FUMIGATION OF ORNAMENTAL GEEENHOUSE PLANTS. 9 



conducted where the plants, beds, and walks were thoroughly soaked 

 with water, and the injury which would be expected under normal 

 conditions to such plants as cosmos, rose geraniums, roses, helio- 

 tropes, and Asparagus plumosus did not appear, nor were such in- 

 sects as aphids and thrips appreciably affected. It is obvious, there- 

 fore, that in order to increase the effectiveness of the fumigation the 

 plants should be syringed not less than four or five hours prior to the 

 liberation of the gas, to avoid undue absorption of the gas by the 

 water on the benches and walks. 



The difference in the results noted above may he accounted for by 

 the fact that in the case of box fumigation only the foliage was cov- 

 ered with a film of water, whereas in the case of the greenhouse ex- 

 periments not only the foliage of the plants was covered with a film 

 of water but the entire soil surface of the house was soaked, and the 

 water undoubtedly absorbed much of the available gas, reducing the 

 toxic effect of the gas on the plants and insects. 



HUMIDITY. 



Eecent tests have demonstrated that a relatively high humidity 

 (98 to 100), with temperature varying from 70° to 75° F., greatly 

 increases the amount of injury to the foliage of the plants, whereas 

 plants in the presence of a relatively high humidity (98 to 100), with 

 a temperature of 60° to 65° F., do not exhibit injury in excess of that 

 which would appear if the plants were fumigated with an excessive 

 dosage under normal atmospheric conditions. It is apparent, there- 

 fore, that a relatively high humidity alone is not responsible for 

 injury unless accompanied by temperatures exceeding 70° F. 



ADVISABILITY OF A FUMIGATION BOX. 



A fumigation box is desirable for two reasons, namely, for testing 

 the amount of gas plants can stand without injury, and for ridding 

 a limited number of potted plants of insects, and thus avoiding costly 

 and laborious hand scrubbing of such plants. The size of the box will 

 depend on the use to w^hich it is to be put. A box with a capacity 

 of 200 cubic feet can be used advantageously for nursery stock, 

 palms, etc. 



Plants to be fumigated in a box in the daytime should remain in 

 the box with the door closed at least one hour before the gas is gen- 

 erated and should be shaded from the bright sunlight for at least 

 two hours after the completion of the exi3osure. 



HOW INSECTS ARE DISSEMINATED FROM HOUSE TO HOUSE. 



Doubtless many houses become infested with insects through the 

 agency of plants commonly referred to as " boarders." The practice 

 of turning over home-grown plants to a florist to care for during the 



71777°— Bull. 513—17 2 



