THE POTATO i.\ BRITISH COLTMIUA. ' 73 



cover the susceptible parts of the plant with a coating of some material which will 

 kill the fungus before it can penetrate. This means that the fungicide must be on 

 the plants before the fungus, and that it must be renewed as it is washed off by 

 rain. New growth that is made after spraying is unprotected, and this is another 

 reason for repeating the applications. The spraying, to be effective, must completely 

 cover the susceptible surface. Obviously, if the spray only adheres in spots, there 

 is plenty of unprotected surface through which fungi may enter. The only test of 

 thorough spraying is to examine the plants afterwards and see that the spray mixture 

 is covering them, especially on the under-side of the leaves and in the centre of the 

 plant. It takes from 40 to 100 gallons of spray mixture to spray 1 acre of potatoes, 

 according to the size of the plants. A small patch o_f potatoes may be sprayed with 

 an ordinary barrel sprayer and hand-pump, connected with a line of hose, such as 

 is used by the small orchardists. For larger areas it is usual to employ a traction 

 sprayer (Fig. 77). In this case the power to drive the pump is furnished by gearing 

 with the wheels of the vehicle. The nozzles are so arranged that four or more rows 

 may be sprayed at the same time, the spraying being directed both from above and 

 from below, so as to cover both sides of the leaves. Such machines are made by 

 most of the makers of spray machinery (Fig. 78). 





Fig. 78. A four-row potato-sprayer. 



Whatever type of sprayer is used, it is important not to allow the spray material 

 to dry up inside the machine. After using, water should always be pumped through 

 it until it comes through clear. This will prevent much trouble from clogged valves 



and no/zles when the niaehine eomes t<> be used again. 



SPRAY MIXTURES. 



For spraying potatoes against fungous diseases a copper fungicide is always 

 n^ <!. Lime-sulphur, which is so extensively used in orchard- work has proved to be 

 injurious to potato-foliage, reducing the yield in consequence. On the other hand, 

 copper fungicides stimulate the foliage, so that the leaves become larger and darker 

 green and retain their vigour longer in the fall. In most cases the increased yield 

 1-n.nght about in this way in itself pays for the cost of spraying, apart from the 

 insurance against diseases. 



Bluestone or copper sulphate is the starling-point for the preparation of copper 

 fungicides. It cannot be used alone, since it is very injurious to foliage, producing 

 severe burning, even in weak solutions. It must therefore be combined with other 

 substances before using. 



