250 REPORT OF OFFICE OF EXPERIMENT STATIONS. 



hc'on found to v;iry (•()iisi(l('i':il)l\ in coinposition, spccilic ^Tiivity, and 

 effects upon plants when used in the form of a spi'ay. 



Kerosene eundsions have heen studied so thorou<rhly and used so 

 extensi\('ly that cxciy cntoniohjfiist understands tlieii" application. 

 Entoinolojijists, farmers, and <j:ardeners have found kerosene emulsion 

 to he \i'rv eifective in the destruction of scale insects and |)lant lice, 

 and when j^roperly prepai'ed this insecticide is practically without 

 dana-ei- to any crop. Con^iderahle difliculty has heen met with, how- 

 ever, in the use of l<(>rosene and ci'ude j)etroleum in mechanical mix- 

 tures with water. The dilKcuIty seems to lie lar<!:ely in the fact that 

 the mixtures are only of a temporary nature and not at all stable. 

 MoreoA'^er, the various spraying machines which have been con- 

 structed for the specific purpose of makinj)^ mechanical mixtures of 

 oil and water have never been ([uite satisfactory. It, ap]:)ears to be 

 impossible to obtain a mixture of water and oil containing a constant 

 proi)ortion of the oil. In fact, the variation in this respect has been 

 found to be so ii^reat that at times the machine would throw a mixture 

 containing so little oil as to be of no insecticidal value, while at other 

 times, Avithout changinc; the regulating apparatus, the percentage of 

 oil in the mixture was so great as to burn the foliage and otherwise 

 endanger the j)lants upon which the mixture was spraj^ed. Recently, 

 therefore, attention has been directed toward the correction of this 

 defect by means of a treatment which renders the oils readily miscible 

 Avith water. 



In California " it was noted that oranges were frequently spotted 

 as a result of the application of crude oil or distillation products. In 

 this State extensive experiments haA'e been carried on with so-called 

 distillates, a term which is used to refer to oils derived from crude oil 

 by a process of distillation. A considerable series of distillates are 

 obtained during the process of refining, and some of them are heavier 

 than others. In general, it Avas found at the California Station that 

 the more A^olatile oils w^ere more effective, since their vapors showed 

 a more penetrating power than the oils in the liquid form. Insects, 

 howeA^er, may be destroyed by a clogging of the breathing pores if 

 heavy and slowly drying oils are used for spra^nng. The chief 

 injury to vegetable tissue from oils Avas caused by a penetration of 

 oils into the interior of the plants. It Avas found that plants in a 

 turgid condition are less likely to absorb oil than those Avhich are 

 partly Avilted. The upper surfaces of the leaves are able to Avithstand 

 Avithout harm amounts of oil Avhich proA^e fatal when applied to the 

 lower surfaces. In some instances it Avas found that the same amount 

 of oil sprayed oAer both surfaces of the leaf may cause more damage 



o California Sta. Bui. 153. 



