(\:>r.oRAi)() Pr.ANT Diseases 
41 
which when injected into the plant brings about the diseased condi- 
tion. The insect gets this substance into its system by biting a 
diseased beet. A leaf hopper which has never been upon a diseased 
plant may bite a healthy beet without producing the disease, but if 
it is on a diseased beet before it bites a healthy one the disease 
will follow. 
It has recently been shown that a number of other plants in- 
cluding a few common .weeds may also be affected with curly top. 
A leaf hopper from such a plant may carry the disease to healthy 
beets. It is probably in this way that the disease lives over the 
winter. Curly Top is a difficult disease to control. The destruction 
of the leaf hopper would probably reduce the amount of curly top 
but this is not very practical. 
Rhizoctonia root-rot of sugar beet. 
Curly dwarf of sugar beet. 
(After Townsend.) 
