PLANTING AND CARE OF TREES 175 



Contact Insecticides — Insects that obtain their food by piercing 

 the epidermis and sucking the juices from the plant tissue, must 

 be killed by contact and the preparations used for the purpose 

 are called contact insecticides. Such preparations are usually 

 caustic in character and kill by irritation or by clogging the 

 breathing pores of the insect. 



Common hard soap at the rate of one pound to six gallons of 

 water, is commonly used for plant lice. Whale-oil soap which 

 comes in paste form, is usually preferred for this purpose and is 

 used in the proportion of one pound to five gallons of water. It 

 is also used to some extent as a dormant spray for scale insects. 

 For this purpose it is used in the following proportion : 



Whale-oil soap 2 pounds 



AVater 1 gallon 



Either kind of soap is more easily dissolved in hot water. 



This preparation is too expensive to be used where there are 

 many trees to be sprayed, but when only one or two trees or a 

 few bushes are affected with scale insects, it is a convenient remedy 

 and is not so disagreeable to apply as some of the other prepara- 

 tions. 



Kerosene emulsion is probably the best remedy for the control 

 of sucking-insects when the spraying must be done while the tree is 

 in foliage. A stock solution may be made up and used when 

 required and at any strength: 



Kerosene 2 gallons 



Hard soap }^ pound 



Hot water 1 gallon 



Cut the soap into thin slices, dissolve in the hot water, remove 

 from the fire and pour it into the kerosene while hot. Churn 

 thoroughly, or pump into itself with a force pump, until a creamy 

 emulsion is formed, which will mix readily with cold water. For 

 use on foliage, dilute at the rate of one to twelve. Some plants 

 with tender foliage require a weaker solution. For use on dormant 

 trees, dilute at the rate of one to three. 



Tobacco decoction, made by steeping one pound of tobacco stems 

 or waste in two gallons of water, is a safe remedy for plant lice 

 on tender-foliaged plants. 



