Beet Diseases 115 



Crown gall is a very important disease because of 

 its cosnu^litan nature, for it is widely prevalent 

 and attacks a lai^ number of hosts. 



Symptoms. The disease does not usually mani- 

 fest itself until the roots are nearly half grown. 

 Abnormal outgrowths or galls (fig. 16, b.) appear 

 which vary in size from that of a garden pea to 

 nearly two inches in diameter, according to the se- 

 verity of the attack. The galls are usually attached 

 to the beet by a narrow string. In light cases of 

 infecticm there may be but one gall cm the rootj in 

 severe cases, however, the roots may be covered with 

 niunerous galls. 



TTie Organism. The cause of crown gall is a bac- 

 terial organism, Fseudomonas tumefaciens Sm. and 

 Town. It is a short rod, multiplying by fissicm, and 

 moves about by means of poldt flagella. On agar 

 or gelatin it forms small round white colcmies. Un- 

 der unfavorable c«iditi(Mis it readily develops in- 

 volution forms; the organism is short lived in pure 

 culture. P. tumefaciens lives over in the soil frtxn 

 year to year. 



Control. The disease may be introduced with in- 

 fected soil. Sterilizing the soil with steam or for- 

 maldehyde (see pp. 32-43) is reccmmended. 



Scab 



Caused by Actinomyces chromogenus Gasp. 

 Scab on beets is the same as the scab of the Irish 

 potato, the radish, and the carrot. 



