INSECTS AND DISEASES 51 
Finally, there are some diseases which arise 
from a lack of constitutional vigor in the plants, 
which, in turn, is commonly caused by poor care 
and failure to furnish some important food ma- 
terial. If such a condition seems present in 
your vines, you will have to study the situation 
a little and discover what is lacking in order to 
supply the necessary treatment. 
The sum and substance of the principles of 
spraying for insects and diseases is not difficult 
to understand. If something is the matter with 
your vines, study the nature of the trouble and 
the symptoms, and satisfy yourself that you 
know what insect or disease is at work. Then 
study its habits, its life history, determine just 
the treatment that is needed, then give that 
treatment comprehensively and thoroughly until 
the enemy is dissipated. 
But better even than this defence, efficient 
though it may be, are preventive measures. 
By means of these we prepare for the appear- 
ance of insects and diseases, and lie in wait for 
them, as it were, with fungicide and insecticide 
already on the plants. 
And yet, even that point of view is not the 
highest and best. Instead of fighting the pests, 
or expecting and getting all ready for their in- 
