Wednesday, August 11, 2010

Wilmington Tree Commission: The American Elm

1 in 100,000!  That is the estimated number of American Elm trees that is Dutch Elm Disease resistant, according to Michigan State University.

Wilmington is home to at least one of the survivors which escaped being subject to the disease that destroyed “77 million trees by 1970” according to Phil McCombs’ article in 2001 (Washington Post). One of our lovely specimen American Elm trees is located on David’s Drive at the Lytle Creek Greenway Trailhead Pavilion, across from the R+L Terminal.

Ulmus Americana, most commonly known as the American Elm tree (or White Elm, or Soft Elm), is native to North America and can survive temperatures as low as -44 degrees F.  Its vase shape grows quickly reaching a height of 80-100’ tall and 60-120’wide, with a trunk measuring a diameter up to 7’ at breast height.  It was once long-lived and able to reach 300+ years.

The American Elm on Davids Drive is over 2’ in diameter and stands over 55’ tall.

In the Spring before leafing-out, inconspicuous green flowers appear followed by seed-pods which feed birds and wildlife.  Elm trees are known for their great arching leafy limbs, which offer perfect a nesting habitat for the orange and black Baltimore Oriole. The leaves are alternate, about 3-5” long, and 1-3” wide, coarse with serrated margins, prominent veins, and have a downy under side. In Autumn, the leaves change from green to yellow before they drop.

The wood of the Elm tree was once used for furniture. Early settlers steamed the lumber into shape, particularly for rockers on rocking chairs, barrels and wheel hoops.

Dutch Elm Disease (Ceratocystis ulmi) is a fungus that grows in the sapwood of Elm trees and can spread underground from roots of nearby Elms by easily grafting together, as Elms have a shallow yet extensive root system.

Microscopic spores are also transmitted from diseased trees to healthy specimens by two kinds of beetles, (European bark beetle and the Native Bark Beetle), which tunnel under the gray-brown/flattened-ridged bark to breed and lay eggs. It is possible for 400-2000 beetles to emerge from a square foot of bark, according to Michigan State University Extension. Since the Elm Bark Beetle is attracted to freshly cut Elm, it is best to avoid pruning American Elms from April through August.

To detect Dutch Elm Disease look in the crowns for leaves with wilt in the summer, turning yellow, curling, and then becoming brown.

If you wish to try to treat an Elm tree to kill emerging adult beetles, insecticidal sprays such as Sevin or Dursban can be applied in early April when the beetles are active. The chemical is applied to the crown, bark and the tree base.

It is interesting to note that tree geneticist Dr. Alden Townsend has been plant cloning for 25 years and has introduced two new strains of American Elm trees which are resistant to Dutch Elm Disease. These are Ulmus americana "Valley Forge" and Ulmus americana "New Harmony.

If you are interested in planting an American Elm tree, which are perfect for our zone (Zones 3-9), it prefers full sun and are known to thrive in moist, rich soil.

The Wilmington Tree Commission encourages you to stop by the Lytle Creek Greenway Trailhead Pavilion and view one of Wilmington’s surviving American Elm trees. It was properly identified by Naturalist  Jim Ramsey, while Lori and Brandon Williams of the Lytle Creek League of Conservators assisted with the labeling of the tree. (View Photo of Marilyn Rollwage beside the American Elm Tree.)