12 



hoops. Ornamental plants of low-growing sorts ma}^ be fumigated by 

 means of such a hood, while for moderately high plants, such as roses, 

 which are much affected by two common species of aphides, special 

 covers ma}^ be constructed. 



VAPORIZING AND FUMIGATING TOBACCO IN GREENHOUSES. 



In the vaporization of tobacco — a practise which has been in use 

 since about 1894 and which has largely superseded ordinary dr3^-tobacco 

 fumigation in many sections^tobacco stems or dried tobacco, in one or 

 another of its various proprietary forms, are placed in a kettle, metal 

 pail, or similar receptacle. A hose is then connected with a steam 

 pipe, the nozzle inserted in the receptacle, and the house to be treated 

 becomes saturated with the vapor of tobacco, with the resulting 

 destruction of aphides and other soft-bodied insects that may be pres- 

 ent, such as thrips or "white fly." 



Liquid preparations are more generally evaporated over alcohol or 

 other lamps, or are placed upon steam pipes, or hot irons are put into 

 the receptacles. For general greenhouse fumigation, fumigating 

 powders are placed in shallow pans, and a few drops of kerosene are 

 added to facilitate ignition. The dry fumigant is designed to burn 

 slowl}', so as to produce a smudge which, when dense, is fatal to 

 aphides. This process of treatment may be applied at any time, by 

 day or over night, and upon its completion the house is ventilated. In 

 some cases the plants are syringed, but this is not necessary with plants 

 like cucumbers. A surplus of moisture is to be avoided, owing to the 

 liability of inducing ''spot," mildew, and other fungous diseases on 

 plants susceptible to such maladies. 



The amount of a tobacco compound to be used depends upon its 

 strength, the plants to be treated, and the size of the greenhouse. Sev- 

 eral forms are for sale under different trade names. It is not probable 

 that these differ greatly from one another in value, but there is much dif- 

 ference in their strength. They are put up in both dry and liquid forms. 



In experiments conducted on greenhouse cucumbers at the Massa- 

 chusetts Agricultural Experiment Station, at Amherst, one of these 

 preparations has been used successfully at the rate of 5 or 6 teaspoon- 

 fuls to li pints of water, and vaporized in a space of about 5,000 cubic 

 feet. The length of exposure in this case was over night. Thus used, 

 it does not injure delicate plants, like cucumber, but it kills all aphides 

 and nearly all thrips — for which it was used primarih^ and which are 

 not infrequently associated with aphides on the plants to be treated." 



"Thrips and "white fly" {Aleyrodes spp. ) are more resistant to poisonous gases 

 than are aphides. The former are most effectively destroyed while in the soft imma- 

 ture stages. The adult thrips are hardier and, being winged and more active, spring 

 and fly away, and are thus not so easily brought in direct contact with insecticides 

 like' kerosene emulsion. The white flies, on the other hand, are more susceptible 

 to poisons while in the active adult stage. The nymphs are of firmer consistency 

 and comparatively resistant. Remedies for the greenhouse white fly are discust in 

 Circular No. 57. 



