CHAP. XI.] THE CONTROL OF IXSKt 1 PESTS OF < ROPS. 105 



Repellents. 



Besides insecticides, which actually kill the insects against 

 which thej arc used, it is often useful to employ substances which 

 act as repellents; thai is to say, thej drive insects away and 

 keep them from attacking the plants or areas so treated. Although 

 the action of repellents is necessarily only temporary it is 

 important to gh e plants, and particularly young plants, an opportu- 

 i a critical period, such as transplantation, and it 

 is under such circumstances that repellents may be used. 



Bordeaux Mixture, though more often used as a fungicide, 

 makes the parts of plants sprayed with it temporarily distasteful 

 to insects, it is made bj dissolving one pound oi Copper Sulphate 

 (blue stone) and one pound of quicklime separately in water, mixing 

 the two cold solutions graduallj in a third vessel and diluting to 

 tin gallons for use. The mixture must be well strained. It should 

 In tested lor any excess of copper bj dipping in a knife-blade ; 

 if this acquires a brown deposit of copper, more lime must be 

 added until the excess is all neutralized ; the final mixture should 

 be as nearly neutral as possible, without excess of either lime or 

 copper. The Copper Sulphate should not be dissolved in a tin or 

 iron vessel, but vessels of wood, copper, glass or stoneware are all 

 suitable. 



Dry Slaked J. inn-, dusted onto and around plants, especially 

 vegetables, sometimes drives awa\ insect pests. It may be 

 prepared by placing a little quicklime in a metal vessel and pour- 

 ing on hot water ; the lime will slake and crumble to a verj tine 

 powder. Flowers of Sulphur may be added to the lime when this 

 is dusted onto plants. 



Calcium Carbide Residue, as removed from Acetylem 

 generators, may also be used for protecting vegetables, mixed with 

 earth or sand in the proportion of one in five, or one in ten in the 



i] j oung plants. 



Tobaa »tems or leaves chopped up fine, may 



also be dusted onto leaves as a repellent, but is more valuable 

 when placed in a small ring around the stems of plants attacked by 

 root-borers or subterranean Aphids oi : the top layer of 



soil being removed and afterwards replaced. 



Such insecticides as crude oil emulsion, soap, and phenyle, 

 when added to the irrigation water at a strength insufficient to kill 

 insect-pests, sometime- act a- repellents to drive them awaj 

 temporarily. 



Copper Sulphate Solution i- used < specially for the clipping of 

 cane sctt> before planting to keep away termites until the young 



