332 1' E PORT OF THE COMMISSIONER OF AGRICULTURE. 



inserted directly into the liquid, which must be kept in constant and 

 violent agitation by forcing it through some form of spray-nozzle back 

 into the same receptacle. A pump otherwise good is less adapted to 

 forming an emulsion if, instead of being inserted directly into the pail, 

 it has a large and long supply tube, in passing through which the 

 liquids are comparatively quiescent and consequently have a tendency 

 to separate. 



Another frequent cause of failure is the attempt to form an emulsion 

 by churning together a small quantity of kerosene and a large qua ntity 

 of diluent. Only a very unstable union can be effected by this means. 

 The very essence of the process requires that the oil shall be broken 

 down by driving into union with it a smaller, or at most an equal, 

 quantity of the emulsifying solution, after which, if a genuine emul- 

 sion is formed, it may be diluted ad libitum with water. 



During the past year a few cases of injury to orange trees from kero- 

 sene are reported by Mr. Hubbard, in each instance arising from the 

 use of unemulsified oil in the wash. A single case, which came under 

 his observation, will serve as an example and give emphasis to what 

 we have said in regard to the proper method of mixing the insecticide. 

 He reports as follows : 



U A grove of about one thousand trees, of all ages, had been twice 

 sprayed with the standard mixture, an emulsion containing G7 per 

 cent, of oil, diluted ten times, with beneficial results as regards infest- 

 ing insects, and without injury to any of the trees. A month or two 

 later the inside branches of about two hundred of the largest trees 

 of bearing age were given a third application, and their main trunks 

 thoroughly drenched with the liquid. A few weeks after the last ap- 

 plication four of the trees appeared to have been injured, and upon ex- 

 amination more or less of the bark was found to have been destroyed 

 at the collar of the tree. The dead bark still retained a strong odor of 

 kerosene. Two of these trees died, and two are now in process of re- 

 covery. 



"An investigation revealed the fact that at the last spraying the mix- 

 ing of the wash had been left to negro field-hands, who had dispensed 

 with the preliminary process of emulsifying the oil, and merely mixed 

 the ingredients for each 30 gallons of wash, churning the whole together 

 at one operation. The apparatus used was a large force pump affixed 

 to a barrel ami mounted on a cart. As the motion of the cart was not 

 sufficient to keep the kerosene in suspension, it separated and floated 

 on top of the liquid in the barrel. Thus the last trees sprayed before 

 mixing each fresh barrel of wash received nearly pure oil, and were 

 severely injured. 



"It should be remarked that the trunks of the trees were densely 

 shaded by low and spreading branches, which obstructed a free circu- 

 lation of air and probably greatly increased the severity of the treat- 

 ment by retarding the evaporation of the oil from the saturated sand 

 and thickened bark at the base of the trees." 



In California the attempt to use kerosene oil without emulsification 

 has been attended with disastrous results to Northern fruit trees, espe- 

 cially when crude or unrefined petroleum was used.*" This probably 

 accounts for the prejudice which has existed against the use of coal oil 

 in any form, and which has led the authorities in that State to recom- 

 uieud in preference the most heroic remedies. 



*No injury to orange trees from the application of refined kerosene in any form has 

 been reported, as far as we are aware. 



