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DUTCH ELM DISEASE MAKES A RETURN

Several years ago this column speculated that we were going through another round of Dutch elm disease. Traveling along any of Western New York's highways, dead trees in the traditional vase shape of the American elm are everywhere.

Now, from the Morton Arboretum, comes word that a newer, more virulent strain is out there. In recent years the more aggressive strain has been spreading across the United States, according to Karel Jacobs, plant pathologist.

"A newer strain of the Dutch elm disease fungus, Ophiostoma novoulmi, is likely the cause of the recent outbreaks of the disease," she said. "This stronger strain of the disease-causing fungus, along with less vigilant monitoring and cleanup of diseased trees, has caused a resurgence of the disease."

Dutch elm disease began to kill trees in the 1930s and destroyed hundreds of thousands of trees. It affected mostly American elms and caused more than $1 billion in damage. The younger generation of Western New Yorkers doesn't even remember what our tree-lined streets looked like years ago.

To refresh those who have forgotten and at the same time teach those too young to recall, Dutch elm disease is primarily spread by beetles -- the native elm bark beetle and two species of European bark beetles. They feed on twigs and upper branches in the spring, carrying the fungus with them. The fungus is also taken by the beetles to fresh wounds (pruning and otherwise).

Eggs laid by the beetles hatch into larvae that tunnel under the bark and create even more pathways for the fungus to spread until it clogs the water-conducting cells of the tree. Branches begin to wilt, and before long the tree is dead.

The disease also spreads through root grafts in the soil. Trees growing within 20 feet of each other have a 100 percent chance of roots crossing and grafting each other. The fungus simply crosses over from one tree to the other.

To prevent the spread of the disease next spring, the Morton Arboretum recommends that homeowners do the following:

Since the fungus-carrying beetles breed in standing dead or dying elm trees, trees that wilt and die should be removed.

Bark beetles can also breed in piles of elm wood with the bark attached. Infected wood and bark should be destroyed by burying, chipping and composting, burning, or at the very least removing the bark from the logs and letting them dry.

Do not keep cut logs from diseased trees as firewood unless all of the bark has been removed.

Do not transport elm wood to other regions as it risks moving the disease to another location.

Homeowners with particularly valuable elms should consult with local arborists on the latest chemical treatments to protect healthy trees.

There has been a great deal of work done in an attempt to breed disease-resistant elms and some of it has been done at the Morton Arboretum. The "Accolade" elm, a cross between a Japanese elm and a Wilson elm, is the result of the work done by George Ware, a research associate. It displays many desirable characteristics:

Resistance to Dutch elm disease

Resistance to elm leaf beetles

Appearance similar to American elm

Tough branches and wood

Good fall color

Emerging reddish foliage

Climate hardiness

Planning on being in the Chicago area anytime soon? Take time to visit the Morton Arboretum. There are 1,700 acres featuring 30,000 labeled plant specimens representing 3,600 different types of plants from all over the world. Can you think of a better way to spend a sunny summer day?

A lone cherry tree

Q. For four years my cherry tree has had hundreds of flowers, but the cherries soon shrivel and dry to the size of a pea. Some folks have suggested frost, but there was no frost this year. I have sprayed with captan and lime sulfur. The tree is 12 inches in diameter and about 15 years old. -- O.B. Cheektowaga

A. You didn't mention what type of cherry tree. Sour cherries do not need two varieties to pollinate but sweet cherries do. Was there another tree removed from your yard or possibly from another yard nearby? If your tree is a sweet cherry, it could be that your "pollinator" is gone. Some fruit trees did suffer from a late freeze in April. Normally a freeze that early is not a problem but because spring broke so early it could still have been a factor.

Should it happen again next season, I would suggest you contact the Cooperative Extension office in Lockport. Since that region of the state grows a great deal of fruit trees, their staff would be better able to help solve your problem.

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