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.) 
Dirt-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 
