SOME ASPECTS OF SPRAYING AGAINST PESTS. 
225 
clean, but at the same time becomes what is known as hidebound. 
The bark, even in winter, is not dead, and an annual winter washing 
is liable to cause a certain amount of injury. There are, however, 
certain circumstances in which a winter cleansing is fully justified. 
If codling moth or apple-blossom weevil be present it is necessary to 
destroy their winter quarters as thoroughly as possible, and under 
such conditions the practice is warranted; but when spraying is 
employed merely to make the trees look nice, frequently more 
harm than good is done. 
Amongst the cleansing washes by far the most effective is 2 per 
cent, caustic soda. The older formulae included potassium carbonate, 
but subsequent experience has shown that it is of no particular 
advantage, merely adding to the expense without increasing the 
efficiency. 
Next to caustic soda in cleansing power comes lime wash. Unless 
trees are in a very rough state this is usually sufficient, and when 
it is used in spring against apple-sucker and aphis the trees never 
require any winter washing. 
At the bottom of the list comes lime-sulphur, though some growers 
contend that it has as great cleansing power as lime. It is sufficient 
to remove the green coat caused by the alga Pleurococcus, but not 
rough bark or thick moss. 
While cleansing washes have established their position as sprays 
to be applied during the dormant season, I venture to think and hope 
that a far greater field of usefulness exists for winter spraying. Of 
old we were told that winter spraying would kill insect eggs and 
fungus spores, and would act like a magic charm against all pests. 
Apparently no one took the trouble to make exact experiments to 
see whether eggs really were killed, or what was the effect of 
such winter spraying on them. Gradually, however, bitter experi- 
ence discredited the wild statements that had been circulated by 
makers of proprietary washes and others, and the contrary position 
was taken up that winter washes could not possibly kill winter 
eggs. 
Before discussing the question it would be as well to examine what 
advantages would accrue supposing the practice were possible. 
When considering the question of lime-spraying, it was found 
difficult to determine the exact time at which this should be done. 
If done too early some insects would hatch, if too late some would 
already have hatched. The winter, however, allows of many weeks 
when the work could be done. It may be objected that the weather 
is bad in winter and good in spring. As a general proposition that is 
undoubtedly true, but it must be remembered that spring spraying 
has to be done within a period of one or two weeks if possible, and 
effective work is usually limited to three or four at the utmost. How 
often spring weather is boisterous and windy, when spraying is well- 
nigh impossible ! In winter, however, spraying can be done any time 
from November to February, thus allowing a period of three or four 
VOL. XLII 4 Q 
