A Cure for Elms

Each year more and more American elm trees, which once lined hundreds of town squares, fall victim to Dutch elm disease. Last year the apparently incurable blight destroyed at least half a million trees in the U.S. This summer the pestilence may be worse; it has spread from the East through the South and Midwest and is now attacking trees as far west as Denver.

After every other remedy failed (including such folksy "cures" as injecting trees with turpentine or whacking galvanized nails into their trunks), scientists believe they have found a way to stop the fungus that causes the disease and the elm-bark beetles that spread it. The new approach involves two steps: spraying dormant elms in early spring with a pesticide called methoxychlor, which is lethal to the beetle but harmless to most other insects, and then spraying again in June with a chemical called Benlate, which attacks only the fungus. Instead of spraying, the arborist may also inject Benlate directly into the tree trunk, which puts the fungicide into the elm's circulatory system. After testing the treatment on 600 elms in a Milwaukee suburb for two years, University of Wisconsin researchers report that the mortality rate for the trees has dropped from 5% per year to 2% .

Benlate itself is not completely new.

For two years it has been used as a fungicide to protect roses and tomatoes. What is new--officially approved only this March by the U.S. Department of Agriculture--is its application to Dutch elm disease. The problem now is to persuade communities and private tree owners to undertake the effort and expense ($75 per tree per year) needed to make the treatment work. When John Hansel, executive director of the Elm Research Institute, took the cure to Denver last February, the mayor refused to see him. The city had its own method for treating the disease--simply cut down and burn infected trees. Says Hansel: "We've come a lot farther in dealing with the beetle than we have with the politicians."

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