86 HYDROCYANIC-ACID GAS FUMIGATION IX CALIFORNIA. 



FIELD TESTS. 



In August. 1909, H acres of orange trees at Whittier, Cal.. severely 

 infested with the purple scale (LepidosapJies beclcii Newm.), which 

 was largely in the egg stage — the most difficult one in which to 

 destroy it — were fumigated with a 124 per cent sodium cyanid, using 

 the 1—1 J— 2 formula. The length of exposure was one hour. Three 

 strengths of gas were used, calculated from the cyanogen present in 

 the cyanid as equivalent to 1, 1J, and H, of the strength of regular 

 schedule Xo. 1 of potassium cyanid, as given in this Bulletin. The 

 -writer says strengths equivalent to these different schedules of potas- 

 sium, because it is known from previous discussion that an ounce of 

 high-grade sodium cyanid will produce considerably more gas than an 

 ounce of high-grade potassium cyanid owing to its higher cyanogen 

 content. In the 124 per cent sodium cyanid the advantage in favor 

 of that product is practically one-fourth. It follows that if a high- 

 grade sodium cyanid is used with dosages of the same size as three- 

 fourths of schedule No. 1 of potassium cyanid practically the same 

 strength of gas will be given off as with potassium cyanid at the 

 dosages of full schedule Xo. 1 of potassium cyanid. 



In examining the results where the equivalent of schedule Xo. 1 of 

 potassium cyanid was used, only 4 hve insects, 2 with healthy eggs, 

 were found, these being distributed between 3 different trees. Xo 

 live insects or eggs were found on the trees treated with dosages 

 equivalent to 1^ and H of schedule Xo. 1 of potassium cyanid. 



Experiments against the purple scale where potassium cyanid was 

 used have shown that it required a 1J schedule of that chemical to 

 produce practically the same results as have been secured in this 

 experiment with sodium cyanid at a strength equivalent to Xo. 1 

 schedule of the potassium cyanid. With this high-grade sodium com- 

 pound the equivalent of a 1^ schedule of potassium cyanid eradicates 

 the purple scale, whereas with potassium a 1+ schedule has been 

 required to accomplish this result. Hence this field experiment 

 would indicate that under the crude conditions of orchard work 

 sodium cyanid produces not only as good a generation as the potas- 

 sium but a decidedly superior one. 



In a second experiment an acre of orange trees very severely 

 infested with purple scale was fumigated, partly with a high-grade 

 sodium cyanid and partly with the regular potassium cyanid. The 

 tents used were of a new character of material of very tight texture. 

 The sodium cyanid produced exactly as satisfactory results in this 

 experiment as the potassium cyanid. 



During Xovember, 1909, a 4-acre block of orange and lemon trees 

 severely infested with the purple scale was fumigated with sodium 

 cyanid by an outfit of the Whittier Citrus Association, using the 





