitively expensive. But treatments can be affordable in areas where people want to preserve a few trees.
An excellent review of insecticides for controlling EAB can be found by clicking this link: EAB Insecticide Reviews.
In the treatment of ash trees, there seems to be much concern recently about the potential role of imidacloprid and related neonicotinoid insecticides in colony collapse disorder (CCD) in bees. Research is ongoing to investigate the relative effects of pesticides, bee pathogens and parasites, and nutrition on honey bee health.
Ash is wind-pollinated, not insect pollinated. Bees can and do collect pollen from wind pollinated species, and there are reports of honey bees collecting ash pollen. But to date there are no conclusive answers and researchers have not been able to establish a link between imidacloprid and CCD.
Conservation of honey bees is a critical issue and every effort should be made to protect honey bees. Ash trees provide important ecosystem services that can justify protection. The preponderance of evidence suggests that EAB treatments pose minimal risk to bees. Studies have also found that ash trees are most effectively treated for EAB just after the leaves emerge, which would be after they have completed blooming.
Ash and After
A 2009 study in the journal Biological Invasions listed 43 native insect species that rely on ash trees for food or breeding. Those insects are the food supply for birds, including woodpeckers. After the ash are gone, we end up with a different ecosystem, where some species thrive and where old ones don't do as well. It's important to note that a different ecosystem is not the same as no ecosystem. When the ash trees die, they are replaced by other kinds of trees.