APPLE POWDERY MILDEW AND ITS CONTROL. 21 



PREPARATION OF CRUDE-OIL EMULSION. 



Crude-oil emulsion, ready for applying, is prepared as follows: 



Water 175 gallons. 



Fish-oil soap 10 to 12 pounds. 



Lye (caustic soda) 2 pounds. 



California crude oil 25 gallons. 



The materials are to be mixed in the spray tank in the order given 

 and with the agitator in motion. The fish-oil soap should be dis- 

 solved in hot water before adding it to the 175 gallons of water in 

 the tank, and for the first trial 10 pounds should be used. The re- 

 quired weight of lye may be added directly to the soap solution in 

 the tank, allowing a few minutes for it to dissolve before pouring 

 in the 25 gallons of crude oil. A light-brown emulsion should be 

 formed as soon as the crude oil is added, and none of the oil should 

 remain floating on the top of the mixture. Very little agitation is 

 required to keep the oil emulsified, and the mixture is ready for 

 immediate use. If the crude oil does not emulsify properly — that is, 

 if some of the oil floats on the surface or if the mixture seems to 

 contain small globules of oil — the preparation has not been successful. 

 The trouble may be due to a lack of sufficient soap, in which case 

 the remaining 2 pounds should be dissolved in hot water and poured 

 into the tank. In some cases, when very hard water is used, a little 

 extra lye may be required, and in rare cases it is necessary to use less 

 than the 2 pounds. Occasionally a little difficulty is experienced in 

 preparing the first tank of spray, but when the proportions of soap 

 and lye are once determined there will be no trouble in making the 

 emulsion. 



It will be noted that the above formula gives a 12-| per cent crude- 

 oil emulsion. Such a mixture must be used only when the trees are 

 entirely dormant, preferably during January. The spraying should 

 be very thoroughly done, so as to produce a uniform, shiny, dark- 

 brown coating over the entire surface of the twigs and branches. 

 It may be well to repeat the statement that this winter spraying 

 with crude-oil emulsion is not for the direct purpose of controlling 

 the mildew, but is intended as a stimulant which will induce the 

 production of vigorous early foliage, and this latter is of decided 

 importance in mildew control. 



Investigations that are still in progress seem to indicate that 

 under some conditions dormant spraying with solutions of nitrate of 

 soda plus caustic soda will be more desirable than crude-oil spraying. 1 



1 Ballard, W. S., and Volck, W. H. Winter spraying with solutions of nitrate of soda. 

 Journal of Agricultural Research, v. 1, na. 5, p. 437-444, pi. 50-51. 1914. 



