214 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY, 
nurserymen nowadays are fully alive to this danger and do their 
utmost to check it. Many cases have nevertheless occurred in the 
past. One of the most conspicuous is that of the disease known 
as Big Bud in black currants, caused by the presence of the mite 
Eriophyes ribis. Before the nature of the disease was known the 
swollen buds due to it were thought to indicate especially healthy 
bushes, and were propagated and distributed under that idea. Even 
now that the disease is known, I do not believe that many nurserymen 
would dare to guarantee their stock free from it, so difficult is it to 
detect if present in only small quantity. 
There is a third cause that may or may not have had influence on 
the growth of insect pests, and that is man's interference with natural 
agents. When man starts cultivating land that was previously under 
natural vegetation he immediately begins to disturb the balance of 
Nature. Perhaps he cuts down trees and so disturbs the nesting- 
places of insectivorous birds, or perhaps he deliberately kills certain 
birds which he considers harmful to himself, but which may be at the 
same time of use in keeping down noxious insects. 
So, too, when he plants acres and acres of fruit he alters the balance 
of Nature, which had previously existed under purely agricultural 
conditions. But little is known of this complicated and interesting 
subject, and I do no more than suggest it tentatively as a third cause 
of increase of insect pests. 
Whatever the causes, the fact remains that insect pests have 
greatly increased in the last few decades, and that, were no control 
measures put in force, crops would be reduced to a minimum. 
Up to now, chemical methods, and especially spraying, have proved 
themselves the most efficient. They are, perhaps, the most direct 
in action, and usually give the quickest results. One must remember, 
however, that the whole question of insect control is in its infancy ; 
and, because spraying is the best means available at present, it 
by no means follows that no other methods will subsequently prove 
of greater avail. Already the interesting work done on parasites 
of economic insects in America, and the success that has been obtained 
by the use of bacterial diseases of the locust, indicate other and possibly 
more far-reaching means of control. At present, however, spraying 
undoubtedly holds the field, and it may be well to consider the 
question from as broad a point of view as possible. 
One frequently meets people who seem to think that spraying is 
a necessary thing in itself in fruit-growing. They appear to regard 
it in much the same way as many people regard patent medicines, 
with the eye of faith. They read, in the advertisements of pro- 
prietary spray -fluids, that such and such a one will kill every egg, 
insect, and fungus spore that is present on a tree, and with touching 
faith they apply it without troubling to notice whether their trees 
happen to be afflicted with these same diseases or not. I do not 
mean to say that all proprietary spray fluids are useless, but I do 
insist strongly that much blind and unprofitable spraying is done. 
