70 Diseases of Truck Crops 



common to crops, but they too excrete certain poisons 

 into the soU which become harmful to the crop in 

 the company of which they grow. Moreover, weeds 

 rob the soil of vast quantities of water which other- 

 wise would be utilized by crops. This is an important 

 consideration where irrigation is not practiced ex- 

 tensively and in the more arid regions. 



