158 IVceds. 



entirely killed by the spray and the roots 

 and stems may contain sufficient vitality 

 to mature the seeds, even after the leaves 

 are killed. The proper time to apply the 

 spray of course varies with the locality, but 

 it is usually in May or early June. The 

 most effective work can be done if the 

 spray is applied in damp, cloudy weather, 

 or toward evening, when the evaporation 

 will not be rapid. Naturally, the work 

 should not be done when a rain is immi- 

 nent, as the rain will wash the chemical 

 off the leaves and destroy its effectiveness. 

 Weeds are more easily killed when the 

 growth is rapid than when it is slow. 

 Usually one spraying is sufficient, but if 

 the weeds are numerous, an additional 

 application a week or ten days later may 

 be necessary. 



The materials used in spraying are usu- 

 ally solutions of iron sulfate, copper sul- 

 fate, or common salt. Iron sulfate (cop- 

 peras) is generally considered to be the 

 most effective chemical for use in destroy- 

 ing mustard and similar weeds. About 50 

 to 55 gallons of any of these solutions are 

 required to cover the weeds on an acre of 

 land properly. The proper strength of the 



