Yellow Blight of Potatoes. 



Yellow Blight of Potatoes. 



The Congested Districts Board for Ireland have prepared 

 information, for the use of their agricultural inspectors and 

 instructors, concerning the stalk disease [Peziza postuma) and 

 the root-rot fungus, which are associated with the appear- 

 ance of the "yellow"' blight of potato plants. 



It is stated that in many cases, more particularly in the 

 west of Ireland, the potato leaves turn yellow long before 

 the normal time when the plants die down ; in some kinds, 

 for instance, which should last till the end of September, the 

 leaves turn yellow or are quite gone at the end of July. 

 This early yellowing is a sign of disease, and plants with 

 such leaves do not give their full yield of tubers. 



On the underground parts of such plants fine branching 

 threads may be seen, particularly with a magnifying glass. 

 These threads are part of a fungus which attacks the plant 

 underground, both inside and outside, and prevents the 

 roots from doing their work — that of taking up from the soil 

 the water and mineral matter needed by the plant. The 

 fungus also attacks the roots of all kinds of weeds in the 

 potato plot, and in this way creeps more easily from a 

 diseased potato plant to a healthy one, and facilitates the 

 spread of the disease. 



The same potato plant with the yellow leaves and the root 

 fungus is often found suffering from the " stalk" disease, in 

 which the stem, either just above the ground or throughout 

 a large part of it, is no longer green, but white, dry, and 

 hollow. The decay of the stem causes it to topple over, and 

 a badly infected plot will at times appear as if the plants had 

 been trodden down. 



When the roots die, little black swellings — sclerotia — are 

 found on them, and similar swellings may also be found on 

 the leaves, stalks, or tubers. The decaying leaves often also 

 have little greyish-white tufts of easily detached spores, or 

 " conidia," upon them. These sclerotia serve to preserve the 

 fungus from one year to another, while the conidia also help 

 to spread the disease. 



The difficulty of stamping out the yellow blight is increased 



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