138 STUDIES OF TREES 



How to spray: Thoroughness is the essential principle 

 in all spraying. In the case of leaf-eating insects, this 

 means covering every leaf with the poison and applying 

 it to the under side of the leaves, where the insects generally 

 feed. In the case of sucking insects, thoroughness means 

 an effort to touch every insect with the spray. It should 

 be borne in mind that the insect can be killed only 

 when hit with the chemical. The solution should be 

 well stirred, and should be applied by means of a nozzle 

 that will coat every leaf with a fine, mist-like spray. 

 Mere drenching or too prolonged an application will 

 cause the solution to run off. Special precautions should 

 be taken with contact poisons to see that the formula 

 is correct. Too strong a solution will burn the foliage 

 and tender bark. 



Spraying apparatus: There are various forms of spray- 

 ing apparatus in the market, including small knapsack 

 pumps, barrel hand-pumps, and gasolene and gas-power 

 sprayers, Figs. 97 and 98. Hose and nozzles are essential 

 accessories. One-half inch, three-ply hose of the best 

 quality is necessary to stand the heavy pressure and wear. 

 Two 50-foot lengths is the usual quantity required for 

 use with a barrel hand-pump. Each line of hose should be 

 supplied with a bamboo pole 10 feet long, having a brass 

 tube passed through it to carry the nozzle. The Vermorel 

 nozzle is the best type to use. The cost of a barrel outfit, 

 including two lines of hose, nozzles and truck, should be 

 from $30 to $40. Power sprayers cost from $150 to $300 

 or more. 



Spraying material: Ar senate of lead should be used in 

 the proportion of 4 pounds of the chemical to 50 gallons 

 of water. A brand of arsenate of lead containing at least 

 14 per cent of arsenic oxid with not more than 50 per 



