FUMIGATION OF ORNAMENTAL GREENHOUSE PLANTS. 5 



tilating the houses upon the completion of an exposure. It is inad- 

 visable to fumigate on hot, humid nights, when the temperature in 

 the house can not be lowered readily to the desired limit. The best 

 temperature for fumigation is between 55° and 68° F. 



The interval between fumigations naturally should be governed 

 by the reappearance of the insect under control. With small dos- 

 ages, which are imperative when fumigating a house containing an 

 assortment of plants, it is possible to kill only the larvae of scale in- 

 sects, the adults and first larval stages of the greenhouse white fly, 

 the adults of the Florida fern caterpillar, greenhouse leaf-tyer, and 

 loopetrs, and a certain percentage of aphids. The eggs and pupse 

 of most greenhouse insects offer considerable resistance to hydro- 

 cyanic-acid gas, and furthermore the overlapping of broods necessi- 

 tates several fumigations at short intervals. It has been proved 

 repeatedly that three or four fumigations at short intervals will give 

 practical control. 



CHEMICALS REQUIRED FOR FUMIGATION. 



The chemicals required in fumigating with hydrocyanic-acid gas 

 are sodium cyanid (NaCN) or potassium cyanid (KCN), sulphuric 

 acid (H2SO4), and water (HoO). Potassium cyanid has been super- 

 seded recently by sodium cyanid in the generation of this gas, and 

 the former is rarely used nowadays in fumigation. Sodium cyanid 

 should be practically^ free from chlorin and contain not less than 51 

 per cent of cyanogen. It may be purchased either in lumps or in the 

 shape of an egg, each ^''egg'''' weighing approximately 1 ounce. The 

 latter is easily handled and the necessity of weighing each charge is 

 obviated, providing, of course, the dosage is in ounces. For example, 

 if the house requires 10 ounces of cyanid, 10 " eggs " are used. How- 

 ever, in small dosages, where the cyanid is measured in grams, it is 

 necessary to use small lumps or break up the " eggs." 



Cyanid is one of the most poisonous substances known and should 

 he stored in air-tight cans, plainly labeled, and kept out of reoxih of 

 those unacquainted with its poisonous nature. 



Commercial sulphuric acid (about 1.84 sp. gr. or 66° Baume) 

 which is approximately 93 per cent pure is commonly used and gives 

 very satisfactory results. The acid should be kept in a glass re- 

 ceptacle, properly labeled, and tightly corked with a glass stopper. 



DETERMINING THE AMOUNT OF CYANID TO BE USED. 



Satisfactory results are obtained only where it is possible to over- 

 come the resisting power of the insects without overcoming the resist- 

 ing power of the plant. Tender succulent plants, such as roses, gerani- 

 ums, coleus, sweet peas. Wandering Jew, etc., are more susceptible to 

 injury by hydrocyanic-acid gas than are certain hardy ornamentals. 



