386 economic entomology 



2. The Application of Contact Substances Against Sucking 



Insects 



(Consult Farmers' Bull. 908, U. S. Dep. Ag.) 



The main substances used as Contact Insecticides against sucking 

 insects are: {a) Lime-sulphur wash; {b) whale-oil soap; (c) kerosene 

 emulsion; {d) tobacco decoction; {e) miscible oils; (f) pyrethrum; {g) 

 lime dust; {h) commercial sodium fluoride; ii) carbolic acid emulsion, 

 {j) other substances. 



(a) Lime-sulphur Wash. — This wash first came into use in the control 

 of the San Jose scale on dormant wood where its beneficial eff'ects 

 were evident also against other insects and against certain fungous 

 diseases. It cannot be used on potato leaves. 



It is prepared in two forms — home-made lime-sulphur wash and 

 commercial lime-sulphur wash, diluted for use on dormant wood 

 and on summer foliage as required. 



I. Home-made Preparation (Boiled). — Lime (best), 20 lb.; sulphur 

 (flowers), 15 lb.; water, 40 gal. (imperial).^ 



II. Concentrated Formula (Stock Wash). — Lime, 50 lb.; sulphur 

 100 lb.; water, 40 gal. (imperial) or 50 gal. U. S. measure. 



Heat water (20 gal.) to near boiling and add the fresh lime. While 

 slaking is in progress add with frequent stirrings the sulphur which 

 has been made into a paste. Add water to make up to 40 gal. and 

 boil for an hour replacing the water lost by boiling. Strain through 

 a 20-mesh screen, and place in storage barrels. By means of a lime- 

 sulphur hydrometer the amount of dilution can be determined for 

 each spraying. ''For use before buds burst" dilute to sp. gr. 1.03; 

 "before blossoms burst" 1.009; and "just after blossoms fall," 1.008. 

 To get the amount of dilution divide the reading after the decimal 

 point of the stock solution by the reading after the decimal point 

 of the solution desired. For example, if the hydrometer reading of 

 the stock solution is 1.3 and that of solution, to use "before buds 

 burst" is 1.03, the amount of dilution is 30 divided by 3 = 10. That 

 is I gal. of stock solution makes 10 gal. of spray (Fig. 250). 



Some recent experiments go to show that the lime-sulphur applica- 



^The capacity of a barrel is expressed in all cases in imperial gallons (40); 

 sometimes the equivalent in U. S. measure (50) is also given. 



