200 



WEEDS AND PLANT DISEASES 



kinds can you name? What is the most troublesome 

 weed in the vicinity in which you live ? 



Plant diseases. Cultivated plants are subject to 

 many diseases, nearly all of which are due to bacteria 

 or fungi. Wheat rust is a disease caused by fungi that 



live on the wheat and pene- 

 trate into the living tissues of 

 the plant. The rust particles 

 are the spores of the fungi. 

 Pear blight is due to bacteria 

 in the sap of the tree. The 

 farmer must do many things 

 to keep his plants healthy. 

 Some of the smuts on grain 

 may be prevented by treating 

 the seeds with chemicals that 

 destroy the spores of the fungi 

 that cause the smuts. When 

 fungi grow on leaves or fruit, 

 as in the case of leaf blights 

 and the apple scab, spraying 

 with chemicals will kill the fungous growth. When 

 the disease is due to bacteria in the sap, like pear or 

 apple blight or the bacterial disease of squash vines, 

 the only thing that can be done is to destroy the 

 diseased plants, in order to prevent the spread of the 

 disease. 



One of the best ways of controlling plant diseases 

 is breeding for the production of disease resistance. 



SMUT ON OATS 



