No. 6. DEPARTMENT OF AGRICUI^TURE. 249 



WINTER WORK AND WINTER INSECTICIDES. 



A tree free from foliage and in a dormant condition will stand 

 more severe a])plieations than can be safely applied in summer. The 

 season is longer, outdoor farm work is largely at a stand-still, the 

 insects are not breeding and, almost naturally, the fruit growers have 

 preferred to fight the scale during the winter months. 



But, while the tree is thus dormant and in its most resistant 

 state, the scale insect is in the same condition. The stage in which 

 the winter is most safel}' passed is as a half grown larva under the 

 black scale. This black scale consists of a thin Avaxy material hard- 

 ened by a lac-like substance which gives it great resisting power to 

 ordinary solvents. The first cast skin of the insect itself now forms 

 part of the covering, and brings an addition of chitiue that makes it 

 yet more resistant. The edge of the scale is sealed closely to the 

 bark of the tree or other plant, and there is no perceptible opening 

 anywhere around its margin. 



To reach the insect beneath this covering we must have either a 

 caustic that will corrode the scale or a very penetrating material 

 that will soak through or under it. 



The caustics that have approved themselves best are the lime,- salt 

 and sulphur wash on the Pacific Coast, and the whale oil soap on the 

 Atlantic Coast. The penetrating materials are crude petroleum 

 and refined petroleum or kerosene. 



Each of these will be taken up and its action and range of useful- 

 ness defined. 



LIME, SALT AND SULPHUR WASH. 



This is chemically, when properly prepared, a double sulphide of 

 lime, with an excess of lime in its composition. It is very caustic 

 and corrosive when fresh and if it remains dry holds its caustic quali- 

 ties for a considerable period of time. It decomposes slowly under 

 such circumstances, giving oil: suffocating and poisonous vapors in 

 small quantities; but acting continuously upon the insects covered 

 by it. In the presence of moisture the caustic combinations change 

 rapidly and dissolve out, leaving only a good coating of ordinary 



