1907.] 



Potato Leaf-curl. 



469 



season will hold considerably more moisture than shallow, 

 badly cultivated land. In large cultures watering is not 

 practicable, but in special cases it might be worth while to 

 water previous to earthing. Earthing with the ground in a 

 dry and lumpy state is bad, because it surrounds the tubers 

 and plant with a medium from which moisture rapidly 

 evaporates. Growers should lose no opportunity of seizing 

 a favourable moment for earthing. Directly rain comes 

 the soil between the rows should be crumbled up and drawn 

 up to the plants. 



It is not clear that any special course of manuring can be 

 relied upon to exert much influence in checking curl. Certainly 

 the practice of spreading dry manure in the drills and placing 

 the sets in direct contact with it is to be deprecated. This 

 material does not retain moisture, and becomes like so much 

 hay round the plants. Manure from cowyards should be 

 used much more extensively than it is at the present time. 

 It is true that it does not come out very well under analysis, 

 but its mechanical value must be considered, and any want 

 of nourishing properties can be easily made up by the addition 

 of well chosen chemical fertilizers. Kainit has been found 

 of considerable value ; its caustic action is inimical to the 

 spores of the fungus, and the potash salts which it contains 

 stimulate the crop. Kainit is very cheap, and may be used 

 at the rate of 7 cwts. per acre towards the end of winter. 

 The application of Bordeaux mixture cannot be relied on to 

 check curl. 



The principal points connected with Potato Leaf-curl may 

 be stated thus : — 



1. The Disease. — (a) The disease is caused by the fungus, 

 Macrosporium solani ; (b) the base of the haulm is generally 

 the part first infected, but the fungus may establish itself in 

 the young sprouts ; (c) the mycelium spreads upwards in the 

 haulm, and downwards to the tuber, in which brownish streaks 

 may be found ; (d) the ascent of sap for the nourishment of 

 the plant is checked by the spread of the mycelium, and con- 

 sequently the plant becomes unhealthy ; (e) the disease may 

 be carried in the seed tuber, or spread by means of fungus 

 spores in the soil ; (/) at a later stage of the disease numerous 

 olive brown conidia form on the surface of the leaves, causing 

 dark patches. 



