21 



must be strictly followed to insure the greatest success. Methods of experimenting 

 will be described in the latter part of this circular. The quantity of gas in each case 

 is always given in terms of the potassium cyanide from which it is made, and on a 

 basis of a cubic foot of space, as will be explained more in detail further on. The 

 cyanide, as well as the gas made from it, is exceedingly poisonous, and both must 

 be used with the greatest care. 



CROPS ANP PESTS OX WlirCU TfTE GAS HAS BEEN SUCCESSFUIJ>Y VSED. 



Femn. — For Davallia mooreana infested with a scale insect {CJiionaspis sp. ), 0.075 

 gram of 98 per cent potassium cyanide should be used for each cubic foot of space 

 to be fumigated, not deducting the space occupied by the ])lants. Length of expo- 

 sure, twenty minutes. 



One hundred and fifty to two hundred i)lants with fronds in all stages of develop- 

 ment have been thus treated two or three times each year for the past four years 

 with no injury to the plants and almost complete destruction of the insect. They 

 were treated fifty at a time in a fumigating box (fig. 4.) , described later. 



Adianium cuneatum and .1. Ballii have been tried on a small scale and were not 

 injured by the treatment. 



Coleus. — "Golden Bedder," " Verschaffeltii," " Shylock," au<l others. 24,000 

 plants in pots, badly infested with the "white-tailed" mealy bug {OrtJiezia insignis) . 

 The house contained 15,587 cubic feet of s])ace. Treated at the rate of one-tenth of 

 a gram of 98 per cent cyanide of jxjtash per cubic foot of space for twenty minutes, 

 one hour after dark. Orthezia all killed and jjlanta not injured in the least. All 



Fig. 4.— Fumigating box showing trays and coleus cuttings (from Woods and Dursett). 



other means of destroying the Orthezia had been tried without effect. Large num- 

 bers of the common mealy bug were also killed by this treatment; but it was not 

 nearly so effective as for the "white- tailed" mealybug. All coleus cuttings made 

 by the L^nited States Propagating Gardens for the i)ast two years have been fumi- 

 gated before being prepared for the cutting bed (see fig. 4). 



Double English violets. — "Marie Louise," "Lady Campbell," and others. Forplant- 

 lice and general fumigation fifteen-hundredths of a gram of 98 i)er cent cyanide of 

 potash for each cubic foot of space is required. The exposure, if made according to 

 directions, will not hurt the plants in any stage of growth. The gas has been used 

 on a large scale in fumigating violets for the past three years with the greatest suc- 

 cess, only a few treatments during the season being required. Leaf-eating larvae, 

 slugs, millipedes, cutworms, etc., when exposed are killed as well as plant-lice. 

 Red spiders, however, are not entirely eradicated by the treatment. The foliage of 

 single violets like California and Princess of Wales are sometimes slightly injured 

 by the stronger dose of gas. A weaker dose (one-tenth of a gram potassium cyanide 

 per cubic foot) should be used when they are to be treated. 



