The American elm tree used to be one of our most widely planted shade trees. For generations, its stately vase-like form and arching branches added charm to the streets of cities and villages. In 1930, Dutch elm disease showed up in Ohio. It had been brought to this country on veneer logs imported from Europe, and since then has spread north and south, east and west, to wherever the American elm was grown. Millions of these fine trees were killed, thousands of them in Washington. Massachusetts lost more than 150,000 trees in 20 years. Rockford, ILL., has spent more than $1 million to cut down dead trees.
A lot of American elm trees are still living, having been saved by spraying them to eliminate the bark beetles that spread the disease, and by injecting them with certain fungicides to save them even after they have become infected.
One of the first fungicides used for injections was Benomyl. Apparently the fungi developed resitance to it. Now Arbortect is being used and continues to be good, according to specialists. Lingnasan BLP is rated by some as being the best at this time. Both Arbortect and Lignasan BLP are available at some garden-supply stores.
According to the Elm Research Institute, on organization pledged to save the American elm from extinction, dead or dying trees must be removed completely at ground level and wood properly disposed of, and all dead wood of elms must be pruned promptly and the wood burned or buried to get rid of the bark beetles; a dormant spray of Methoxychlor should be used to kill the beetles before they can cause infection, and if should be injected with Lignasan BLP.
In their 1978 Fall Progress Report the institute said that in Baltimore 600 healthy municipal trees were treated preventively without a single loss; in Riverside, ILL., 1,079 healthy municipal trees were treated for three years without a single loss; in Detroit, 485 healthy municipal trees were treated for three years without a single loss; and, in Minneapolis, in spite of a raging epidemic of the disease which in a single year cost the lives of 82,000 American elms in the Twin Cities, 28 healthy trees which have been under preventive treatment for 7 years still are healthy.
The obvious conclusion: Preventive treatment (sanitation, spraying and injecting) saves trees.
But there is a fly in the ointment. Dr. Alex Shigo, chief scientist of the USDA Forestry Sciences Laboratory, Durham, N. H., says the injection can do a lot of damage to the trees unless made properly by people who know exactly what they are doing.
"I feel that the injection method does show great promise and that we can use the method to benefit trees," he says, "but only if the method is used properly. It involves putting a hole into a tree, and when we put a hole into a tree we have a wound. You can only put so many holes into a tree before internal trouble starts. Next we must be careful what materials we put into the tree. Many chemicals and carriers kill living cells in the wood. You can only put so many holes into a tree before serious internal trouble will start.
"You can inject for several years without getting into too much trouble, but after five or six years the trees will begin to have troubles.
"The injection wound should be made as small as possible. There is no need to go deep into the wood.The depth of the wound should be as shallow as possible. Avoid making holes into trees with dull tools. The wound should be as low on the trunk as possible. Most important of all, do not wound trees annually. Annual injections will lead to real problems. If people do not believe this, they should see what has happened to some of our sugar maple trees that have been tapped repeatedly."
There is an additional problem. Phloem necrosis, another disease of American elms perhaps even more deadly than Dutch elm disease, is spreading. It has been reported in New England, and it seems likely it soon will be found in most, if not all, of the native range of the American elm. There is no known cure for it.