APRICOT DISEASES 157 



CROWN-GALL 



Caused by Bacterium tumefaciens E. F. Smith and Townsend 



In California this disease has been troublesome for many 

 years. Since 1880 it has been the subject of inquiry and writing, 

 with reference particularly to its cause and control. In recent 

 years the .question of crown-gall on a great variety of plants has 

 been illuminated, and the more important phases of the disease 

 have been carefully studied. (For a fuller discussion of the 

 disease, see under Apple, page 108.) 



GUMMOSIS 

 Caused by various factors 



The formation and exudation of gum is a phenomenon to 

 which the apricot, like other stone-fruit trees, is subject. Gum- 

 mosis, or gum-flow, is the result of injury due to such factors 

 as mechanical abrasion, unfavorable climatic conditions, bacteria 

 and fungi. (See Cherry, page 181, and Peach, page 303.) 



DIE-BACK 



There appear to be at least two distinct die-back diseases, 

 one in California, which is regarded as being due to a lack of 

 water and other factors, and the other has been described from 

 Missouri caused by the fungus Valsa leucostoma var. rubescens. 

 The latter type also exists in Texas, New York and doubtless 

 elsewhere. The California trouble is evidenced by a dying 

 back of the branches of apricots and almonds. The middle- 

 western and eastern disease shows as cankers on the southwest 

 side of trees. In this connection sun-scald, or late winter- 

 injury, is suggested ; and it is not unlikely that temperatures 

 do play a part in bringing about the disease. Large branches 

 die, which is a symptom that may cause some confusion in an 



