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When we moved back to a farm in 1975, we were faced with 27 stumps of what were once beautiful elm trees that had been decimated by Dutch elm disease. This summer has been another bad one for the disease. You only have to look along the tree line and one can spot the brown trees among the lush green ones.

Everyone connected with gardening has heard of Dutch elm disease. I thought the disease was a recent problem. According to Michelle Grabowski, Regional Extension Educator, the disease has been around since the 1930's. This is when the fungus that causes this disease was first introduced to North America.

The fungus originated in Asia, made its way to Europe. This is where it picked up the name "Dutch" elm disease. When it arrived in North America it became a much more aggressive pathogen, which we are dealing with today.

American elms are highly susceptible to the Dutch elm disease fungus. The fungus infects the vascular system of the tree. This blocks the flow of water from the roots, resulting in wilted leaves and eventually death of the tree.

Trees can become infected in two ways:

One way is the elm bark beetles lay eggs in diseased trees. When the new beetles emerge they will carry sticky spores stuck to their bodies. These beetles then feed on healthy elm trees, bringing the fungus along with them.

The other way is the diseased tree can pass the infection to a healthy neighbor through root grafts, which is a natural connection formed between two trees that are within 50 feet of one another.

Infected trees will first show one to a few flagging branches. These branches will have wilted and yellow leaves that will eventually die and turn brown, but remain attached to the tree. The infection causes visible brown staining of the sapwood that can be seen if the bark is peeled off infected branches. It is possible to prune out diseased branches to stop the disease, if it is caught early enough. The fungus is actually deeper in the tree than the staining indicates. Therefore, the branch must be cut 10 feet from where the last sign of staining can be seen. This will remove the fungus from the tree, but new infections may occur at a later time.

The best way to prevent Dutch elm disease is to protect them with preventative fungicides. Trees are treated in a process called macro infusion. Small holes are drilled in the widening base of the trunk of the tree. Plastic tees and tubing are used to carry the protective fungicide to these holes and into the trees vascular system. One macro infusion treatment will protect a tree for one to two years depending on which fungicide is used. Treatment can protect a tree from spores transmitted by beetles, but not against infection caused through a root graft. Although treatment will not cure severely infected trees, they can be used in combination with pruning of infected branches to save a recently infected tree. These treatments should only be done by a certified arborist.

Many people do not realize that the fungus continues to grow and survive in the tree after it has been killed. If a tree is infected by Dutch elm disease to the extent that more than a few removable branches are infected, the entire tree should be removed as soon as possible. Once cut down, wood from the diseased tree must be debarked, burned, buried, or cut into woodchips. Logs with bark that are left for firewood or other uses will continue to support both the fungus and the elm beetle, and will therefore continue to add to the disease epidemic.

Many elms killed by Dutch elm disease are not properly disposed of. Therefore, the elm bark beetle population has been able to grow and the disease has continued to spread.

Probably the best hope for a future of healthy elm in America is the development of disease resistant cultivars and hybrids. There are several Dutch elm disease resistant elms available today. None are completely immune but rather considered to be highly resistant.

You can view the entire article as well as information on disease resistant varieties at:http://www. extension.umn.edu/projects/yardandgarden/ygline-news.html.

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PLANT CLINICS: Volunteer Master Gardeners will be available Mondays, from 4:30-7 p.m., at the Extension Office in North Branch, at 38780 Eight Avenue, to answer your gardening questions.

You can also call 651-674-4417 during these hours to speak with a Master Gardener.

Samples can be dropped off during the day on Monday if you cannot stop in during clinic hours. Please note: MONDAY is the only day you can drop off samples, as there is no longer staff at the North Branch Office who can answer gardening questions.

VOICE MAIL: You can leave a question for a volunteer Master Gardener at 651-674-4417. Depending on the volume of calls, they try to respond within a couple of days. During office hours ask for the Master Gardener voicemail, after hours, select ext. 18. You can also get your question answered on the web at: www.extension. umn.edu/askmg.

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