CEPHALOSPORIUM WILT OF ELMS 21 



been attacked by leaf-feeding insects and bark beetles. Therefore, taking into 

 consideration the significance of wounds in the present experiments, it would 

 appear that insects infesting leaves or bark could transmit the causal fungus 

 in much the same manner that the fungus associated with the Dutch elm disease 

 is transmitted. Hence the reports by Becker (5, 6) in 1935 that Hylurgopinus 

 riifipes Rich., a native elm bark beetle, invades living cambium may have particu- 

 lar significance in connection with the spread of the Cephalosporium fungus. 



The wide variability of the cultures of Cephalosporium sp. which has been 

 observed by the writers, together with the fact that both the present experiments 

 and those of Creager have been carried out with fungi isolated in New England 

 as opposed to the experiments by Goss and Frink with fungus cultures isolated 

 in Nebraska, gives rise to the suggestion that the organism used by Goss and 

 Frink may be a different strain or even a different species from those used by 

 Creager or the writers. 



The experiments conducted b\- the writers concerning the pathogenicity of 

 the various strains of the fungus are indicative rather than conclusive. That 

 the strains tested do grow in the host is evident, but to determine the relative 

 pathogenicity of the various strains, or to separate, definitely, one strain from 

 another, would require much more time and considerable careful study. The 

 problem is one of great interest, but is, necessarily, outside the scope of the 

 present study. 



CONTROL MEASURES 



With present knowledge, it is impossible to distinguish accurately the relative 

 value of applied control measures, tree vigor, and what might be considered 

 inherent resistance to the disease. Certainly some resistance might be expected 

 in the case of a disease caused by a fungus which has been associated with the 

 host over an exceedingly long period of years. 



Not all elms affected by the disease exhibit evidence of serious damage. The 

 presence of Cephalosporium in a vigorous tree is a condition met with rather 

 frequently. On the other hand, the fungus is known to cause progressive death 

 of tree parts annually and may even kill entire trees. Nevertheless, certain trees 

 from which the causal fungus has been isolated have apparently recovered; 

 and other trees from which the fungus has been cultured have been observed as 

 free from disease symptoms when the trees were growing in shad}' places, along 

 streams, or under favorable arboricultural conditions. Also, the progress of the 

 disease appeared to be limited, under greenhouse conditions, in trees infected 

 with a second wilt-inducing fungus, Verticillium sp., in addition to Cephalosporium 

 sp., since trees infected with both of these fungi did noc die back so rapidly as 

 trees infected with either one of the fungi alone. Experiments involving inocula- 

 tions of one tree with two different genera of fungi were not a part of the formal 

 experiments previously discussed but were undertaken independently following 

 similar observations in nature. For the most part experiments in the greenhouse 

 on the control of this fungus and the wilt disease associated with it have been 

 limited to the cutting out of diseased portions of trees. Similarly individuals 

 have reported some success in treating diseased trees in the field by careful 

 pruning, treating of wounds and scars, and judicious watering and feeding. 

 Some trees apparently respond much more readily than others to the suggested 

 treatment. 



Individuals interested in constructive experimentation on trees affectea with 

 Cephalosporium wilt have been advised to try the following procedure: 



