18 INSECTS NOXIOUS TO AGRICULTURE. 
Psyllide, and Aleurodidz produce the same effects. This is by 
no means as well understood as it should he, either by gardeners 
themselves or by those who write on trees and planting. The 
fungus growth is usuaily 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 ‘ 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 flourishes, 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 msects 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 imsects on its leaves or bark, 
and deal directly with them. Once they are destroyed the 
fungus growth will in a short time disappear. 
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