12 MISC. PUB. 5 2 6, U. S. DEPT. OF AGRICULTURE 



Gypsum (landplaster) . — Chemically this is calcium sulfate 

 (CaS0 4 .2H 2 0), a white or yellowish-white powder. It is used with 

 calcium arsenate in the control of cucumber beetles. 



Hydrated lime. — See page 14. Chemically this is calcium hy- 

 droxide (Ca(OH) 2 ) and is commonly used with arsenicals and as a 

 carrier in nicotine dusts. 



Pyrophyllite. — Chemically this is anhydrous aluminum silicate 

 (HAL (Si0 3 ) 2 ), white, and is very similar to talc in physical prop- 

 erties. It has recently come into general use as a diluent for cube 

 and derris. 



Sulfur. — See page 35. 



Talc. — In the solid form this material is known as soapstone. 

 Chemically it is a magnesium silicate (H 2 Mg 3 (Si0 3 ) 4 ). As marketed 

 as an insecticidal diluent it is usually a white or grayish-white 

 powder composcl of microscopic platelike particles that give it a 

 smooth feel. It is used in derris and cube dust mixtures. 



Tobacco dust. — See page 37. 



Walnut-shell flour. — This is a brown powder obtained by finely 

 grinding the shells of Persian ("English") walnuts. It is used in the 

 preparation of impregnated dusts. It is not so suitable as talc as a 

 diluent for rotenone-containing roots (derris and cube). 



Wheat flour. — This is the ordinary "white" wheat flour familiar to 

 all. 



DINITRO COMPOUNDS 



These are organic compounds manufactured in this country which 

 have come into general use in certain fruit-growing districts for the 

 control of scale insects, the fruit tree leafroller, the pear psylla, the 

 bud moth, mites, and aphids. 



They are of two types, (1) those that are sold in powder form to be 

 added by the grower to lubricating-oil sprays, and (2) those sold 

 in liquid form to be added to water. The former group includes 

 dinitro-o-cyclohexylphenol and dinitro-o-cresol. The principal com- 

 pound in the second group is sodium dinitro-o-cresylate. Dinitro- 

 o-cyclohexylphenol is also used on citrus as a contact insecticide in 

 the form of a diluted dust to kill the citrus red mite, and it may be 

 used on potato and bean to control the potato leafhopper. 



These materials should be used according to the manufacturers' 

 recommendations, since they may contain diluents in varying amounts. 



The oil-soluble powdered forms, when added to dormant spray oils, 

 generally reduce the quantity of oil required. 



Dinitro insecticides as now used should be applied to deciduous trees 

 only while the buds are dormant. 



When property used, these compounds present no special hazard 

 to human health. 



ESSENTIAL OILS 



Essential oils are volatile, aromatic materials obtained from plants, 

 usually by steam distillation, and have odors generally characteristic 

 of the plant source. 



They are employed as attractants in insect traps. The essential oils 

 by themselves are relatively nontoxic. 



