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 Last Update 02/04/07

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Dutch elm disease (DED) is the most devastating shade tree disease in North America.  It is a wilt disease with an extremely high fatality rate among elms.

How Dutch Elm Disease Kills
Dutch elm disease (or DED) is caused by a fungus. After the disease is contracted, spores rapidly reproduce and spread toxins throughout the tree.


The fungus blocks the water-conducting or vascular system of the tree preventing water and minerals from reaching the branches and leaves. The leaves wilt and eventually the tree dies.

The Fungus
The fungus Ophiostoma (Ceratocystis) ulmi attacks various species of elm. It can kill a tree within a few weeks or it can kill it gradually over a period of years. 


There are two strains of the fungus in North America - the non-aggressive strain (O. ulmi) and the aggressive strain (O. novo-ulmi).  While the elm’s natural defense mechanism tries to fight off the fungus, the aggressive strain often moves too quickly for the tree to react without human intervention.

How Long Does It Take for the Fungus to Destroy a Tree?
That depends on the age and health of the tree. A younger fast-growing tree can die quickly. Some younger trees have some natural resistance to DED.  However, this resistance tends to wear off after 15
-20 years.  Slow growing older trees can linger for a year or two.

Is There a Cure for DED?
When an elm tree detects the presence of the fungus, it produces a number of defensive compounds. ‘Mansonones’, for example, are toxic to the DED fungus.  However, left to its own devices, a tree cannot produce enough to fight off the disease.

Researchers are now learning how to stimulate the tree’s natural defenses to produce larger quantities of mansonones. It is a promising breakthrough.  For more information on the new DED treatment,  click here.

For more information on Dutch elm disease, click on one of the topics below:

History of Dutch elm disease Prevention of Dutch elm disease
Transmission of Dutch elm disease Traditional Treatments
Symptoms of Dutch elm disease Innovative Treatment

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