28 Potato Disease and Allied Diseases [ CH. 
more lime solution must be added. If the above 
directions are carefully followed the mixture will 
usually be satisfactory. 
The mixture is sprayed on the potato crop by means 
of a pumping apparatus to which a special nozzle is 
attached. For large areas a horse-drawn machine is 
necessary. For small areas the potatoes can be 
sprayed successfully by means of a “knapsack” sprayer 
which is carried on the back. 
The object of spraying the plant is not to cure 
the disease but to prevent it from spreading by 
covering all the parts liable to infection with a coating 
of a substance which will prevent the spores from 
germinating, or kill the delicate germ tube, and so 
keep it from penetrating the plant. It is no easy 
matter to cover the plant uniformly in the desired 
manner. The best results are obtained by means of 
a very fine spray, which on coming out of the nozzle 
hangs about in the air for a short time like a mist. 
Such a spray can only be obtained by means of suitable 
nozzles of which there are several useful forms on the 
market at the present time. A much finer spray is 
formed when a high pressure is obtained. 
Bordeaux mixture should be kept stirred while it is 
being applied to the plant and this should be brought 
about by an automatic stirrer inside the machine. 
With a coarse spray the mixture easily runs off the 
plants. 
About 80-90 gallons are required to spray an acre. 
The cost is about 6s. per acre, but varies with the 
distance of carting the water. The time to spray is 
just before the disease appears, i.e. the first and second 
weeks in July. In a bad season it is advisable to spray 
