I grew up with hedgerows full of dead elm trees and now we are faced with the prospect of hedgerows full of dead ash trees. A year ago, I wrote about the arrival of Emerald Ash Borer (EAB) in central Vermont. Since then EAB has been found in Groton, Stamford (near Bennington) and South Hero. It is time to talk practically about what individual landowners can and should do.
All landowners need to stay informed. Vermont has an excellent portal to all EAB information. Go to vtinvasives.org and you will find the latest map of the infestation along with information on all other invasive plants and insects in the state. This is also where you should report possible detections of EAB in your area.
When will EAB arrive on my land?
The EAB has been found just west of Spruce Mountain in Plainfield and also along Route 302 in Groton. In New Hampshire, EAB was detected in Concord six years ago and infested areas are now found from the Massachusetts line to Lake Winnipesaukee, including southeastern Grafton County. To the west, EAB was first discovered in western New York in 2009 and along the Hudson River south of Albany in 2010. Infestations now occur in 30 of New York’s 62 counties. EAB is well established in the Montreal area.
If they are not here already, the first EABs will alight in Peacham and Barnet within a few years and Danville and St Johnsbury a few years later. That timeline will change if EAB is discovered in other nearby towns. Go to vtinvasives.org to find the latest map of where EAB has been confirmed.
The insect may not be detected for three or four years after it arrives, while a population becomes established. By year five, the population will begin to grow exponentially, reaching a killing crescendo in another couple of years. By year 10, virtually all ash trees will be dead and the EAB population will crash and reach a low endemic level. Ash seedlings will continue to grow but will be killed as saplings by the endemic EAB population. With luck, we will be left with a few mature trees that are somehow resistant.
Life Cycle in Vermont
The adults feed on leaves and cause little damage. They lay eggs in crevices in the bark in mid to late summer. The larvae then bore inward to the phloem (inner bark where sap is carried from the leaves to other parts of the tree) and the outer sapwood where the tree is growing, adding a growth ring each year. They begin to feed on those tissues until the weather gets too cold. They feed in a serpentine pattern, leaving characteristic S-shaped galleries under the bark which get larger as the larva grows. A fully mature larva is about an inch long. After over-wintering, a mature larva pupates and develops into an adult as the weather warms. In Vermont’s climate, the adults begin emerging in June. They bore out through the bark, leaving a telltale D-shaped hole about an eighth of an inch across, and immediately fly to find leaves to eat and other adults to mate with. Then the adult lays about 200 eggs and starts the next cycle of life.
The infestation is not normally noticed until the tree is severely damaged. The early action is usually high in the crown of the tree. Dead branches appear, but many things can cause dead branches in a tree. Woodpeckers move in to drill for the EAB larvae and other delicacies. If an area of the trunk is already badly damaged by the insect, a woodpecker will use its beak to break off pieces of bark, revealing the EAB S-shaped galleries on the bare wood underneath.
It takes two or three years for the EAB to kill a tree. Everywhere it has been, this lovely insect has killed virtually all the ash trees. Only about one percent of ash trees appear to be surviving, presumably because of some resistance in that tree’s genetics. The best we can hope for is to slow the spread of the insect. We also need to leave some ash in the hope of perpetuating the species. Young, pole-sized trees are of little economic value but are producing seed that will germinate. They will still be fine for firewood after they die, so leave them to their fate. Ash seedlings will grow and some will survive long enough to produce seed themselves before the EAB kills them. Thus the gene pool will be perpetuated.
Ash trees dominate some hedgerows. From a wildlife perspective, hedgerows are edge habitat. The loss of ash trees could be an opportunity to enhance hedgerows. Evaluate the ash trees first in terms of hazard. Trees that will threaten nearby buildings or driveways should be taken down before they start dying because cutting dead trees is unpredictable and dangerous. There are numerous folks in Caledonia County who specialize in taking down trees safely.
Also, evaluate the trees for commercial value. Some hedgerow trees have sizable, straight trunks that contain valuable lumber. In a hedgerow, the lowest four or five feet must be left because of the likelihood of fence wire being embedded in the wood. But if the tree has a trunk with minimal or no branching that is at least eight feet long and 10 inches in diameter at the small end, you have a marketable log. To attract a logger to cut and buy these logs, you will probably have to join with your neighbors to get enough to make it worth the logger’s time. Of course, these trees also yield firewood. A forester should be engaged to work with you and your neighbors to evaluate the trees and work with a logger. Ash should be cut between October and April to avoid trucking wood from which adult EABs are emerging. If you’re not familiar with logging, 1,000 board feet, commonly written as MBF, represents the logs from three or four good ash trees. A standard log truck holds about 3,000 board feet, and a large truck could hold 5-6,000, so you and your neighbors will need to accumulate 12 to 20 decent trees to get a truckload.
Think about future hedgerow. Consider planting native trees and shrubs that will be beneficial to wildlife. For nuts, consider oak, beech, hazelnut, or chestnuts from the American Chestnut Foundation. Blueberry, nannyberry, cranberry, raspberry, blackberry, and elderberry are also good options. Apple, cherry, hawthorn, and dogwood all are beneficial.
Invasives will Flourish
Whether you cut ash in a hedgerow or in the woods, you will let a flood of sunshine hit the ground and seeds will germinate. Invasives will flourish, so be prepared. If you already have honeysuckle, barberry, buckthorn, or any of the other bad guys, consider control work before you cut the ash.
Controlling the Insect
In the 17 years of research since EAB arrived in Detroit, much has been learned but no effective control of the insect has emerged. Parasitic wasps, both native and imported, have been tested and show some promise in slowing the EAB killing wave. So far, the wasp population cannot grow fast enough to keep up with the EAB population as it builds in an area, but the wasp has promise as a long-term check on the residual EAB population. A fungus is being tested for its effects on EAB and early results are promising.
Chemical control is possible using systemic herbicides injected into individual trees. It costs $200-$300 per tree and the treatment has to be repeated every two or three years. There is no effective foliar treatment, so widespread chemical control is not possible. Treatment should only be considered for a particularly precious tree.
Work on developing resistant ash is the subject of a lot of research. Ash demonstrates a range of susceptibility to EAB with a few individuals lingering long after all the rest have died. Scientists are working on the genetics of Asian ash trees and hope to breed some combination that will be resistant. Genetic engineering could speed that process considerably.