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 spraying 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: 
  Arsenate 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 oxide with not more than
    50 per cent of water should be insisted upon.  This spray may be used
    successfully against caterpillars and other leaf-eating insects in
    the spring or summer.

  Whale-oil soap should be used at the rate of 11/2 pounds of the soap
    to 1 gallon of hot water, if applied to the tree in winter.  As a
    spray in summer, use 1 pound of the soap to 5 gallons of water.  This
    treatment is useful for most sucking insects.

  Lime-sulfur wash is an excellent material to use against sucking
    insects, such as the San Jose scale and other armored scales.  The
    application of a lime-sulfur wash when put on during the dormant
    season is not likely to harm a tree and has such an excellent
    cleansing effect that the benefits to be derived in this direction
    alone are often sufficient to meet the cost of the treatment. 
    Lime-sulfur wash consists of a mixture, boiled one hour, of 40