DISEASES AND INSECTS 



DISEASES AND INSECTS 1045 



immediately, before the gas arises. Fig. 1323 shows a 

 device used abroad (from the "Gardening World") for 

 dumping the cyanide (at 4) into the acid by means of a 

 cord that extends outside the house. 



White-fly. The quantity of chemicals used for a 

 given space will depend on the nature of the insects to 

 be killed and the susceptibility of the plants to injury. 

 This quantity is usually indicated by amount of 

 potassium cyanide required for each 100 cubic feet of 

 space. For treating white-fly on tomatoes in green- 

 houses, use one ounce to 3,000 cubic feet, letting the 

 fumigation continue all night. The same treatment 

 applies for cucumber. Fumigate on dry, dark nights 

 when there is no wind. The house should be as dry 

 as practicable and the temperature not above 60 F. 



Greenhouses. No one formula can be given for 

 fumigating with hydrocyanic acid gas the different 

 kinds of plants grown in greenhouses, as the species 

 and varieties differ greatly in their ability to withstand 

 the effects of the gas. For the general run of greenhouse 

 subjects, the practice is to use one ounce of potassium 

 cyanide, one ounce of sulfuric acid, two ounces water, 

 to each 2,000 cubic feet of space. The cyanide should 

 be 98 per cent pure. Fumigate at night when there is 

 no wind and when the plants are dry and the house 

 cool; leave the house closed till morning, and open it 

 up and let it air out before entering it. This applies 

 to chrysanthemums, cinerarias, azaleas, bulbs, carna- 

 tions and other common plants. 



Ferns and roses are very susceptible to injury, and 

 fumigation, if attempted at all, should be performed 

 with great care. In cases of doubt, or when there 

 is reason to suspect that the plants are particularly 

 susceptible, and when 

 one does not have 

 definite instructions, 

 it is well to fumigate 

 with the weakest 

 strength in use, and 

 increase it in sub- 

 sequent fumigations 

 if the insects are not 

 killed and if the plants 

 are not injured. 



Violets are very 

 susceptible to injury 

 from tobacco fumiga- 

 tion, and commercial 

 growers therefore reg- 

 ularly use hydrocy- 

 anic acid gas for the 

 control of green-fly" 

 and "black-fly," two 

 species of plant-lice. 

 The latter is much 

 more difficult to kill. 

 For over-night fumi- 

 gation from one- 

 fourth to one-half 

 ounce potassium 

 cyanide to each 1,000 

 cubic feet is generally 

 used. Sometimes one 

 ounce potassium 

 cyanide to each 1,000 

 cubic feet is used, the 

 fumigation continuing 

 only from twenty-five 

 to thirty-five minutes 



of two thicknesses of matched boards with building- 

 paper between, and are provided with a tight-fitting 

 door and ventilators. The stock should be reasonably 

 dry to avoid injury, and should be piled loosely in the 

 house to permit a free circulation of the gas. Use one 

 ounce of potassium cyanide for each 100 cubic feet of 

 space, and let the fumigation continue forty minutes 

 to one hour. 



A fumigating-house is shown in Fig. 1324 (from a 

 bulletin on "The San Jos< Scale," by A. E. Stene, of 

 the Rhode Island State Board of Agriculture and Col- 

 lege of Agriculture). It is a house or box as nearly air- 

 tight as possible. The floor should have a movable slat 

 grating on which the plants may be laid, some distance 

 from the ground, to allow of circulation of the gas. 

 The house shown in the cut is 8 feet high in front and 

 6 feet in rear, and the larger room contains 980 cubic 

 feet, requiring approximately ten ounces of cyanide. 

 The other rooms allow of smaller quantities to be 

 fumigated. The doors opening from the outside provide 

 quick discharge of the air when fumigation is completed. 



Fumigation of citrus trees. In this case, the tree to 

 be fumigated with the hydrocyanic acid gas is covered 

 with an octagonal sheet tent (Fig. 1325) made of six 

 and one-half ounce special drill or eight-ounce special 

 army duck, and the gas is generated in the ordinary 

 way beneath it. The tent is so marked that when in 

 position it is an easy matter to determine the distance 

 over the tent and the circumference at the ground. 

 When these figures are known, the proper dosage may 

 be obtained from the following chart, which has been 

 prepared for a strength of one ounce of cyanide for 

 each 100 cubic feet of space: 



Dosage chart for fumigating citrus trees with high-grade sodium cyanide (Bureau of Entomology, 

 United States Department of Agriculture) . 



This treatment is more likely to injure the plants. 

 Violets may be injured severely by the gas without the 

 leaves being burned. This injury consists in a weakening 

 of the plants which defers blooming for several weeks. 

 Dormant nursery stock may be fumigated with hydro- 

 cyanic acid gas in a tight box or fumigating-house made 

 especially for the purpose. Fumigating-houses are built 



The top line of numbers, beginning at 16 and con- 

 tinuing to 68, represents the distance in feet around 

 the bottom of the tent. The outer vertical columns of 

 larger numbers running from 10 to 49 represent the 

 distance in feet over the top of the tent. The number 

 of ounces of cyanide to use for a tree of known dimen- 

 sions is found in that square where the vertical column 



