METHODS OF CONTROL 201 



system. Observations show that nema- 

 tode injury is confined to the upper roots 

 of the plant, that is, those which are 12 to 

 16 inches deep. Hence, if the roots are 

 induced to penetrate deeper in the soil, 

 part of the injurious effect will be over- 

 come. Potassium salts have been found 

 to be beneficial, especially in soils poor in 

 potash. It has been found in Germany 

 that the sugar beet nematode removes 

 equally all mineral salts from the roots. 

 Therefore to improve such a condition we 

 would need to add only that mineral which 

 was originally lacking. This may explain 

 the effect of potash in combating this dis- 

 ease. 



Control of Soil-Infesting Insects. 

 Spraying the soil will be of little value in 

 the control of underground insect pests. 

 Where wire worms are causing injury to 



