222 MISC. PUBLICATION 273. U.S. DEPT. OF AGRICULTURE 



The stomach-poison spray most frequently used for the control 

 of leaf -chewing defoliators consists of the following: Lead ar- 

 senate, l 1 ^ to iy 2 pints of the paste or 3 to 5 pounds of the 

 powder, fish-oil soap 5 to 6 pounds; and water to make 100 gallons. 

 Contact insecticides are used against small sucking insects 

 such as the aphids, scales, and bugs, and sometimes against small 

 caterpillars and leaf miners, and are applied in the form of liquid 

 sprays or dusts so as to come in direct contact with the insects. 

 These poisons kill the insects by entering the respiratory system, 

 or by penetrating through the thin body membranes, or they 

 may destroy them by plugging their breathing tubes, paralyzing 

 the nerve centers, or actually burning the insects through the 

 caustic properties of the chemicals. The young insects are much 

 more easily killed by such treatment than the older forms, which 

 often become resistant. 



There are a large number of contact sprays and dusts, each 

 with certain advantages and special fields of usefulness. Only a 

 few will be mentioned here, since the contact sprays, while very 

 useful in the control of shade-tree pests, have not as yet been 

 used in the forests of the West. 



One of the most useful contact sprays in the control of aphids 

 and other soft-bodied insects contains 1 pint of 40-percent nico- 

 tine sulfate and 5 pounds of fish-oil soap in water to make 100 

 gallons. 



Miscible oils have come into prominence in recent years for use 

 on shade and orchard trees, and are useful in nurseries and plan- 

 tations against such forest pests as the spruce gall aphid, the 

 green spruce aphid, and various scales. These oils are sold under 

 various names, and they vary somewhat in strength. The winter 

 oils are used as dormant sprays and will injure foliage if applied 

 when the trees are in leaf. Summer oils, which can be applied to 

 the foliage without injury, are also available. Instructions as to 

 dilution of the oils come with the product. Fish-oil soap is often 

 used as a spreader. 



Lime-sulfur is a very effective and inexpensive spray material 

 which is used in the control of the armored scales. It is applied 

 during the winter or early in the spring as a dormant spray. The 

 concentrated preparation should have a density of about 30° 

 Baume and should be diluted with 8 parts of water. 



DDT, benzene hexachloride, and chlordane, have largely re- 

 placed some of the older insecticides. Each of these new insecti- 

 cides is especially potent against certain groups of insects, yet 

 ineffective against others; so no one insecticide can be used for 

 all purposes. DDT, for instance, is outstandingly effective against 

 most caterpillars and sawflies, which constitute the bulk of the 

 important western forest defoliators, but is ineffective against 

 aphids and mites. 



Technical DDT is a gray or cream-colored lumpy powder, with 

 which various insecticidal formulations are prepared. For control 

 of forest defoliators four general types of preparations may be 

 used: (1) Dusts, in which DDT is mixed with a dry carrier; (2) 

 wettable powders, which are mixed with water to form suspen- 



