Emerald ash borer — a risk to ash trees locally and across North America

In an attempt to raise awareness and increase knowledge about an extremely destructive, invasive insect pest known as the emerald ash borer, New York marked its 4th annual Emerald Ash Borer Awareness Week earlier this month. New York has more than 900 million ash trees, representing about seven or eight percent of the trees in the state. All are at risk.

The economic and environmental impacts of emerald ash borer infestations have been devastating and State leaders are asking forest landowners, campers, hikers, and other outdoor recreation enthusiasts to keep a watchful eye out for EAB and to report possible infestations. New York state’s forests and parks are high-risk areas due to firewood movement and New Yorkers are instructed to use only locally-sourced firewood when burning it at home and, when travelling, to buy firewood where you will be burning it and make sure you burn it all. Don’t take it with you. Emerald ash borers are not very aggressive flyers and on their own they do not move very far. Hiding in firewood, however, the insect may be transported over great distances. In fact, the rapid spread of the insect is believed to be primarily the result of people moving it from one place to another in firewood and other wood products.

Background Information

The Emerald Ash Borer is a native of northeastern China, North and South Korea, Japan and Taiwan. It is believed to have made its way to the United States in wooden shipping crates.

It was first discovered in the US in 2002, near Detroit, Michigan. During that same year, it was also found across the Detroit River in Windsor, Ontario, Canada. However, a new research study, which looked at tree rings in core samples from more than 1,000 ash trees killed by EAB across six counties in southeast Michigan, found that ash trees within the 5,800 square mile area being studied were being killed by EAB beginning as early as 1997. Since it takes many years for EAB beetle populations to become large enough to kill ash trees, the team concluded that EAB has been in southeast Michigan since 1992 or 1993; and perhaps even longer. The study was conducted at Michigan State University and the results of the study are published in the current issue of the bio-geography journal Diversity and Distributions.

The beetle has been rapidly expanding its range ever since. It is now responsible for the destruction of more than 40 million ash trees in southeastern Michigan alone, with hundreds of millions more lost in 22 states (Michigan, New York, Ohio, Indiana, Illinois, Maryland, Pennsylvania, West Virginia, Virginia, Wisconsin, Missouri, Minnesota, Kentucky, New Hampshire, Massachusetts, Connecticut, North Carolina, Georgia, Tennessee, Iowa, Kansas and Colorado) and two Canadian provinces (Quebec and Ontario). Presence of EAB was also confirmed in Somerset County, New Jersey, just last week.

Signs and Symptoms

New York State has been actively surveying for EAB since 2003, inspecting declining ash trees, looking for signs and symptoms of EAB activity, and setting traps throughout the state.

Symptoms of EAB infestation include:

  • Dieback of the upper and outer crown
  • Epicormic (from dormant buds which lie beneath the bark) sprouting at the base and/or on the main stem of the tree
  • Vertical splits in the bark
  • Woodpeckers activity

It is important to note, however, that these symptoms do not confirm the presence of emerald ash borer.

Signs of emerald ash borer do confirm the presence of emerald ash borer – Signs of emerald ash borer infestation include:

  • D-shaped emergence holes
  • Serpentine larval galleries created as the larvae feed on the sapwood, which interrupt the movement of water and nutrients, eventually killing the tree
  • Creamy white, comparatively flattened larvae made up of ten somewhat bell-shaped segments (EAB larvae grow through four stages of development, eventually reaching a size of up to one and one half inches in length.)
  • 3/8 to 1/2 inch long adults with metallic green wing covers and a coppery red or purple abdomen. Adult EAB may be seen feed on ash tree leaves, but their feeding does not cause very much damage.

Emerald ash borer

in New York state

Emerald ash borer was first discovered in New York State in mid-June of 2009, in the Cattaraugus County town of Randolph. The infestation was reported to the state Department of Agriculture and Markets by Rick Hoebeke, a Cornell University entomologist (who is also assistant curator of the university’s insect collection; the world’s largest at seven million specimens), after two United States Department of Agricultural (USDA) research service employees recognized damage to ash trees just off of Interstate 86, at Exit 16. In an effort to limit the potential introduction of EAB to other areas of the state, the state Department of Environmental Conservation established a quarantine in Cattaraugus and Chautauqua counties, which restricted the movement of ash trees, ash products, and firewood from all wood species.

In June 2010, DEC announced that several more trees in Randolph had been found to be infested with EAB. DEC foresters responded by cutting and chipping nearly 100 ash trees from both public and privately owned woodland; all within 2 miles of the original confirmed sighting.

In 2010, emerald ash borer infestations were also confirmed in Monroe, Genesee, Livingston, Steuben, Greene, and at 13 separate locations in Ulster County. Confirmation in Livingston, Steuben and Genesee Counties came when adult beetles were found in purple USDA Animal and Plant Health Inspection Service EAB traps, which had been hung in those counties by DEC forest technicians. As a result of those findings, DEC added 16 more counties to existing state quarantines and the quarantined zone grew to include almost all of western New York, as well as Greene and Ulster Counties in the Catskills region.

A quarantine now exists in all or part of 42 New York counties. It spans the state from east to west and is comprised of pretty much every county south of the Adirondacks, excluding only those that are generally considered to be the greater New York City metropolitan area.

Emerald ash borer infests and kills all North American ash species. Most trees die within 2 to 4 years of becoming infested. Emerald ash borer does not infest mountain ash, a popular landscape tree. Mountain ash is not a true ash. It is actually part of the Rose family.

EAB life cycle

There are exceptions, but most emerald ash borer beetles have a one-year life cycle. Adult emergence starts in late May and peaks in June. However, some adults emerge later and emergence of small numbers of beetles may continue throughout the summer.

Adult females lay eggs from the middle of June well into August. Female EAB deposit their eggs individually on ash trees, between layers of outer bark and in cracks and crevices of the trunk and major branches. The eggs hatch in about two weeks, depending on temperature. Newly hatched larvae tunnel through the bark to the cambial region and feed on phloem. Phloem is a thin layer of tissue beneath the outer bark that moves sugars and other nutrients through the tree.

Most of the larvae will mature in September. These fourth-instar larvae; often referred to as pre-pupae and sometimes called “J”-larvae, spend the winter inside small pupation cells constructed in the outer sapwood.

Once the winter has passed, the overwintering, mature larvae will pupate inside their pupation cells, gradually transforming into adults. Pupation usually takes 2-3 weeks.

Less mature larvae spend the winter in feeding galleries in the phloem and outer sapwood. These less mature beetles may continue to develop and feed for yet another summer before reaching the adult stage.

Forest management options

While most forest landowners in this region need not change their scheduled timber management activities, they may wish to consider maintaining ash at no more than five to 10 trees per acre or at the minimum basal area allowable by their forest management plan, when conducting regularly scheduled timber harvest activities. A lower ash density will reduce the economic impact, should emerald ash borer reach a stand. Lower ash density may also slow the spread of the insect.

Forest landowners should stay informed about where EAB has been found. Properties that are closest to confirmed infestations are at the greatest risk for mortality, in which case it may be appropriate to accelerate a planned harvest, which also serves to reduce the amount of food or host material available. Guidelines based on the development of an infestation will be formulated by DEC and the United States Forest Service.

In the event that the emerald ash borer cannot be contained, the USDA Natural Resources Conservation Service is taking steps to see that the ash tree does not vanish forever. The NRCS Rose Lake Plant Materials Center in East Lansing, Michigan has an agreement with the National Center for Genetic Resources Preservation in Fort Collins, Colorado for storing ash tree seed as part of the National Ash Tree Seed Collection Initiative. Should ash tree populations become completely decimated by EAB, the stored seeds can then be used as the genetic base for re-establishing ash trees for future generations.

Landowners are being asked to watch for signs of infestation in their ash trees. If you believe that you have seen EAB, it is important that you report it by contacting me at Extension, or by calling New York State DEC’s Forest Health Unit at 518-402-9425.