168 



Diseases of Economic Plants 



ceptible and harbor the disease just as effectively as would 



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

 them for fifteen minutes in formalin, one teaspoonful to a 

 half pint of water, to kill these germs and thus avoid in- 

 troducing the disease into new iocahties. If this had been 

 done in earlier years, many 

 counties now so infected as to 

 prohibit cabbage culture would 

 still be free from this pest. 

 Resistant varieties will do 

 much to solve the problem. 



The cauliflower is affected 

 in much the same way as the 

 cabbage. Local infection in 

 the head often produces the 

 effect shown in Fig. 90. 



• Club-root 2««-2ii' 227 (^pias- 

 modiophora brassicce Wor.) . — 

 Club-root is practically of 

 world-wide distribution, and 

 destructive to cabbage, kale, 

 cauliflower, turnip, rutabaga, 

 collards, Brussels sprouts, 

 radish, stocks, candytuft, sweet 

 alyssum, and upon wild crucif- 

 erous plants, shepherd's purse, 

 peppergrass, pennycress, black 

 mustard, charlock, false flax, 

 hedge mustard. It may readily be recognized by the en- 

 larged growth of either the main root or the lateral roots, or 

 both, as shown in the accompanying figure. It cannot be 

 confounded with any other disease unless that caused by 

 eel worms (nematodes), and from this it may easily be dis- 

 tinguished by the larger club-root galls. 



These swellings may be noted in the seed bed, though they 

 are usually overlooked until they enlarge in the field. They 



91. — Cabbage club-root. 

 Original. 



