i6o FARM FRIENDS AND FARM FOES 



tact-killing insecticides. It is used chiefly on dormant trees 

 to kill the San Jos6 scale and other scale insects. The 

 usual formula is : Unslaked lime, 20 pounds ; sulphur, 

 IS pounds; water, 50 gallons. The lime is slaked in 10 or 

 1 5 gallons of water ; then the sulphur is added and the prep- 

 aration boiled for an hour. The rest of the water is then 

 added and the mixture is ready for use on dormant trees 

 only. 



In place of this mixture boiled by outside heat, lime-sul- 

 phur washes have lately been made by utilizing the heat of 

 the slaking lime. These are called self-boiled mixtures and 

 usually have less sulphur and lime than the formula given 

 above. They are often used for summer spraying, being 

 effective against both scale insects and various fungous 

 diseases. 



Strong soapsuds have a decided insecticide value for use 

 against plant lice and other soft-bodied insects. Whale-oil 

 soaps are more effective than ordinary soaps, and are gen- 

 erally used as insecticides. 



Pyrethrum powder commonly sold "as insect powder is 

 a standard insecticide for use against house flies and cer- 

 tain other insects. It consists of the powdered flower- 

 heads of the pyrethrum plants — a genus of composite 

 flowers which are often grown in gardens for their orna- 

 mental value. This powder is generally used dried, but 

 may be applied as a spray — by mixing one ounce of pow- 

 der with two gallons of water and letting it stand over 

 night, or by boiling for a few minutes. 



Tobacco is another contact-killing insecticide which is 

 frequently used with good results against plant lice and 

 vermin on domestic animals. The refuse stems are some- 

 times utilized in greenhouses as a mulch for growing crops 

 to prevent the development of aphides. These stems are 



