THE TREATMENT OF INSECTS AND FUNGI IN THE UNITED STATES. 195 



usually occurs at about the time the seed sprouts, so that the 

 destruction of the spores that may be on the seed is often 

 sufficient to ensure practical immunity. In perennials the only 

 thing usually to be done is the removal and destruction of the 

 infested plants. Some diseases of trees due to these fungi may 

 possibly be controlled by preventing the spread of the disease 

 (by spores), by the [use of the remedies that are so effectual 

 against the local fungi, and by vigorous pruning and removing 

 of new growth, in which the disease is chiefly carried over from 

 one season to another. This is, at least at present, the most 

 promising line of experiment in these cases. The experience in 

 some parts of California with curl-leaf, where it seems to be 

 entirely controllable, would seem to indicate that the disease is 

 not, in every region, to be properly classed with these penetrating 

 fungi. Further study may show that in certain seasons or in 

 certain regions the disease may arise from a local, and in others 

 from a penetrating fungus, and so in one place be easily con- 

 trolled, and in another not at all controllable without the 

 destruction of the plants affected. 



REMEDIES. 



There are a great many substances that may be used success- 

 fully against insects and fungi ; but we recommend only a small 

 list, selected because of their effectiveness and cheapness. 

 Remedies are applied as a dry powder, as a gas, or as a fluid, 

 spray or wash, the great majority being in the latter form. 



Powdeks. 



The most common way of applying powders is the " pepper- 

 box " method, in which the material is carried in a vessel pro- 

 vided with perforations, through which it sifts as the vessel is 

 shaken over the plant. A modification of this, much used 

 in the cotton fields of the Southern States, consists of bags 

 of the material suspended from the ends of a pole long enough 

 to reach from one row of cotton to the next. This is carried 

 by a man riding on a mule, and the jar causes the powder to 

 sift through. Cloth is chosen for this purpose, which is fine 

 enough to allow only the right quantity to be distributed. A 

 third method, much used in this country, is a blowing device, 

 which is very satisfactory for field use, and does very rapid work. 



