18 INSECTS NOXIOUS TO AGRICULTURE. 



Psyllidse, and Aleurodidse produce the same effects. This is by 

 110 means as well understood as it should be, either by gardeners 

 themselves or by those who write on trees and planting. The 

 fungus growth is usually imagined to be in itself a disease of 

 the plant, and efforts are made for its treatment without regard 

 to its real origin, the insects on the leaves or bark. Under the 

 names of " smut," " black blight," &c., it is often referred to as 

 a destructive pest ; and remedies are suggested which can, of 

 course, have no permanent effect unless they are equally effica- 

 cious against the insect producing the honeydew. It is pro- 

 bably from this cause that sulphur, which is an excellent 

 remedy against fungus, has been so great a favourite with those 

 who pretend to have discovered what are called (e scaly-blight 

 destroyers ; " and gardeners, seeing, perhaps, these nostrums 

 clean some of the fungus from their trees, are under the false 

 impression that the " scale " is also cleared away. The truth is_, 

 that the real remedy against " black blight " is to kill the 

 insects on whose excreta it nourishes, if that can be done. As 

 to the modes of doing this see Chapter V. 



It is not, of course, pretended here that fungi of different 

 kinds, and even those specially referred to, will not grow 

 independently of insects and honeydew; and trees are, un- 

 doubtedly, subject to fungoid diseases which are not to be traced 

 to any animal action. Still, the rule holds good; and the first 

 effort of a gardener on the appearance of black blight on his 

 plants should be to discover the insects on its leaves or bark, 

 and deal directly with them. Once they are destroyed the 

 fungus growth will in a short time disappear. 



