When to spray: _In the case of chewing insects_, the latter part of May
is the time to spray. The caterpillars hatch from their eggs, and
the elm leaf beetle leaves its winter quarters at that time. _In the
case of sucking insects_, the instructions will have to be more
specific, depending upon the particular insect in question. Some
sucking insects can best be handled in May or early June when their
young emerge, others can be effectively treated in the fall or
winter when the trees are dormant.

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