22 MISC. PUB. 526, U. S. DEPT. OF AGRICULTURE % 
Another spray that may be used against lacebugs on such shrubs as 
azalea or rhododendron is: 
Derris or cube powder (4 percent of rotenone) _____. 5 tablespoonfuls. 
White oil emulsion (83 percent of oil) _-____________ % cup. 
Bie 5 2} feta ma Rs a PES So a 98 A 3 gallons. 
Some ornamental plants, including sweet peas, ferns, and orchids, 
are injured by oil sprays. Other plants may be injured where the spray 
collects in cavities or leaf axils; as the water evaporates, excess oil 
is left at these points. Palms and other plants having cavities in which 
spray material collects should be syringed with water or laid on their 
side after being sprayed with oils. Certain pyramidal junipers and 
spruces may also be injured by oil sprays. It is advisable to wash or 
syringe the more tender plants with water an hour or so after apply- 
ing the spray. 
Although oil emulsion can be prepared at home, it is much more 
te for the user of small quantities to purchase the prepared 
roduct. 3 
: Along with extract of pyrethrum, a white mineral oil or summer 
oil of 100 to 150 seconds viscosity (Saybolt, at 100° F.) is used to pro- 
tect sweet corn from injury by the corn earworm. The pyrethrum 
extract (sometimes called oleoresin of pyrethrum) having a 20- 
percent pyrethrin content is available on the market. To obtain a 
0.2-percent pyrethrin content, which is recommended, 38 ml. (or about 
11, fluid ounces) of this extract should be added per gallon of oil. 
Application of about 14 teaspoonful to each ear is made with a modi- 
fied force oiler (oil can) or with a medicine dropper, one-half or 
three-fourths full, according to the size of the ear. ‘Treatment is 
made immediately after the ears are fertilized, that is, as soon as the 
silks become wilted but not before about the third day after silk 
becomes exposed. 
NAPHTHALENE 
Naphthalene (C,,.Hs), obtained from coal tar, is generally sold as 
white crystalline flakes or as the well-known “moth balls.” Crude 
naphthalene is sold in flake and chip form and is colored by the im- 
purities present. Naphthalene vaporizes at a noticeable rate at room 
temperature, but the vapor, although detectable by its tarry odor, is 
not sufficiently concentrated to produce inflammable mixtures with air. 
The use of the refined product in clothes moth control is well known. 
A less refined material has been used as a soil treatment for wirewerm 
control in irrigated lands of the West and for the control of the carrot 
rust fly. Consult the State entomologist for information on its use 
locally for these pests. 
Naphthalene in the form of flakes or in solution in certain. solvents 
is also volatilized in greenhouses over lamps for the control of red 
spiders and thrips on carnations and certain other crops that will 
tolerate the fumes. The fumigations are carried out on cloudy days 
or at night at a temperature near 80° F. and with high humidity. 
From 2 to 3 ounces are used per 1,000 cubic feet of space, and the 
lamps are adjusted to volatilize the flakes evenly over a period of 
about 6 hours. The margin of safety between a dosage tolerated by 
plants and one toxic to insects is very narrow, therefore it should not 
be used in greenhouses except by experienced workers. 
