YOUR GARDEN — Plant Information

Pests, Problems, and Diseases

Dutch Elm Disease

Dutch elm disease is a fatal fungal disorder spread by the elm bark beetle. The fungus can be carried from a diseased tree to a healthy one by the beetle, by the roots of an infected tree grafting together underground with the roots of a healthy tree or by contaminated pruning tools. There is no cure for the disease once a tree is infected.

Susceptible Plants
American elms (Ulmus americana) are the most susceptible to the fungus; Siberian and Chinese elms are more resistant but can still contract the disease. Much research is currently underway to breed disease- resistant elms that still exhibit the much-loved, open-vase shape of the American elm. One such tree is the new Accolade elm introduced by Chicagoland Grows.

Description & Symptoms
The fungus causes the vascular system of the tree to become clogged, preventing the flow of water and nutrients from the soil to the upper canopy of the tree. This manifests itself in the characteristic "flagging" of solitary upper branches, where leaves suddenly wilt; turn off-green, yellow, and brown; curl up; and finally drop off the branches. Homeowners might first notice these symptoms during June, when an "unexplained" dead branch appears high in the tree.

Infected branches will also exhibit brown streaking in the sapwood immediately under their bark. This requires the aid of a professional arborist who should be called in to prune out symptomatic branches for testing.

Damage
The disease can quickly spread to nearby branches of the same tree as well as branches of neighboring elms. If symptoms appear in late summer or early fall, homeowners might confuse the yellow or brown leaves with premature fall coloring. Dutch elm disease can kill smaller trees in one season; large mature trees might succumb in several years.

Because there are other wilt diseases that can produce similar symptoms, homeowners should have their trees tested immediately if they observe such branch dieback. Diseased trees must be quickly removed to prevent spread to neighboring elms.

Treatment & Solutions
There are no chemicals available to homeowners for control of this disease. There are, however, commercially available fungicides labeled to either "prevent" or "manage" Dutch elm disease; but they must be sold to and applied by licensed applicators only. These products are injected into the tree at a cost of approximately $300 per injection; and the need for retreatment ranges from one to three years. The fungicides will not be effective in preventing or treating the disease if it is transmitted by interlocking root systems. The chemicals labeled as "therapeutic" or to "manage" the disease are recommended only if the disease has been detected very early.

Research indicates that if less than 5 percent of the tree is diseased, pruning out the infected branches immediately might serve to control the disease. Homeowners with mature, valuable trees who have discovered this disease very early might consider this an option.

Losing mature trees that are over 100 years old is an emotional experience for many homeowners, and some will go to any length to prolong the years they can enjoy their trees. When choosing a large shade tree for parks, lawns or parkways, homeowners are encouraged to plant disease- and insect-resistant varieties and to avoid planting only one type of tree in their neighborhoods.

For those who own American elms, keeping the tree healthy and away from stress is the best prevention. Water elms during drought. Consider deep root fertilization every few years. Avoid growing grass right up to the trunk of the tree. Gently peel back turf to create as large an area as possible (optimally out to the drip line of the tree) where shredded mulch or wood chips can be laid down 2 inches thick. Watch your tree diligently for the first signs of problems: bare branches in the upper canopy, yellowing or dropping leaves in spring or summer, late or stunted growth. Also keep close watch on the health of neighboring elms since the disease spreads quickly through close contact.

For more information about Dutch elm disease, call the Plant Information hotline at (847) 835-0972.