PLANT DISEASES. ^9 



hibernating weevils leave their winter quarters and feed on the 

 swelling buds, after which they again seek cover prior to egg- 

 laying, which takes places about a fortnight later. At their 

 first appearance they are practically insensible to jarring, but 

 are easily shaken off when egg laying, (c) That very many, if 

 not all, seek their winter quarters in the bark crevices of apples, 

 plums and other trees, and that in this position it is possible 

 to kill them by a cheap spray. 



Insecticidal Washes. — The work done during the past nine 

 years may be grouped under three heads (i) cover washes, 

 (2) The importance of wetting power, (3) combined insecticides. 

 Experiments on cover washes, of which the main ingredient was 

 whiting or lime, have shown that lime is the more satisfactory, 

 and further that with the exception of glue, every addition of 

 another body, including salt as commonly advocated, impaired 

 the good qualities of the mixture. The method of slaking lime 

 was shown to have the greatest bearing on the resulting adhesive- 

 ness of the wash and that, contrary to general opinion, a cold 

 lime wash was superior to hot. The best conditions for 

 slaking have been determined, as well as the range of time during 

 which lime spraying is effective and safe. The way in which 

 lime spraying controls certain insects has been shown to be due, 

 not to any direct chemical action, but simply to the mechanical 

 cover. 



Eight years ago, the importance of the wetting power of 

 summer v/ashes was pointed out, and since that time work has been 

 done on various well-known accessory wetting substances such 

 as casein, gelatine, saponin soap and paraffin oil emulsions, which 

 has shown that the first three are almost valueless for the 

 purposes of wetting insects. The usefulness of soap was of 

 course well known, but the possibilities of paraffin oil emulsions 

 were much less so. Investigation showed that a very high degree 

 of wetting power could be obtained by suitable combinations 

 of oil and soap. The reason of the injurious action found to 

 follow the use of some formulas has been shown to be due to 

 a too high proportion of paraffin to soap, and all the possible 

 economic mixtures, their wetting powers and liability to injury, 

 have been tabulated. This work led to the use of a 2 per cent, 

 emulsion which, combined with nicotine, has proved of the 

 greatest use as a summer treatment for Woolly Aphis. It wets 

 with great ease, has a strong killing action, and is non-injurious 

 to green foliage. This mixture has a dual action in that it is 

 effective both on sucking insects and on many biting ones, 

 such as caterpillars in their young stages. It thus forms an 



