Diseases of Plants 291 



The root-knot disease, which is caused by small " eel- 

 worms," may be confused with the clubroot disease, in the 

 southern states especially. The worms infest the roots 

 and produce swellings, but these are smaller than the 

 swellings of the clubroot. By breaking open the swollen 

 roots, one may often detect pearly white bodies about 

 the size of a pin head ; these are the female eelworms. 



To combat this animal parasite, practice crop rotation, 

 destroy all diseased plants, and clean the frames and flats, 

 as is recommended for the clubroot. 



BACTERIAL WILT OF VINE CROPS 



This disease is caused by a bacterium that lives 

 within the woody vessels which carry sap up to the leaves. 

 This parasite is so minute that many thousands of them 

 can live together within a single cell of the host plant. 

 In time, the vessels are broken down and cavities formed 

 within the host. The supply of water is thus checked, 

 and the plant suddenly wilts and soon dies. There is no 

 recovery and no cure for plants after the germs once get 

 inside. 



The minute germs of this disease are carried from 

 diseased plants to healthy ones by the striped cucumber 

 beetle. This insect chews into diseased plants and gets 

 the bacteria on its mouth parts ; then when it chews into 

 healthy plants, the bacteria gain an entrance. 



The best measures of prevention are : (i) to destroy 

 and combat the striped beetle, and (2) to burn all plants 

 as soon as they become infected. 



The various vine crops also wilt suddenly and die when 

 attacked by the grub of the stalk borer, but in this case 



