6 BULLETIN 513, U. S. DEPAETMENT OF AGRICULrURE. 



and this fact should be considered where an assortment 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^Hs preferable that the 

 initial dosage be not over one-fourth ounce of sodium cyanid per 

 1,000 cubic feet and increased with subsequent fumigations 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 abso- 

 lute control of all stages of some insects with one fumigation with- 

 out injury to foliage or growing parts of certain plants. For ex- 

 ample, the greenhouse white fly has been eradicated with three suc- 

 cessive fumigations at intervals of 7 to 9 days, using one-half ounce 

 of sodium cyanid (NaCN) per 1,000 cubic feet, in houses containing 

 such susceptible plants as coleus, ageratum, heliotrope, fuchsia, etc., 

 with no injury to the foliage. Moreover, such resistant pests as scale 

 insects can be eliminated entirely by killing the immature stages with 

 a small dosage repeated at frequent intervals. 



Under favorable conditions houses which do not contain roses, rose 

 geraniums, asparagus ferns, lemon verbena, snapdragon. Wandering 

 Jew, or sweet peas can be fuixdgated with safety with an initial 

 dosage of one-half ounce of sodium cyanid (NaCN) per 1,000 cubic 

 feet. 



To determine the total amount of cyanid to be used, ascertain from 

 the tables on pages 12-18 the plants in your greenhouse which are most 

 easily injured by the gas fumes and note the amount of cyanid which 

 was used per 1,000 cubic feet with little or no injury to the plants. 

 Then multiply the number of thousand cubic feet contained in the 

 house by the amount of cyanid to be used per 1,000 cubic feet. For 

 example, if one-half ounce of cyanid is to be used per 1,000 cubic 

 feet, and the house contains 15,000 cubic feet, the total amount of 

 cyanid necessary would be 7^ ounces. 



In case there is any doubt as to the amount of gas the plant can 

 stand without injury, the initial dosage, as previously stated, should 

 not exceed one-fourth ounce per 1,000 cubic feet. 



CHEMICAL FORMULA TO BE EMPLOYED. 



The chemicals ^ should be mixed in the following proportions : For 

 each ounce of sodium cyanid use 1^ fluid ounces of sulphuric acid and 

 2 fluid ounces of water. 



1 If potassium cyanic! is used in place of sodium cyanid, the formula should be aa 

 follows : For each ounce of 98 to 99 per cent potassium cyanid containing 38.4 per cent 

 cyanogen use 1 ounce of sulphuric acid and 3 ounces of water. The yield from 1 ounce 

 of high-grade sodium cyanid is equivalent to the yield from IJ ounces of high-grade 

 potassium cyanid. 



