INSECTICIDES, FUNGICIDES, ETC. 147 



already been mentioned, and these may be sprayed on to the 

 trees in the form of a 3 or 4 per cent, admixture with water or 

 dilute paraffin oil emulsion (p. 152). If a decoction is used it 

 should not be boiled, 



Quassia with soft soap is much used for destroying aphis. 

 The wash is made by boiling J to 3 Ibs. of chips of the wood with 

 10 gallons of water, and adding J to 3 Ibs. of soft soap. 



Nicotine appears to be by far the most effective of the vegetable 

 insecticides. A decoction of " denatured " tobacco which 

 contains about 70 per cent, of tobacco mixed with sulphur, 

 asafcetida and flour may be used, but owing to the great 

 variation in the nicotine-contents of tobacco, it is better to use 

 nicotine itself. The results obtained at Woburn (pp. 223, 224) 

 show that a solution of 0-075 per cent, is very effective for 

 aphis, apple psylla, etc. : it is well to add to the solution 0-5 per 

 cent . of soft soap. 



It is noticeable that various alkaloids, such as aconite, hyos- 

 cyamine, nux vomica, etc., which are highly poisonous to verte- 

 brate animals, have but little action on insects (p. 226). 



(2) Soap is generally used in connection with other substances, 

 as in the instances just mentioned, but it is also used effectively 

 alone for killing certain aphides, such as those attacking roses. 

 It is probable that its action in such cases is due to its clogging 

 the breathing apparatus of the insect : its low surface tension 

 also enables it to wet bodies more effectively than other spray- 

 fluids, though, it may be remarked, a similar action in the case 

 of saponin does not appear to increase the effectiveness of sub- 

 stances to which it is added (p. 195). Soap is also largely used as 

 an agent for emulsifying paraffin oil. In connection with this, 

 and especially if alkali is added as well, it is used for the destruc- 

 tion of insect eggs, although its chief function under such 

 circumstances is that of a detergent (pp. 107, 202). 



(3) Sulphur is generally used in the solid condition, as men- 

 tioned above, although it occasionally is made into a liquid wash 

 with water and other substances. As an insecticide, and still 

 more as a fungicide, the sulphides play an important part. The 

 origin of their use seems to have been the application to trees 

 of a liquid used as a sheep dip, and known as the lime -sulphur-salt 

 wash (California wash) or the lime-sulphur-soda-salt wash (Oregon 

 wash). There are many recipes for making these, the more 

 usual being to boil together for 45 minutes 3 to 6 Ibs. of quick- 

 lime with 3 Ibs. of sulphur, 3 Ibs. of salt, and a limited quantity 

 of water, the resulting liquid being afterwards diluted to ten 



