VEGETABLE AND FIELD CROPS 213 



The bacteria may also travel upon seed from diseased 

 localities, infect the young plants, and initiate an epidemic 

 in a new locality. Diseased plants shipped across the 

 country also carry infection. 



The disease may be carried from field to field in any 

 diseased plant part or in infected soil, upon tools, feet, etc., 

 and especially in manure that has become infected by the 

 use of diseased plants as cattle feed. To avoid carrying 

 the disease to near-by fields all the precautions suggested 

 under soil diseases must be employed. 



It has as yet been impossible to kill the bacteria in the 

 soil. The only recourse is such crop rotation as will avoid 

 the planting of any susceptible crop upon infected soil for 

 a period of several years. Just how long the bacteria can 

 remain alive in the soil is not known. In practicing crop 

 rotation for elimination of this pest all cruciferous weeds, 

 mustard, shepherd's purse, etc., must be avoided, since 

 they are susceptible and harbor the disease just as effec- 

 tively as would cabbage. 



Since the seed may bear the bacteria, it is well to soak 

 them for fifteen minutes in corrosive sublimate one 'part, 

 hydrochloric acid two parts, water one thousand parts, or in 

 formalin one pound to thirty gallons of water, to kill these 

 germs and thus avoid introducing the disease into new 

 localities. If this had been done, many counties now so 

 infected as to prohibit cabbage culture would still be free 

 from this pest. 



Club root (Plasmodiophora brassicae Wor.). — Club root 

 is widely known, very destructive, and easy of recogni- 

 tion. It consists of a greatly enlarged growth of the root, 

 either the main root or the lateral roots, or both, as is 



