16 MISSOURI AGRICULTURAL EXPERIMENT STATION BULLETIN 177 



As the table shows in 1920 potassium cyanide was used twice as strong 

 as is recommended. Also sodium cyanide (NaCn) was used. Sodium cyanide, 

 which is stronger than potassium cyanide and which is ordinarily used at 

 the strength of one ounce sodium syanide, one and one-half ounces sul- 

 phuric acid and three ounces water. Every treatment of cyanide used in 

 1920 killed 100 per cent of the scale. As to the effect of the treatments upon 

 the trees the HCN used at the rate of 1-1-3 it seems causd less injury both 

 upon wet and dry trees. 



Effect of hydrocyanic-acid gas upon scale on peaches* Somewhat bet- 

 ter results were obtained on peaches. From counts made on May 25, as is 

 shown by the table, three of the treatments gave perfect results so far as 

 controlling the scale was concerned. 



TABLE 4. PEACHES TREATED IN 1916 



Hydrocyanic-acid gas used at the rate of 1/2-1/2-1% on damp trees gave 

 the poorest results. A larger number of the trees treated dry were dead 

 May 26 than was the case with those treated wet. 



TABLE 5. PEACHES TREATED IN 1917 



In 1917 hydrocyanic-acid gas proved to be effective in killing the scale 

 on peaches upon both wet and dry trees. Fifty per cent of the scale on 

 the check trees had passed the winter in safety. 



