used it was not efficient enough to warrant its application on a 

 commercial scale. 



Salt. The injurious effect of salt upon vegetation is a mat- 

 ter of common knowledge. Plants show some variation in their 

 resisting power to salt, but a maximum salt content is soon 

 reached in the moisture of the soil, after which the plants die or 

 can not thrive. Salt has been applied for killing weeds, either 

 dissolved in water or sprinkled upon the ground about the weeds 

 to be destroyed. Salt is chiefly valuable for this purpose in side- 

 walks or roadsides where it is not desired to grow cultivated crops 

 after the weeds are destroyed. In such places there is no harm 

 from the presence of large quantities of salt in the soil. As a 

 spray it has been found that salt applied at the rate of 80 bar- 

 rels is inefficient for the destruction of field weeds. It is, there- 

 fore, scarcely to be recommended in the list of commercial weed 

 destroyers in field practice. 



Sulphuric acid. On account of its great oxidizing and burn- 

 ing power, sulphuric acid has frequently been thought of as a 

 weed destroyer. When used in a 15 per cent solution in water, 

 Wilson 1 found sulphuric acid to be very efficient for destroying 

 weeds but rather too expensive. Similar results have been ob- 

 tained in Maine and elsewhere. Sulphuric acid is objectionable 

 on account of the danger connected with its use by ordinary la- 

 borers, and its destructive effect on spraying apparatus. At the 

 Station sulphuric acid was tried as a means of destroying guava, 

 but without satisfactory results. 



Copper sulphate. Copper, both in the form of sulphate and 

 nitrate, but particularly the former, has been widely used in 

 killing various kinds of weeds, especially wild mustard. The 

 effectiveness of copper sulphate for this purpose has been thor- 

 oughly demonstrated, both in Europe and the United States. 

 A 3 to 5 per cent solution is commonly recommended to be 

 applied as a spray. Hitier 2 had excellent results in destroying 

 wild mustard from spraying with a 4 per cent solution of copper 



1 Minn. Sta. Bui. 95. 



2 Jour. Agr. Prat. 5 (1905) pp. 65-8. 



