RUST OF ANTIRRHINUM. 



55 



Table 7. — Toxicity of Copper Sulfate Spray to the Foliage of Snapdragon. 



Per Cent Copper. 



Injury to Foliage. 



0.25, 

 0.125, 

 0.0625, 

 0.0312. 



t 



Markedly injured. 

 Markedly injured. 

 Slightly injured. 

 \o injury. 



It is evident from this that a copper sulfate sokitioii which will prevent 

 germination of urediniospores, a solution which must contain at least 

 0.25 per cent copper, is toxic to the foliage of the host. Copper sulfate 

 therefore cannot be used as a control for snapdragon rust. 



Cuprammonium sulfate (Eau celeste), CuS04.4NH3.H..)0, was the 

 next fungicide tested. On drying, this gives rise to basic copper sul- 

 fate which on further weathering passes to copper sulfate. In these 

 toxicity tests it was used in strengths of solution containing from 0.008 

 per cent to 0.5 per cent copper sulfate, with results shown in Table 8. 



Table 8. — Effect of Various Strengths of Cuprammonium Sulfate on the 

 Germination of Urediniospores of P. Antirrhini. 



As here shown, a solution of cuprammonium sulfate containing 0.065 

 per cent copper prevents germination of urediniospores of P. Antirrhini. 



The toxicity of this solution to the foliage of snapdragon was tested 

 as in the case of copper sulfate. Solutions containing 0.25 or 0.125 

 per cent copper injured the foliage markedly, and a solution containing 

 0.065 per cent copper produced some injury. Cuprammonium sulfate 

 at the strength toxic to the fungus is injurious to the host plant, and 

 cannot therefore be used. 



Other copper salts were not tested, for Melhus (loc. cit.) has found 

 cupric sulfate (CuSO4.5H.2O), cupric nitrate (Cu(NO:!)2-3H..,0), cupric 

 acetate (Cu(C..,HoO..')2-H,,0) and cupric chloride (CuCl.,.2H.O) to be 

 about equally to.xic if they contain the same amounts of the toxic principle, 

 — copper. 



