July 7. 1921 



The Rorists^ Review 



19 



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FUMIGATION WITH 



SODIUM CYANIDE 



OST members of the trade 

 are well aware that potas- 

 sium cyanide, as a genera- 

 tor of hydrocyanic acid gas, 

 has been superseded by so- 

 dium cyanide, a slightly 

 stronger chemical. The Ee- 

 view has repeatedly supplied compre- 

 hensive instructions in regard to fumi- 

 gation with potassium cyanide and has 

 also given briefer suggestions about the 

 use of sodium cyanide. The directions 

 ■\7hich here follow, and which have refer- 

 ence chiefly to sodium cyanide, consist 

 of extracts from a bulletin prepared by 

 members of the TJ. S. Department of 

 Agriculture. 



The authors of the bulletin, E. E. Sass- 

 cer and A. D. Borden, state that "the 

 yield of cyanogen from one ounce of 

 high-grade sodium cyanide is equivalent 

 to the yield from one and one-third 

 ounces of high-grade potassium cya- 

 nide." "With that ratio as a basis of 

 computation, growers who have used 

 potassium cyanide should be able to 

 estimate the needed quantities of so- 

 dium cyanide. 



Computing the Cubic Contents. 



It is essential in every instance, says 

 the bulletin, that the cubic contents of 

 the house to be fumigated be deter- 

 mined accurately, and the following is 

 a simple method of arriving at these 

 figures: 



To secure the cubic contents of the 

 even-span house in the accompanying 

 diagram, compute the number of square 

 feet in the rectangle A and in the right- 

 angle triangles B and C and multiply 

 the sum of the three by the length of 

 the house. To calculate the area of a 

 right-angle triangle, multiply the base 

 by the perpendicular and divide the 

 product by 2, For example, A=5X20 

 =100 square feet; B=5X10->2=25 

 square feet; and C=5XlO-s-2=25 

 square feet. A+B+C=150 square 

 feet; 150 square feet X 100 feet (length 

 of house) =15,000 cubic feet, cubic con- 

 tents of the house. 



To secure the cubic contents of the 

 three-quarter-span house in the dia- 

 gram, multiply the sum of the rectangles 

 A and D and right-angle triangles B 

 and C by the length. For example, 



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f I c 



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o a 



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A=6X8=48 square feet; D=18X5=90 

 square feet; B=6X4-h2=12 square 

 feet; and C=18X 7-^-2=63 square feet. 

 A+D+B-|-C=213 square feet; 213 

 square feet X 100 feet (length of house) 

 =21,300 cubic feet, cubic contents of 

 house. 



In estimating the cubic contents of a 

 greenhouse it is not necessary to make 

 allowances for the space occupied by the 

 benches, pots, etc. 



When to Fumigate. 



Fumigation should be conducted not 

 earlier than one hour after sunset and 

 should not be attempted when the wind 

 is high. It is undesirable to fumigate 

 during extremely cold nights, when the 

 thermometer is registering near zero, 

 owing to the necessity of ventilating 

 the houses upon the completion of an 

 exposure. It is inadvisable to fumigate 

 on hot, humid nights, when the tem- 

 perature in the house can not be lowered 

 readily to the desired limit. The best 

 temperature for fumigation is between 

 55 and 68 degrees. 



The interval between fumigations 

 naturally should be governed by the 

 reappearance of the insect under con- 

 trol. "With small dosages, which are 

 imperative when fumigating a house 

 containing an assortment of plants, it is 

 possible to kill only the larvse of scale 

 insects, the adults and first larval 

 stages of the greenhouse white fly, the 

 adults of the Florida fern caterpillar, 

 greenhouse leaf -tier, and loopers, and a 

 certain percentage of aphids. The eggs 

 and pupa; of most greenhouse insects 

 offer considerable resistance to hydro- 

 cyanic acid gas; furthermore, the over- 

 lapping of broods necessitates several 



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Illustrating the Method of Calculating Cubic Contents of Greenhouses. 



fumigations at short intervals. It has 

 been proved repeatedly that three or 

 four fumigations at short intervals will 

 give practical control. 



The Necessary Chemicals. 



The chemicals required in fumigating 

 with hydrocyanic acid gas are sodium 

 cyanide or potassium cyanide, sulphuric 

 acid and water. Potassium cyanide has 

 been superseded recently by sodium cya- 

 nide in the generation of this gas, and 

 the former is rarely used nowadays in 

 fumigation. Sodium cyanide should be 

 practically free from chlorine and con- 

 tain not less than fifty-one per cent of 

 cyanogen. It may be purchased either 

 in lumps or in the shape of an egg, each 

 "egg" weighing approximately one 

 ounce. The latter is easily handled and 

 the necessity of weighing each charge is 

 obviated, provided, of course, the dos- 

 age is in ounces. For example, if the 

 house requires ten ounces of cyanide, 

 ten "eggs" are used. However, in 

 small dosages, where the cyanide is 

 measured in grams, it is necessary to 

 use small lumps or break up the ' ' eggs. ' ' 



Cyanide is one of the most poisonous 

 substances known and should be stored 

 in air-tight cans, plainly labeled, and 

 kept out of reach of those unacquainted 

 with its poisonous nature. 



Commercial sulphuric acid, which 

 is approximately ninety-three per cent 

 pure, is commonly used and gives satis- 

 factory results. The acid should be 

 kept in a glass receptacle, properlv la- 

 beled, and tightly corked with a glass 

 stopper. 



Estimating the Quantity. 



Satisfactory results are obtained onlv 

 where it is possible to overcome the re- 

 sisting power of the insects without 

 overcoming the resisting power of the 

 plants. Tender succulent plants, such 

 as roses, geraniums, coleus, sweet peas, 

 wandering jew, etc., are more susceptible 

 to injury by hydrocyanic acid gas than 

 are certain hardy ornamentals, and this 

 fact should be considered where an as- 

 sortment of plants is to be fumigated. 

 In case there is any doubt as to the 

 amount of gas a plant will stand without 

 injury, it is preferable that the initial 

 dosage be not over one-fourth ounce oi" 

 sodium cyanide per thousand cubic feet 

 and increased with subsequent fumi- 

 gations until the fatal point of the pest 

 to be controlled is reached, it being 

 borne in mind that in some instances it 

 is not possible to effect an absolute 

 control of all stages of some insects 

 with one fumigation without injury to 

 foliage or growing parts of certain 

 plants. For example, the greenhouse 

 white fly has been exterminated with 

 three successive fumigations at inter- 

 vals of seven to nine days, using one- 

 half ounce of sodium cyanide per thou- 

 sand cubic feet, in houses containing 



