Pests and Diseases 199 



only a few years and the diseases hav'e required time for 

 their spread. New beet areas have each year been 

 opened up and these have been free from disease. The 

 American beet-raiser has come to regard the crop as being 

 free from disease and requiring no attention in this mat- 

 ter. The time of complete freedom from disease, however, 

 has passed. Already the fields in the older districts are 

 infested ; the fight must be taken up in earnest. We may 

 feel thankful for past immunity, but now precautions must 

 be taken to keep in check the diseases that menace the 

 industry. Many fungous and bacterial organisms live on 

 the sugar-beet plant, but only a few are of great economic 

 importance. There are also a number of troubles that 

 seem to be physiological. Forms of rot on tubers in stor- 

 age are shown in Plate XXIII. 



Leaf -spot {Cercospora beticola Sacc). 



This fungous disease is one of the best known and 

 widely distributed of the sugar-beet. It is found in all 

 American beet-growing districts. The amount of injury 

 depends on the number of the fungous plants present 

 and the period in the beet's life when the attack begins. 

 Late plantings are as a rule less affected by the disease 

 than early. It is more injurious to sugar-beets than to 

 the red garden variety. 



It begins as tiny white spots scattered over the leaf, 

 which later develop into small brown spots with a red- 

 dish purple margin. There may be from ten spots to 

 several hundred on each leaf. As the spots become older 

 they turn ashen gray at the center and gradually increase 

 in size until the entire leaf may be covered, when it be- 



