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. 



Water 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 

 satisfactory for the user of small quantities to purchase the prepared 

 product. 



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 

 I14 fluid ounces) of this extract should be added per gallon of oil. 

 Application of about ^ 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 10 H 8 ), 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 wirew T orm 

 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. 



