216 SHADE-TREES IN TOWNS AND CITIES 



tached to the hose, the spray mixture passes through the 

 tube and out of the nozzle at the other end. 



Precautions in Spraying. — Spraying is one of the most 

 important and expensive operations in the care of trees. 

 To be at all effective it must be very carefully done and ca'n- 

 not be left to ignorant hands. There must be thoroughness 

 in all applications made. The man at the nozzle must know- 

 precisely what he is aiming at and how he expects to accom- 

 plish his aim. With the best appliances and proper insecti- 

 cides, failures frequently result if the work is not carefully 

 done. 



When applying stomach poisons, the spray should not be 

 continued until the foliage drips too freely, for the effective- 

 ness of the fine mist will then be destroyed. All the glob- 

 ules on the leaf will unite to form a film which will run off 

 and leave little of the poison adhering to it. After a fine 

 mist dries on the leaves, they can be sprayed again and will 

 then hold more poison than would have been possible to 

 apply during one operation. 



The application of contact insecticides, however, should 

 be more thorough than that of stomach poisons and contin- 

 ued until the leaves drip. These poisons act only until they 

 dry, and if any insect is not touched it will escape. Stomach 

 poisons adhere to the leaf -tissue, and the chewing insect is 

 bound to get some of the poison if it continues to feed long 

 enough— if not on one part of the leaf then on another. 



All spraying mixtures should be carefully strained before 

 being poured into the insecticide tank. This precaution will 

 prevent the clogging of the nozzle. 



A warm, sunshiny, calm day is ideal for spraying. When 

 there is no wind there is little waste of spraying material 

 and the insecticide adheres more firmly to the leaves and 



