Rough times for this beautiful tree
by Steve Carroll, Contributing Columnist
A mature, open-grown white ash is a magnificent tree. It grows straight and true, with bark ridges that interlace to form elongated diamonds. It showcases leaves with multiple leaflets that emerge in pairs along branches. After fertilization, flowers develop into clusters of dry, winged, one-seeded fruits. In the fall, leaves turn from yellow to purple. If not for one problem, ash would be a great choice for that open space in your yard, or along an avenue in need of shade.
The problem? The emerald ash borer, an introduced beetle that is spreading rapidly and leaving millions of dead ashes in its wake.
THE ASH TREE
Ashes (genus Fraxinus) are in the olive family, closely related to the family’s namesake and to our native fringe tree (Chionanthus virginicus). Our regions two most common ashes are white ash (Fraxinus americana) and green ash (Fraxinus pennsylvanica).
White ash can reach 2 to 3 feet in diameter and 80 or more feet tall. Its compound leaves typically have seven smooth-edged or faintly toothed leaflets. Male and female flowers form in clusters, usually on separate trees.
Green ash is similar, sometimes reaching more than 100 feet tall. The two may grow together, though white ash prefers moist, well-drained sites while green ash better tolerates damp or even temporarily flooded sites.
According to the Virginia Department of Forestry, the half-inch long emerald ash borer is “the most destructive forest insect ever to invade the United States.”
Homeowners can spot the tiny, iridescent green adults after they emerge through D-shaped exit holes in the bark. The adults may chew ash leaves, but the larvae do the real damage, inevitably leading to the tree’s death.
After adults lay eggs in the cracks of bark, the larvae feed and burrow through sinuous cavities, called galleries, in the tree’s conducting tissue. This disrupts the flow of water and nutrients, resulting in the death of branches in the canopy. Eventually, the tree is girdled and sometimes dies in as few as two to three years. Once significant damage is seen in the canopy, it’s generally too late to save the tree.
WHAT TO DO
Homeowners who have ash trees on their property should be vigilant. Examine the bark for the D-shaped exit holes; adults emerge in the spring, about the time black locust trees are flowering. You can also scan the canopy for signs of damage and die-back, and watch for increased feeding by woodpeckers, which seek out the larvae.
If caught early, or as a preventive measure, systemic chemicals can be used against this pest, but check first with a certified arborist or state forester. Also, keep in mind that chemicals used against the emerald ash borer may end up in birds and other organisms that feed on them. To protect pollinators, it’s best to treat trees after flowering.
Another promising treatment involves the release of tiny parasitoid wasps. These wasps lay their eggs in either the eggs or larvae. When the wasp larvae emerge, they feed on and kill the ash borer.
If you have healthy ash trees, contact the Department of Forestry at dof.virginia.gov to inquire about cost-sharing programs available to landowners and organizations. In the meantime, don’t transport ash firewood, chips or logs to avoid moving this pest into new areas.
WHAT WE’VE LOST
As with the American chestnut, a once grand and important part of our forest has been decimated. Though efforts are underway to combat this invader, it’s too late for many millions of trees.
Ash historically had many uses as baseball bats, tool handles, in early tennis rackets and pole vault poles, in furniture and interior finish, and as a food source for birds and other wildlife. Ash was also widely planted as a shade tree along urban and suburban streets.
Sadly, we should avoid planting ash trees on our properties until treatment is better assured. Fortunately, many other beautiful native trees do well in our region.
Steve Carroll is a botanist and ecologist who speaks and writes about trees, gardening and the world of plants. He is the co-author of “Ecology for Gardeners,” published by Timber Press.