378 INSECTS AFFECTING VEGETATION 



They have the disadvantage of costing a good deal more than the 

 standard emulsions or the lime-sulphur wash but have the great 

 advantage of being always ready for immediate use without trouble- 

 some preparation. They can not be diluted for winter applications 

 against scale insects with more than 10 or 15 parts of water to give 

 good results, and there is some danger of injury to the trees if they 

 are carelessly or excessively applied. They have, however, a very use- 

 ful place, and especially as furnishing a good insecticide where only 

 a few trees are to be treated and the owner would probably not go to 

 the trouble of preparing an emulsion or the lime-sulphur wash. They 

 have been so far principally used against the San Jose scale as dor- 

 mant tree washes. 



The Resin Wash. The resin wash has proved of greatest value 

 in California, particularly against the red scale and the black scale 

 on citrus plants, and the last named and the San Jose scale on 

 deciduous plants, and will be of use in all similar climates where 

 the occurrence of comparatively rainless seasons insures the con- 

 tinuance of the wash on the trees for a considerable period, and 

 where, owing to the warmth, the multiplication of the scale insects 

 continues almost without interruption throughout the year. Where 

 rain are liable to occur at short intervals, and in the Northern States, 

 the quicker acting and stronger kerosene washes and heavy soap ap- 

 plications are preferable. The resin wash acts by contact, having a 

 certain caustic effect, but principally by forming an impervious, 

 smothering coating over the scale insects. The application may be 

 more liberal than with the kerosene washes, the object being to wet 

 the bark thoroughly. The wash may be made as follows: 



Resin pounds . . 20 



Crude caustic soda (78 per cent) do. ... 5 



Fish oil pints. . 2% 



Water to make gallons. . 100 



Ordinary commercial resin is used, and the caustic soda is that 

 put up for soap establishments, in large 200-pound drums. Smaller 

 quantities may be obtained at soap factories, or the granulated caus- 

 tic soda (98 per cent) may be used 3% pounds of the latter being 

 the equivalent of 5 pounds of the crude. Place these substances, 

 with the oil, in a kettle with water to cover them to a depth of 3 or 

 4 inches. Boil about two hours, making occasional additions of 

 water, or until the compound resembles very strong black coffee. 

 Dilute to one-third the final bulk with hot water, or with cold water 

 added slowly over the fire, making a stock mixture, to be diluted to 

 the full amount as used. When sprayed the mixture should be per- 

 fectly fluid, without sediment, and should any appear in the stock 

 mixture reheating should be resorted to; in fact the wash is pref- 

 erably applied hot. 



As a winter wash for scale insects, and particularly for the more 

 resistant San Jose scale, stronger washes are necessary. In southern 

 California, for this insect, a dilution one-third less, or water to make 

 662/3 gallons instead of 100 (see formula), has given good results. 



