i9io.] 



Hop Cultivation. 



899 



Strength of Wash. — In order that the aphis may be 

 killed by the wash, it is necessary that the strength 

 of the soap solution shall be such that, when sprayed upon the 

 bodies of the aphis or lice, it forms a thin soap-film (imper- 

 vious to air) all over their bodies and so blocks up the minute 

 " pores" or air passages of the lice, which are, in conse- 

 quence, suffocated. 



In soft water comparatively little soap is required and a 

 lather is soon obtained, but if the water is hard part of the 

 soap is used in converting the hard water into soft water, 

 and consequently much more soap is required to kill the aphis. 



When the water is exceptionally hard it is profitable to 

 soften the water with washing soda and leave it to stand for 

 half an hour before adding the soap. 



In all cases the best plan is to mix the wash so strong that 

 when a little is put into a pail and stirred up with a stick, the 

 resulting lather remains on the surface of the liquid for at 

 least five minutes. The usual strength is from 6 to 12 lb. ok 

 soap to 100 gallons of water. 



If the leaves are wet, and especially on dewy mornings,- 

 when not only the upper but also the lower sides of the leaves : 

 are wet with dew, 2 or 3 lb. of soap extra should be added,, 

 since otherwise the dew dilutes the strength of the wash and* 

 the lice escape destruction. Neglect of this precaution often 

 leads to inefficient washing. 



If mould is running upon the foliage it is a good plan to 

 add 1 lb. of liver of sulphur to each 100 gals, of this mixture of 

 soft soap and quassia ; but care should be taken to employ only 

 freshly-prepared liver of sulphur for the purpose. If exposed 

 to the air and kept a long time, or if left for some time dissolved 

 in water, the liver of sulphur is rapidly decomposed and the 

 wash not only does no good but the precipitated sulphur is 

 likely to block the nozzles. 



Force of the Spray. — Another factor of equal importance 



to the strength of the soap solution is the force with which 



the spray is applied. In order that the leaves may be well 



washed, and especially the folds in the young half-grown 



leaves where the aphides congregate, it is necessary that these 



be hit by the spray with considerable force. If the spray is 



too fine it does not penetrate into the folds of these young 



leaves and the aphides escape destruction. Many growers 



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