76 INSECTICIDES FOR SUCKING INSECTS 



tions range from 1 part to 500 in the case of resistant insects down 

 to 1 part to 1000 in the case of tender plant Hce. The dilutions for 

 killing lice and mites on animals are similar to the last named. The 

 strength of 1 to 500 should be used only as a wash and not as a dip, 

 when treating pests on animals. 



'' Sulphate of Nicotine " is a preparation of similar strength, and 

 the dilutions are the same. 



Liquid " Nico-Fume " contains 40 per cent free nicotine, but the 

 dilutions and manner of use are similar to the above. 



" Black Leaf Extract " contains a much lower percentage of nico- 

 tine, and less water is added to it than to the others named. 



Home-made Tobacco Extract 



If tobacco stems or tobacco dust are available, an extract may be 

 made at home. To prepare, pack the stems in a pail or kettle and 

 cover with water. Allow to stand over night. Or, boil 1 pound of 

 dust or stems in 1 gallon of water. An hour's boiling is sufficient. 

 Dilute the extract with 1 to 2 parts of water. This material 

 may safely be applied to plants in leaf and is effective against plant 

 lice. Add soap at the rate of 1 pound to 50 gallons of spray. It is 

 not advisable to employ this as a winter spray to kill the eggs of plant 

 lice because the percentage of nicotine present may not be sufficient. 



Insect Powder 



Insect powder 1 ounce 



Water 2 gallons 



This is the material variously known as pyrethrum, buhach, or 

 Persian insect powder. It consists of the finely ground flower buds 

 of a plant. The active principle is volatile ; hence the material rapidly 

 loses its strength on exposure to air. It must be fresh, or must have 

 been kept in a closed receptacle, to be effective. 



Commonly it is used dry. Small powder guns are obtainable for 

 applying it. 



To use it as a spray, mix 1 ounce in 2 gallons of water. If it is 



