This practice has little effect on overall disease incidence. Consider systemic fungicides only when an effective sanitation program also is in place to prevent new infections. These fungicides do not kill the DED fungus, but only keep the disease in remission. Repeat applications to ensure continued protection. Furthermore, the high cost and erratic performance of the treatments make them suitable only for very high value trees.
Injections produce considerable wounding.
Pruning When insect-caused DED infections are detected early, prompt pruning can prevent spread of DED throughout a tree. If less than 5 percent of the crown area shows the flagging symptoms of DED infection, pruning at least 10 feet below the area on the branch showing discoloration may salvage the tree. Trees treated in this manner require close inspection in the future. Resistant Varieties Researchers have worked for years to develop elm varieties that are resistant to Dutch elm disease. These are primarily crosses between various Asiatic elms and American elms.