xxxvi Remedial Measures and Insecticides. 



Kerosene. — Much diversity of opinion exists as to the use of 

 pure kerosene or a mechanical mixture of kerosene and water. 

 It is undoubtedly effective as an insecticide. 



But in too many cases it is equally fatal to plant life. Reports 

 are very conflicting. In some cases spraying with the undiluted 

 oil has been unattended by any injury to the tree, while particularly 

 successful in killing the scale. In other cases even large trees 

 have succumbed under the treatment. One cause of injury is said 

 to be the collection of oil at the base of the tree, the roots being 

 apparently nmch more sensitive to injury than the exposed parts. 

 As a precaution, earth should be banked up round the base of 

 the tree, and only sufficient oil should be used to moisten the 

 surface of the foliage and bark without any surplus to run down 

 the stem. 



Mixtures of kerosene and water have been largely employed in 

 America, and elaborate machines devised for ensuring the proper 

 mixture of the two ingredients. But under any circumstances 

 their effectiveness does not compare favourably with a properly 

 compounded emulsion. 



Referring again to one of Mr. Marlatt's reports,* I find it stated 

 that ' kerosene mixed with water is not nearly so powerful an 

 insecticide as the kerosene soap emulsion. It does not remain 

 nearly so long on the plant, and is not nearly so effective an 

 insecticide at the same strength of oil. The heavier soap or milk 

 emulsions kill more effectively, which is, perhaps, explained by the 

 heavier liquid actually bringing more oil in contact with the insect, 

 and also by its greater permanency.' Taking everything into 

 consideration, neither kerosene, nor mixtures of the oil and water, 

 can be recommended for general use — at any rate in the Tropics. 



Resin zvashes. — These are used extensively in California to 

 remove scale insects from fruit trees. The formula (taken from 

 Bulletin, No. 9 of the U.S. Department of Agriculture) is as 

 follows : — ' The summer wash usually contains twenty pounds of 

 resin, five pounds of crude caustic soda (seventy-eight per cent), or 

 three and a half pounds of the ninety-eight per cent., and two and 

 a half pints of fish oil. The winter wash contains thirty pounds of 

 resin, nine pounds of crude soda, and four and a half pints of oil. 

 The ingredients are boiled in about twenty gallons of water for two 



* Bidletin, No. 9 (New Series), U.S. Department of Agriculture (Division 

 of Entomology). 



