FUMIGATION OF NUESERY STOCK. 79 



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In limestone regions, or where the water is very hard, some of the 

 soap will combine with the lime or magnesia in the water, and more or 

 less of the oil will be freed, especially when the emulsion is diluted. 

 Before use such water should be broken with lye, or rain water 

 should be employed. 



For winter sprays dilute the emulsion with either 3, 4, or 5 parts of 

 water, giving a percentage of oil of approximately 17, 13, and 11 per 

 cent. The strength in oil of this application on trees as compared with 

 the oil-water sprays is the equivalent of 25, 20, and 15 per 'cent oil, 

 because relatively more of the heavier oil-soap emulsion is held by the 

 bark. The two stronger mixtures may be used on the apple and pear 

 and the weaker one on peach and plum. 



For summer applications dilute with 7, 10, or 15 parts of water, giv- 

 ing approximately 8, 6, and 1 per cent of oil. The weaker strengths 

 may be used on trees with tender foliage, such as that of peach, and the 

 greater strength for strong foliage plants, like the apple and pear. 



FUMIGATION OF NURSERY STOCK. 



All nursery stock which is under the least suspicion of contamination 

 with the San Jose scale should be fumigated; and it is perhaps worth 

 while to fumigate in any case to give the utmost assurance of safety 

 to the purchaser. The hydroc3^anic-acid-gas fumigation is the one to 

 use. This gas is generated by combining potassium cyanide, sulfuric 

 acid, and water. The proportions of the chemicals are as follows: 

 Refined potassium cyanide (98 per cent), 1 ounce; commercial sulfuric 

 acid, 1 ounce; water, 3 fluid ounces — to every 100 cubic feet of space 

 in the fumigating room or house. The latter should be as nearl}" air- 

 tight as possible and provided with means of ventilation above and at 

 the side, operated from without, so that at the end of the treatment 

 the poisonous gases can be allowed to escape without the necessit}^ of 

 anyone entering the chamber. The generator of the gas may be any 

 glazed earthenware vessel of 1 or 2 gallons capacit}^ and should be 

 placed on the floor of the fumigating room and the water and acid 

 necessary to generate the gas added to it. The cyanide should be 

 added last, preferably in lumps the size of a walnut. Promptl}^ after 

 adding the cyanide the room should be vacated and the door made 

 fast. The treatment should continue forty minutes. It must be borne 

 in mind that the gas is extrefnely poisonous and must under no circum- 

 stances be inhaled. The gas treatment is effective against the scale on 

 growing trees in the orchard also; but the difficult}^ and expense of 

 the treatment, except for nursery stock, make it prohibitive in the case 

 of deciduous fruits. 



8449— No. 62—06 6 



