32 MASS. EXPERIMENT STATION BULLETIN 201. 



distribution of the highly concentrated nicotine product throughout the 

 mixture. 



Soap should 7iever be added when nicotine sulfate is used in this com- 

 bination. 



5. Lime-sulfur with Lead Arsenate or Calcium Arsenate. 



The great extent to which sulfur compounds have supplanted copper 

 spraj^s as fungicides has made this combination probably the most widely 

 used and most important in practice to-day. 



\Mien lead arsenate is added to lime-sulfur, a chemical reaction takes 

 place causing more or less decomposition of both materials. This reaction 

 does not decrease the fungicidal value of the mixture. In fact, Wallace 

 (46), in his investigation of apple scab control, found that the addition of 

 lead arsenate increased the fungicidal action of the lime-suKur bj^ about 

 50 per cent. The fact has long been recognized that arsenate of lead alone 

 has some value as a fungicide. 



The effect of this reaction upon the value of the combination as an 

 insecticide, however, is unfavorable. In the case of the acid lead arsenate 

 (90 per cent of that on the market to-day is of this type), the reaction with 

 lime-sulfur results in the formation of a considerable percentage of soluble 

 arsenic, with the consequent danger of severe foliage injury. The addition 

 of milk of lime, 5 pounds to 50 gallons of the mixture, checks this reaction 

 and so reduces the tendency to burn foliage (47). The arsenate of lead 

 should be added to the milk of lime, and the two thoroughly mixed together 

 and then poured into the lime-sulfur solution so that the protective agent 

 may be present when the two active ingredients are brought together. 



When calcium arsenate is used with lime-sulfur, so far as known no 

 chemical change takes place which decreases the value of the combination 

 either as an insecticide or as a fungicide. The addition of milk of lime, 

 however, as a precautionary measure seems advisable. 



6. Lime-sulfur with Lead Arsenate or Calcium Arsenate and 

 Nicotine Sulfate. 



These materials can be combined successfully and effectively. The 

 presence of nicotine sulfate is not known to modify any of the reactions 

 mentioned under 5, and the recommendations there made apply to this 

 combination also. 



The suggestions relative to the addition of nicotine sulfate to the spray, 

 and caution regarding the use of soap, apply here as in 4 above. 



