DUTCH ELM DISEASE IN ILLINOIS 19 



Pruning. Pruning infected branches will eliminate the Dutch 

 elm disease fungus if it is confined to the portion of the branch re- 

 moved. However, by the time most elms show wilt symptoms the 

 fungus most likely has spread into the larger branches or the trunk. 

 When this has occurred the fungus will not be eliminated by pruning. 

 Also, pruning gives no protection to the rest of the tree. Pruning for 

 Dutch elm disease control is not recommended as a general procedure. 



Internal medication or chemotherapy. Research on the intro- 

 duction of chemical compounds into elms for protection against 

 Dutch elm disease began about 1940, and since then thousands of 

 compounds have been tested. The types of materials tested include 

 insecticides, fungicides, antibiotics, repellents, and growth regulators. 

 In much of the early research inorganic compounds were tested. In 

 the more recent research mainly organic compounds with systemic 

 properties (capable of killing the fungus or insects when carried in 

 the sap) have been tested. Although some of these materials have 

 shown promise of protecting healthy elms against the disease, more 

 research is needed before any of them can be recommended. 



One chemical compound currently publicized for the control of 

 Dutch elm disease is the systemic insecticide Bidrin. Experimental 

 testing of this compound for Dutch elm disease control started in 

 1958. The results obtained by the various states and the U.S. De- 

 partment of Agriculture Forest Service are not in agreement. In 

 1965, the results reported by some research workers indicated ef- 

 fective control while the results reported by others indicated none. 

 After careful consideration of the available data from the federal 

 government and the various states, the Natural History Survey 

 does not recommend the use of Bidrin for the control of Dutch elm 

 disease. 



THE DUTCH ELM DISEASE LESSON 



Because trees are living plants, subject to many hazards which 

 will impair their value or cause them to die, a tree care and replace- 

 ment program is necessary to maintain the trees needed for shade 

 and ornamental purposes. 



The spectacular loss of elms from Dutch elm disease empha- 

 sizes the importance of planting a variety of trees to avoid similar 

 catastrophes in the future. It is suggested that any one kind of tree 

 should not represent more than 10 percent of the total tree popula- 

 tion of a planted area. Many species and varieties of trees are avail- 

 able for shade and ornamental purposes. Information on trees 

 suitable for these purposes is given in Natural History Survey Cir- 

 cular 51, "Illinois Trees: Selection, Planting, and Care." 



