THE WAR ON INSECTS 289 



bark scales, and against such mites as hibernate under 

 bud scales or in similar positions. They are not espe- 

 cially effective against insect eggs, and have little 

 fungicidal value. In all cases where the oils and the 

 lime and sulphur are equally effective, the latter is 

 preferable because of its influence on plant diseases. 

 "Soluble" oils are not safe as summer washes at effec- 

 tive strengths, although when carefully applied on 

 mature foliage of hardy trees, no serious injury is caused. 



Miscible oils can be made at home and formulas 

 have been published minutely describing the process; 

 but it requires skill, absolutely uniform materials and 

 an outfit that only the user of large quantities can 

 afford. Furthermore it is an unpleasant and even 

 somewhat dangerous process which can hardly be 

 recommended to ordinary farmers and fruit-growers, 

 and certainly not to gardeners using only a few gallons 

 or even barrels. 



There is another field for kerosene emulsion and the 

 hke when it is necessary to reach certain leaf-miners 

 which, while feeding on plant tissue are never exposed 

 to the action of arsenical coverings, but live entirely in 

 the leaf tissue. There is usually, however, an opening 

 to the surface, or the tissue above the mine is so thin 

 as to be readily penetrated by the oil; hence a contact 

 insecticide against a leaf-miner is indicated. 



It is with the mineral oils as with the lime and 

 sulphur; the effects are not equally satisfactory under 

 all climatic conditions. Applications that are entirely 

 safe in one locality may be distinctly injurious to plants 

 in another, and a little caution must be observed when 

 the material is used for the first time in localities differ- 

 ing from those in which it has been tested. 



Another combination with both caustic and pene- 

 trating qualities as well as a specific feature of its own 

 19 



