SPRAYING 



89 



their nourishment from within the tissues of the plant. Therefore, 

 a spraying material must be used for these insects that will kill 

 them by coming in contact with their bodies. Formerly kerosene 

 emulsion and whale-oil soap were used for spraying vegetable 

 crops attacked by plant lice and other sucking insects; but the 

 most approved treatment for plant lice on outdoor vegetables at 

 the present time is spraying with a solution of nicotine sulfate. 

 This is purchased in concentrated form and diluted with water 

 as needed for use. 



Fungous diseases of plants are caused by the development of 

 low forms of plant life, known as fungi, on or within the tissue of 

 the higher plant. These fungi secure their sustenance from the 



Fig. 49. — A fungus growing within the tissue of a leaf. 



plant on which they grow, and their development may result in 

 the partial or complete destruction of the host plant. Fungi are 

 propagated by spores, which correspond to the seeds of higher 

 plants. The spores are exceedingly small and in the case of many 

 fungi are carried about by the wind. If they find lodgement on a 

 susceptible host plant, and the conditions of temperature and 

 moisture are favorable for their germination, they start growth 

 and soon develop into plants that are securing their nourishment 

 at the expense of their hosts (Fig. 49). Spraying for the control 

 of fungous diseases involves the application of a material that 

 will either prevent germination of the spores or kill the germ tube 



