Insects of Shade Trees and Their Control. 11 
the bark. Suffice it to say here that such treatments are entirely 
without merit in controlling insects and often are decidedly injurious 
to the trees treated. 
THE STOMACH-POISON SPRAYS. 
' 
The standard poisons used at present for killing chewing insects 
are arsenate of lead and arsenate of lime (calcium arsenate). Both 
are procurable in the market, usually in seed stores, and come in 
either paste or powder form. The powder form is preferable for a 
number of reasons. While these poisons may be prepared at home, 
it is usually more convenient to buy the prepared article, which only 
needs to be stirred into water or Bordeaux mixture before being used. 
The directions for dilution are usually given on the containers. The 
amounts to be used in small quantities are given in Table I, page 30. 
Other poisonous substances are used occasionally, while some, like 
Paris green, were used extensively, almost exclusively, until super- 
seded by arsenate of lead and arsenate of lime. The lower cost and 
greater fineness and adhesiveness of the last two make their use most 
general now. 
Being violent poisons, these substances should be stored and handled 
with due caution, especially as regards live stock and children. 
THE CONTACT SPRAYS. 
As elsewhere stated, contact sprays are used to kill sap-sucking 
insects, like scale bugs, aphids or plant-lice, ete. Death is produced 
by the coating and clogging of their breathing pores, by affecting 
the nervous system, or by caustic action on the tissue of the insect, 
or by combinations of these. Lime and sulphur compounds, soaps, 
petroleum oils, and tobacco extracts are the active agents in these 
preparations. 
Lime-sulphur, miscible oil, kerosene emulsion, and 40 per cent nico- 
tine sulphate are contact sprays. With the exception of kerosene 
emulsion, which must be prepared at home, all of them are procurable 
commercially, where each is sold under a variety of proprietary 
names. All that they require to be made ready for application is to be 
stirred into water, with the addition of a little soap in the case of the 
nicotine. Directions for dilution are usually printed on containers 
and should be followed carefully. For small quantities see Table I, 
page 30 
LIME-SULPHUR. 
Lime-sulphur, as an insecticide, is used almost exclusively against 
the so-called armored scale insects, like the San Jose and oyster-shell 
scales, and principally as a dormant or early spring spray. It is the 
