DUTCH ELM DISEASE IN ILLINOIS 13 



Variations in resistance to Dutch elm disease are indicated to 

 some extent by the number of elms that have survived on the Uni- 

 versity of Illinois campus in Urbana. The first recorded instance of 

 Dutch elm disease on the campus was an infected American elm ob- 

 served in June 1951. From then to 1967 the disease killed 1,606 of 

 2,196 American elms (559 were killed by phloem necrosis, a virus 

 disease), 1 of 52 Chinese elms, 12 of 14 slippery elms, 1 of 3 Holland 

 elms, and both of 2 rock elms. 



Other elms on the campus (in limited numbers), none of which 

 have been killed by Dutch elm disease, are Camperdown, globe, 

 Huntingdon, Jersey, Siberian, smooth-leaved, and Wych elms. 



DISEASE CONTROL PRACTICES 



Although no treatment is known that will cure Dutch elm dis- 

 ease, annual losses caused by the disease can be maintained at a very 

 low level by a program of sanitation, spraying with an insecticide, 

 and treating grafted roots with a soil sterilant when elms are growing 

 close enough together so that root grafts occur. 



Sanitation 



Sanitation is a basic procedure for a successful control program, 

 so important that spraying without sanitation is not recommended. 

 Beetle-infested elm material found between May 1 and August 1 

 should be disposed of immediately or sprayed with DDT. A spray 

 of DDT, 1 percent, in No. 2 fuel oil will prevent fungus-infested 

 beetles from escaping and carrying the fungus to healthy trees. (This 

 spray is inflammable until thoroughly dry, and it will kill vegeta- 

 tion.) Beetle-infested material found after September 1 should be 

 disposed of by May 1 of the following year. 



A sanitation program is likely to fail if it is based on the destruc- 

 tion of only those elms that are shown by laboratory culturing to be 

 infected by the Dutch elm disease fungus. Bark beetles lay eggs and 

 produce offspring in elms that are weakened or dying, or that have 

 been recently killed by disease, drought, lightning, excavation, or 

 other mishaps. They may also lay eggs and produce offspring in elm 

 stumps and in elm logs in woodpiles. Bark beetles infested with 

 spores of the Dutch elm disease fungus will carry the spores into the 

 galleries in which they lay eggs. The fungus will grow throughout 

 the galleries and the young bark beetles that later emerge from this 

 infested wood will carry the fungus to any trees upon which they 

 feed. Therefore, effective sanitation is the careful, thorough, and 

 prompt removal (cover photo) and proper disposal of all elm trees 

 and other material in which bark beetles can colonize. This material 



