156 



Ii.i.ixois Natural History Survey Bulletin 



Vol. 27. Art. 2 



Plant pathologists of the Illinois Natural History Siir\'ey culturing sample of American elm 

 susjiected of being affected by the Dutch elm disease. Modern laboratory equipment enables the 

 plant pathologists to substantiate field <iiagnoses. 



Urbana in 1951. The numbers of affected 

 trees in succeeding years in Champaign 

 and Urbana were 11 in 1952, 164 in 

 1953, 694 in 1954, 1,805 in 1955, 1,836 

 in 1956, and 2,116 in 1957. These 6,627 

 diseased elms represent over 44 per cent 

 of the elm population of Champaign and 

 Urbana when the disease was first found 

 there. 



The Natural History Survey has had 

 one full-time plant pathologist conducting 

 research on elm diseases, including Dutch 

 elm disease, since July, 1951 : Ralph W. 

 Ames in 1951 and 1952 and Richard J. 

 Campana in 1952 and later. 



Oak Diseases. — Numerous inquiries 

 about diseases of oak during the 1930's 

 led to a special investigation which culmi- 

 nated in the publishing of a preliminary 

 report (Carter 1941). Although a dozen 



fungi were associated with the develop- 

 ment of canker and dieback diseases of 

 oak in the field, only one fungus, Dothio- 

 rella querdna, caused canker and die- 

 back under controlled experimental con- 

 ditions. The other organisms appeared to 

 produce canker and dieback only on trees 

 previously weakened by adverse growing 

 conditions. 



Oak wilt, the most destructive and 

 widespread disease of oak trees in the 

 United States, was not found in Illinois 

 until 1942, when a few affected trees 

 were discovered in Ingersoll Park at 

 Rockford in Winnebago County. In fol- 

 lowing years the disease was found in 

 other counties; by 1958 it was killing 

 trees in 70 of the 102 counties of the state. 



Extensive research on the disease was 

 started in 1950 with a grant of money 



