Dutch elm disease is very difficult to control once infection has begun. If Dutch elm disease has been diagnosed, tree owners, with the assistance of a certified arborist, should determine the extent of infection to see if curative treatments have any chance of working.
Therapeutic pruning should be considered. In some cases the disease can be pruned out of the tree if there are only a few infections and they are detected early. At the first indication of a symptomatic twig, the infected branch to which it is attached should be removed and destroyed. Prune back at least 10 feet into healthy wood, usually to a major limb. If internal discoloration or streaking is noticed in the pruned wood, cut back another 10 feet. Trees that are showing dead leaves and branches in more than 5-10% of the crown may be so thoroughly infected that the tree is not going to survive anyway and the entire tree will need to be removed and destroyed.
Injecting elm trees with fungicides for Dutch elm disease control can be successful if done before the disease starts, or where therapeutic pruning has been used. However, injections are a waste of money if used after the tree is fatally infected or in communities with many infected trees and lacking community-wide Dutch elm disease control programs. Injections usually fail where sanitation, pruning, and insect control are not practiced. In addition, injection is physically damaging to the tree, because it results in wounds where discoloration and decay can occur. Therefore, use injections mainly for prevention and where they will not have to be used year in and year out. Retreatment of already infected trees may be necessary. Homeowners should enlist the aid of a certified arborist who has been trained to inject for Dutch elm disease control.
