In Wisconsin and the U.S. we've been fighting an uphill battle since Dutch Elm Disease disease was introduced in the 1930s. Dutch Elm Disease (DED) is caused by a fungus called Ophiostoma ulmi. The American elm, Ulmus americana, is extremely susceptible to Dutch Elm along with all European elms. Since the 30's we have lost hundreds of thousands of elm trees across their native range. These majestic giants of our urban canopy went from being a dominant tree along our streets, parks and homes to being a rare specimen. The few large survivors we have deserve a high level of care to preserve and protect them.
The Dutch Elm Disease fungus is primarily spread by the native or European Elm Bark Beetle. This beetle flies from canopy to canopy feeding on broken branches or open wounds caused by storms or improperly timed pruning on elm trees. As it feeds the fungus is transferred into the vascular system of the tree. When this happens the tree attempts to fight off the pathogen by blocking off the vascular system to prevent further spread. Unfortunately the elms' self-defense mechanisms essentially overreact and end up plugging the vascular system closed, starting at the the point of infection and spreading in short time (weeks to months) throughout the entire tree.
The symptoms are easily spotted during the spring and summer. Look for individual branches with leaves turning gray to brown in the canopy. If you see and report this to a Certified Arborist, the arborist will take a sample and look for brown staining in the vascular system. If there's any question as to the cause, the sample must be submit it to a tree lab for testing.
Generally, if you are seeing symptoms, it is already too late to save your elm tree. This is why consistent, preventative treatment for the nicest elm trees is very important.
Property owners who choose preventive or therapeutic treatment for an elm tree general hire a Certified Arborist. The arborist will make several measurements and canopy calculations, then hook the tree up to infusion system (analogous to a human I.V. at the hospital) and deliver a chemical treatment (Arbotect 20-s) to the vascular system where the chemical will be carried throughout the canopy. This treatment will protect the tree for three years from the time of treatment and is the only recommended treatment with a regular success record.