164 The Spraying of Plants. 



kerosene and similar insecticides. The oil is particularly abun- 

 dant in the flower-heads just before they open, and the plant is 

 best cut at this time. The stems also are used, and they may 

 form about one-third of the mass to be ground into powder. 

 The oil is very volatile, so the dried plants should not be exposed 

 to the rays of the sun, to a high temperature, nor to moisture. 

 After being dried, they should be placed in a receptacle which 

 can be tightly closed; and it is imperative that the powder be so 

 treated, else it will quickly lose its strength. 



There are two species of Pyrethrum which furnish the bulk 

 of the commercial articles. P. roseum is the plant that is 

 native to the province of Transcaucasia, and from it is obtained 

 the form sold as Persian insect powder. P. cineraricefolium, 

 however, is native to Dalmatia, and Dalmatian insect powder 

 is the product derived from this plant. Buhach is obtained 

 from a cultivated form of the same species. This plant is the 

 one mostly grown in California, and for this reason Buhach is 

 the most reliable powder to use. The insecticidal value of the 

 plant does not appear to diminish under cultivation, and, as 

 Buhach is made in this country, it is more apt to be fresh. 

 Both species are cultivated as ornamental plants, and it is prob- 

 able that they have equally valuable insecticidal properties. 



Pyrethrum can be used in a great variety of ways, of which 

 the following are the most important : 1 



"1. In solution. One ounce to 3 gallons of water. 



"2. Dry, without dilution. In this form it is excellent for 

 thrips and lice on roses and other bushes. Apply when the 

 bush is wet. Useful for aphis on house plants. 



" 3. Dry, with dilution. Diluted with flour or any light and 

 fine powder. The poison may be used in the proportion of 1 

 part to from 6 to 30 of the diluent. 



" 4. In fumigation. It may be scattered directly upon coals, 

 or made into small balls by wetting and moulding with the 

 hands, and then set upon coals. This is a desirable way of 

 dealing with mosquitoes and flies. 



" 5. In alcohol. (1) Put 1 part of pyre thrum (buhach) and 

 4 parts alcohol, by weight, in any tight vessel. Shake occa- 

 sionally, and after eight days filter. Apply with an atomizer. 

 Excellent for greenhouse pests. For some plants it needs to be 



i Bailey, " Horticulturist's Rule-Book," third edition, 1895, 10, 11. 



