2 HYDROCYAXIC-ACID GAS FUMIGATION IX CALIF ORNIA. 



lottesville. Va. The same year it was first used in the treatment of 

 nursery stock, and its development along this line has been so great 

 and important that to-day in many States the fumigation of decidu- 

 ous stock before it is planted is required by law. The use of hydro- 

 cyanic-acid gas against insects affecting greenhouse plants has been 

 successfully carried on for a number of years. Among the other 

 important uses to which this gas has been successfully put are the 

 treatment of mills, various other buildings, and stored products 

 infested with insects. The ease with which this gas may be generated 

 as well as its destructive power, greater than that of any other known 

 insecticide, leads the writer to believe that as soon as the various 

 uses to which this gas may be put have been thoroughly investigated 

 and placed on a stable basis the future development of hydrocyanic- 

 acid-gas fumigation will be quite as important and extensive as has 

 been its past development. 



RECENT RENEWAL OF INTEREST IN FUMIGATION IN 



CALIFORNIA. 



The hydrocyanic-acid-gas treatment of citrus trees continued to 

 become more widely used and to hold general favor with the fruit 

 growers of southern California until about 1901. when the distillate 

 spray was introduced. The treatment of trees with distillate was 

 much cheaper than with hydrocyanic-acid gas. This fact, together 

 with the fact that the distillate treatment was indorsed by many of 

 the more prominent horticultural authorities and fruit growers led to 

 its widespread use during the next few years. Simultaneously the 

 introduction from South Africa of Scutdlista cyanea Motschulsky, the 

 parasite of the black scale (Salssetia olese Bern.\ and its subsequent 

 splendid showing led many people to abandon treating their orchards 

 in the hope that this beneficial insect would hold the black scale in 

 check. 



By 1903-1905 it had become very evident that the distiUate spray 

 had not only failed to keep the scales under control, but that its con- 

 tinued use in many cases produced an injurious effect upon the tree 

 itself. The Scutellista also had failed to control the black scale, 

 although even a conservative must admit that its work has been of 

 a most praiseworthy type. Spraying rapidly sank into disuse during 

 1905 and 1906. until at the present time it has almost entirely given 

 way to fumigation. The experience of the prominent fruit growers 

 with the distillate spray has thoroughly satisfied them of the great 

 superiority of the hydrocyanic-acid-gas treatment to that with a 

 spray for scale insects on citrus trees. 



In the winter of 1903-4. Dr. G. Harold Powell, then of the Bureau of 

 Plant Industry. United States Department of Agriculture, com- 

 menced an investigation of the decay of oranges while in transit 



