Relation to Deleterious Chemical Agents 459 



(3) When it is desired to suppress weeds or to prevent 

 weed seeding during the maturity of a seed crop. 





FIG. 134. Lawn with dandelions, similar to that in Fig. 133, but treated 

 with iron sulfate two weeks before blossoming. [Photograph by H. L. 

 Bolley.] 



(4) When, during the growing season of the crop, a ma- 

 jority of the undesirable weeds are more sensitive than the 

 crop grown. 



