56 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



germinating power of seeds is quickly destroyed, but they are not 

 injured for food. 1 to 5 per cent of the gas, with an exposure of 

 twenty-four hours, is effective for most seed and grain pests. It 

 cannot be used on vegetation or for moist fruits. 



Tobacco Fumes. Tobacco is extensively used as a fumigant 

 for aphids in greenhouses and for certain plants, such as melons, 

 by using it under covers. Several forms are now commonly 

 used. Tobacco or nicotine extracts are sold under various trade 

 names, and are volatilize^ by heating either with a small lamp 

 or by dropping hot irons into the dishes containing the fluid. 

 The same material may be purchased in the form of paper which 

 has been saturated with the extract and which is burned accord- 

 ing to directions, a certain amount being sufficient for so many 

 cubic feet of space, which forms a more convenient method of 

 application. Certain finely ground tobacco powders, called 

 " fumigating-kind " tobacco powder, are used in the same way 

 and are much the cheapest form of tobacco for fumigation, 

 though requiring slightly more work in preparing for fumigation. 

 These tobacco preparations are excellent for the fumigation of 

 household plants, which may be placed in a closet and then 

 fumigated according to the directions of the particular brand 

 employed. Melon vines, young apple trees, bush fruits, and 

 similar outdoor crops may be effectively rid of plant-lice by 

 fumigating with tobacco-paper under a frame covered with 

 canvas or muslin sized with glue or linseed oil.* 



5. Application of Insecticides 



Insecticides, especially stomach poisons and contact poisons, 

 are usually applied in the form of a spray delivered under pressure 

 by a force pump, the liquid being broken up into a fine mist by 

 some kind of nozzle constructed for that purpose. As sprays 

 they are, of course, always mixed with water according to pro- 

 portions which will be mentioned at the proper places. In place 

 of pure water, bordeaux mixture or dilute lime-sulphur is some- 

 times used and the spray then serves the double purpose of con- 

 trolling insects and plant diseases. In some cases the fungicide, 



* For further discussion of Insecticides see Farmers' Bulletin 127, U. S. 

 Pepartment of Agriculture. 



