Barbara Mattson, age 12, of North St. Paul, Minnesota, for her question:

Can the Dutch elm disease be controlled?

In the 1950s, experts hoped to wipe out this elm killing fungus by removing infected wood and spraying the trees with DDT. Maybe they saved a few trees. But each year the Dutch elm disease spread farther eastward and northward. Then we learned that, in some ways, DDT does more harm than good. This dangerous insecticide spreads through the environment, destroying countless harmless creatures. It also threatens human health for, after all, we must share in nature's tragedies.
Dutch elm disease is caused by a minuscule fungus called Ceratostomella ulmi. It is a parasite that thrives in the vessels that carry sap through various species of elm tree. These vessels are grown each spring, just under the bark. The fungus can survive for several years in a living tree and one or two years in dead elm wood. The leaves of an infected tree whither, turn yellow and the disease may spread fast enough to kill the whole tree in a month. Or it may endure a lingering death through four or five years.
Using insecticide to destroy fungus seems like shooting flies with an elephant gun. But researchers had a good reason for this plan. The disease was noticed first in Holland, in 1919. In 1930, it appeared in New York. As American and European scientists tracked its life cycle, they soon learned that the parasite fungus is spread by certain insects. It seemed logical to wipe out these insects to stop the spread of the Dutch elm disease.
The insects involved are tiny bark beetles that spend part of their lives under the bark of elm trees. One is a native beetle who was here all the time. The other arrived from Europe, several years before the fungus parasite. The imported beetle does the most harm. The fungus spores exist inside and on its body. The female tunnels below the bark to lay her eggs. The deadly spores enter the wounds, the fungi develop and the sap carries them throughout the tree. The infected larvae chew more wounds in the tender cells. As adults, they fly off and infect healthy elm trees, often several miles away.
Our native Dutch disease carrier winters under the bark of the elm tree. Before emerging, the adults and nymphs often eat some of the tender wood and take some of the 1971 fungus with them. Neither of the bark beetles needs the fungus    but the fungus does need the beetle to transport it from one healthy tree to the next. No one knows how to wipe out the fungus and, sad to say, no suitable insecticide has been found to wipe out the bark beetles.
Someday no doubt scientists will find a way to control Dutch elm disease. Then the trees will grow back in the elmless regions. In the meantime, we can try to preserve a tree by cutting off infected branches and removing all the littered twigs, leaves and dead wood. It is nice to know that a few elm have survived even in the plague areas.