74 HYDROCYANIC-ACID GAS FUMIGATION Of CALIFORNIA. 



THE PRESENCE OF OLD SCALES ON FUMIGATED TREES. 



Scales do not fall from the different pans of a tree as soon as 

 destroyed. On young and growing fruit they are easily shed, but they 

 may cling to the old fruit, leaves, and branches of trees until removed 

 by mechanical means. Dead purple scales probably cling to the 

 different pans of a tree much more generally than any of the other 

 common citrus pests. Leaves, branches, or old fruit severely infested 

 will normally remain so as long as they continue to be a pan of the 

 tree. This condition leads many growers to condemn a treatment as 

 unsuccessful because on examining a tree long after the operation 

 scales are found present. The mere presence of scales may incorrectly 

 indicate to them that they have not been destroyed. 



The prevalence with which successive generations of scale insects 

 exist simultaneously on citrus trees renders it impracticable and really 

 impossible to draw conclusions in exact percentages as to net results 

 of experimental work whenever the results fall short of eradication. 

 At the time of the treatment the scale on some leaves might all be 

 alive, while on other leaves the majority may be dead, and with all 

 gradation between to be found elsewhere. 



A DEVICE FOR COVERING FUMIGATION GENERATORS. 



During the course of this investigation much attention has been given 

 to perfecting a device for attachment to the top of the commonly used 

 open-style fumigation generator that will seiweto internipt the direct 

 rise of the hydrocyanic-acid gas. The result of these efforts, in which 

 the writer was greatly aided by Mr. Frederick Maskew. is shown in 

 figure 12. The device itself consists of a copper cover of such size as 

 to make it available for use with any of the regular-pattern generators 

 now employed by the fumigators of southern California. It is stamped 

 in a concave form from a sheet of copper, with corrugations to per- 

 mit the escape of gas. The shape is such as to conform to the size of 

 the opening of generators of different capacities and also to direct the 

 course of the escaping gas downward and distribute it uniformly 

 through the lower pan of the tent. It is attached to the generator 

 by hinges of stout copper wire secured by a key bolt passing 

 through the handle. The cover is raised by a slight pressure of the 

 thumb on a projecting piece which is curved in such a manner that 

 the cover will remain in an upright position when so required. YThen 

 the generator is emptied of its contents, the cover swings clear by its 

 own weight. A glance at the illustration will satisfy the practical 

 fumigator that it is adapted to all the requirements of rapid work in 

 the dark, while its use has demonstrated that it is simple, strong, and 

 durable. It is very possible that if the copper cover were lined with 

 a thin coverino: of lead its durability would be increased. A common 



