SCALE INSECTS OF IMPORTANCE 339 



35° was almost uniformly fatal. A safe petroleum, he states, must be 

 either a green or an amber colored paraffin oil, not an asphaltum oil. 

 There is still need of more experiments along this line and of a clearer 

 understanding of just what is meant by crude oil before the use of undi- 

 luted petroleum can be advised in this state. 



Kerosene. Spraying trees in early spring with ordinary undiluted 

 kerosene did not result in nearly so thorough work as a 20% crude 

 petroleum emulsion, and it was much more injurious to the trees. Its 

 use can not be advised. 



Kerosene emulsion. A mechanical 10% kerosene emulsion is a 

 most excellent summer spray to be applied when the young scale insects 

 are numerous, and it has proved harmless to the trees. H. P. Gould has 

 used a 20% mechanical emulsion in summer without harming the trees 

 to an appreciable extent, but as the lower percent of oil gives very satisfac- 

 tory results, there is no necessity of using more. Early June appli- 

 cations would probably prove very effective against appletree and scurfy 

 bark lice. The 20% and 25% mechanical emulsions applied in early 

 spring just before the buds started, failed to kill many scale insects, and 

 its use is not recommended at this time. 



Other summer sprays. The ordinary kerosene emulsion may be 

 prepared by taking i^ pounds of hard soap, i gallon of boiling water 

 and 2 gallons of kerosene. Dissolve the soap in the water, add the 

 kerosene and then agitate the mixture vigorously by stirring or by repeat- 

 edly passing it through a force pump with a nozzle attached, till an 

 emulsion of creamy consistency is obtained, and oil does not rise to the 

 surface. For summer work against the San Jose scale this may be 

 diluted with 9 parts of water, i pound of whale oil soap dissolved in 

 5 gallons of water may be used in a similar manner without injury to the 

 trees. The sour milk emulsion, which is simply 2 gallons of kerosene and 

 I gallon of sour milk, emulsified and diluted as described above, is pref- 

 erable for limestone regions or where soft water can not be obtained 

 readily. These summer sprays are of service only in checking the San 

 Jose scale, if previous applications have for some reason proven unsatis- 

 factory. They are very efficient when used against appletree and scurfy 

 bark lice. 



Fumigation in orchards. Treatment of pernicious, or San Jos^ 

 scale with hydrocyanic acid gas gave most excellent results on small 

 trees in an orchard. Unfortunately it involves the use of costly tents, 

 specially for large trees. It is admirably adapted for large orchards of 



