FIGHTING INSECT PESTS 



185 



If, however, the insect pest is one with sucking mouth- 

 parts, obtaining its liquid food underneath the covering 

 tissue of leaf, fruit or twigs— all plant-lice, scale insects, 

 squash bugs, stink bugs and sucking bugs generally are of 

 this category — the poisonous spray must be one that will 

 kill by contact. It must be what is called an external 

 irritant. The most available and effective of these external 

 irritants is kerosene. As, however, the raw oil is also very 

 irritating and dangerous to plant tissue as well as to insects 

 it must be made into an emulsion 

 before being sprayed on to the insect- 

 infested foliage. The emulsion may 

 be made as follows: Dissolve one- 

 half pound of hard soap shaved finely 

 in one gallon of boiling water. Add 

 this to two gallons of kerosene aud 

 churn the mixture with a force pump 

 for a few minutes until it becomes 

 a soft butter -like mass. This stock 

 emulsion should be mixed with water 

 whenever it is desired to make up the 

 spray, in the proportion of one part of stock to ten parts of 

 water. 



Other insecticides that kill by contact are mixtures of 

 whale oil soap and water in the proportion of about one 

 pound of whale oil to six gallons of water; also pyrethrum 

 powder and water in the proportion of one pound of powder 

 to thirty gallons of water. 



For scale insects, which are so covered and protected by 

 their waxen shell as to be very difficult to kill by contact, 

 washes made of unslacked lime 50 lbs., sulphur 25 lbs., salt 

 18 lbs., and water sufficient to make 100 gallons; or resin 

 20 lbs., caustic soda (70% strength) 5 lbs., fish oil 3 lbs., and 

 water sufficient to make 100 gallons, may be used. 



Lime alone is a very good insecticide; the best way to 



Fig. 91. A San Jose 

 scale insect underneath 

 its waxen covering. 

 (Much enlarged.) 



