December, 1958 Carter: Applied Botany and Plant Pathology 



155 



sion of the tree disease research program 

 in 1950, additional plant pathologists 

 were added to the staff. The recent re- 

 search program has been carried on by four 

 plant pathologists, Richard J. Campana, 

 Walter Hartstirn, Eugene B. Himelick, 

 and Dan Neely. 



In the studies on the cause and control 

 of the wilting of elms, it was found that 

 several fungi w'ere involved. Although 

 the first report on this work (Harris 

 1932) indicated that several fungi were 

 capable of causing the wilting, later 

 studies showed that most wilting was 

 caused by the Dothiorella wilt fungus 

 and it was most serious in plantings of 

 trees that were weakened by overcrowd- 

 ing and by repeated annual defoliations 

 from heavy infestations of the spring 

 cankerworm. Spraying with copper and 

 sulfur fungicides was not effective in 

 noticeably reducing or preventing wilting. 

 This spraying included dormant and foliar 

 applications, in some years as many as one 

 dormant and seven foliar sprays. Al- 

 though research failed to find a control 

 for this type of wilting of elms, it showed 

 that applications of either sulfur or cop- 

 per fungicide in June and early July gave 

 excellent control of the black leaf spot 

 disease (Trumbower 1934). Control of 

 this disease in commercial nursery plant- 

 ings of elms increased the annual growth ; 

 sprayed trees made as much growth in 

 4 vears as unspraved trees made in 5 

 years (Carter 1939). 



A conspicuous and widespread dying of 

 elms which became evident in Danville 

 and Peoria in the late 1930's appeared in 

 other areas in succeeding years. It now is 

 widespread and destructive throughout 

 the southern two-thirds of the state. 

 North of Peoria, Bloomington, Cham- 

 paign, Urbana, and Danville, it occurs 

 in only a few isolated places. The north- 

 ernmost isolated infection is in Rockford. 

 This disease, called phloem necrosis and 

 described as a virus disease in 1942 

 (Swingle 1942), has killed thousands of 

 elms in Illinois and is one of the two 

 major diseases that continues to kill thou- 

 sands of elms annually. In Champaign 

 and Urbana phloem necrosis killed 2,460 

 trees in a period of 14 years; this number 

 represents over 16 per cent of the total 

 elm population in the two cities. Mount 



Pulaski, with an elm population of ap- 

 proximately 600 trees in 1940, had all 

 but 19 elms killed by the disease by Sep- 

 tember of 1948. 



During the late 1930's and early 

 1940's, in investigations of the wilting 

 and dying of elms, several fungi capable 

 of producing cankers were studied. Can- 

 ker diseases usually were confined to a 

 few trees in a planting of elms but were 

 found in plantings in widely scattered 

 locations in the state. The cankers caused 

 bv species of Cytosporina, Phoma, and 

 Coniothyrium were prevalent only on 

 American elm. The canker caused by 

 Tubercularia ulrni affected the Asiatic 

 species of elm, Ulmus pumila and U. 

 parvifoUa. 



A serious and widespread wilting of 

 elms in Hinsdale was brought to the at- 

 tention of the Natural History Survey by 

 Village Forester W. E. Rose in 1939. 

 Intensive research on these elms resulted 

 in the discovery of a bacterial disease 

 called wetwood (Carter 1945). Wet- 

 wood is a chronic disease that affects most 

 elms but usually does not result in the 

 death of affected trees. Ulmus pumila is 

 especially susceptible to wetwood. Re- 

 search on this disease is described in a 

 42-page article under the title "Wetwood 

 of Elms" (Carter 1945). The National 

 Arborist Association awarded a citation 

 to the author in "recognition of his ex- 

 cellent work" reported in the article. 

 This work the Association "considered 

 the outstanding research during 1945 on 

 shade tree preservation." 



Dutch elm disease is the most destruc- 

 tive disease of elms in Illinois. Although 

 this disease was first discovered in the 

 United States at Cleveland and Cincin- 

 nati, Ohio, in 1930, it was not until 1950 

 that the first diseased elm was found in 

 Illinois. Only one tree affected with 

 Dutch elm disease was found in 1950, 11 

 were found in 1951, 24 in 1952, and over 

 500 in 1953. The numbers of counties in 

 which the disease has been found each 

 vear were 1 in 1950, 4 in 1951, 9 in 1952, 

 15 in 1953, 55 in 1954, 74 in 1955. 86 

 in 1956, 94 in 1957, and 99 in 1958. The 

 rapid destruction of elms by the disease 

 is illustrated by the numbers of trees af- 

 fected each year in Champaign and Ur- 

 bana. Onlv one affected tree was found in 



