CoL()]{Ai)o Plant Disioases 
69 
evei\ are not always effective. Learn to recognize the disease if you 
see it and I’eport all suspicious cases to the Agricultural College. 
PLUM 
Plum Pocket (Taphrina communis) (67)— This is a common and 
serious disease of the plum in Colorado. Affected fruits first turn 
yellow followed by a rapid enlargement to several times the normal 
size. The surface becomes wrinkled and the pit fails to develop 
being replaced by a large empty cavity. The diseased fruit later 
turns brown, shrivels and may fall off or remain attached to the 
tree for some time. The entire crop may be destroyed in this way. 
Plum pocket is caused by a fungus which infects the young fruit 
as soon as it is formed causing it to make the abnormal growth 
described above. Where and in what condition the spores live over 
the winter is not definitely known, but it has been demonstrated that 
the disease can be controlled by spraying with lime sulfur. Either 
the factory or self boiled solution may be used. Only one application 
is necessary. It should be applied in late winter or in early spring 
before the flowers begin to open. 
Shot-Hole — see Cherry. 
Crown Gall — see Apple. 
Black Knot — see Cherry. 
POPLAR 
Canker (Cytospora chrysosperma) (68)— Various species of pop- 
lar and willow are important in Colorado as shade and ornamental 
trees. In the more arid sections no other tree will make a satisfactory 
growth. Large numbers of these trees have been killed in the past 
few years by the canker disease. This is especially true in the 
southern half of the state. 
Canker affects the twigs and large branches of the tree. The 
most prominent sign of the disease is the red gummy substance that 
is excreted over the surface of diseased branches in the form of 
slender thread-like coils or small red dots. 
The disease is caused by a fungus that usually infects the plants 
through wounds of some sort. 
Small branches are usually the first to die and the disease spreads 
rapidly from these down to the main trunk which is eventually 
girded, killing the entire tree. Shoots or suckers often put up from 
the ground after the upper part of the tree is killed. 
Colored Plate on opposite page illustrates the poplar canker, 
rado State Entomologist’s Annual Report for 1919. 
Original used in Colo- 
