Montshire Minute: Dutch Elm Disease

Originally aired during the week of September 7, 1998

Monday

Drive through any small New England town and you see the same street names. Like Maple Street. Chestnut Street. And Elm Street. Heck, every town has an Elm Street. Problem is, there aren't many elm trees there any more. Old photos of Vermont and New Hampshire villages show streets lined with stately elms, noted for their graceful, vase-shaped canopies that provided shade and a certain grandeur to the townscape. In the forests, the elm also dominated its surroundings. Tom Wessells, in his book Reading the Forested Landscape, tells us that the elms growing in floodplain forests and along riverbanks often towered over 100 feet high. But Dutch Elm Disease, caused by a fungus carried by elm bark beetles, has wiped out most elm trees across the country. Some old elms survive today, but more succumb each year.

Tuesday

When European immigrants settled the New World, they brought lots of baggage with them. Among other things, they carried the chicken pox, against which Native American tribes had no immunity. Plants and animals can also be affected by imported epidemics. Take Dutch Elm Disease, for instance. In the early 1900's the elm bark beetle, a stowaway in a lumber shipment from the Netherlands, arrived in Massachusetts without a passport. Elm trees seemed particularly appetizing to the elm bark beetle. They fed on elm trees, and bred in elm trees. But the real danger to the elm was a fungus the beetle carried with it. The fungus breaks down the elm tree's vascular system, stopping water and nutrients from reaching the leaves. The leaves then wilt, turn yellow or brown, and fall. The fungus, carried by the elm bark beetle, can also spread to nearby trees through the roots.

Wednesday

Dutch elm disease really did a number on American elms during the 1940s and 1950s. Now some younger trees of that era are now showing signs of the disease as they mature. An infected elm tree may show a yellowing of leaves in the crown. Leaves may start dropping from one branch, than another. Diseased trees may also leaf out in the spring with smaller leaves, indicating a late fall infection from the previous year. The entire tree may wilt and die over the course of a few months or years. Experts say that if a tree has symptoms of Dutch elm disease it should be cut immediately. Then, the trunk and branches need to be destroyed to prevent elm bark beetles from feeding off the dead wood. Elm bark beetles can move from one tree to another through the root system. Breaking root connections between diseased and healthy trees can prevent the fungus from spreading.

Thursday

If you've got an elm tree on your hands that may be suffering from Dutch Elm Disease, what can you do? Like fighting a cancer in the human body, prevention and early detection are the best bets. If the tree is showing early signs of the disease, pruning infected branches well below the outbreak can help. But if the fungus in the main stem of the tree or if the roots are infected, pruning is too little, too late. Fungicides injected into the roots of elms already inoculated by bark beetles may save some trees in the early stages of the disease. But these injections are expensive and need to be repeated every few years. Some researches hope that elms that have survived Dutch Elm Disease may naturally build up resistance to the fungus. Agencies like Elm Research Institute are busy developing a strain called the Liberty Elm they hope will be resistant to Dutch Elm disease.

Friday

Elms are not the only native trees that have been bedeviled by blight. An Asian fungus destroyed almost every American chestnut tree in the first half of this century. And beech trees have been affected by beech bark disease, caused by another non-native pest. Beech scale insects which are thought to have arrived from Europe around 1890 pierce the bark of the beech tree to feed on nutrients inside. These wounds allow a fungus to gain a foothold, eventually killing the bark and the tree. Only about 1 percent of American beech trees seem to be able to resist infestation. The first signs of the disease in Vermont appeared in Proctor in 1949, and Vermont has received several infestations since then. Loss of American beech trees has diminished timber supply and deprived small animals like chipmunks, squirrels and blue jays which depend on beech nuts as a source of food.