DIVISION OF BOTAXY 481 



SESSIONAL PAPER No. 16 



various farms; in wet land it is advisable to dig them earlier than on dry land; they 

 will also have to be dug at a later date when badly affected by blight, in order to 

 show the disease in the tubers, so that they may be removed, than if they were free 

 from it; but in general potatoes are ready for digging, under normal conditions, 

 when the stalks have died down and hence no longer take an active part in the manu- 

 facture of the reserve food which is stored in the tubers. Here it is where the 

 psychological moment may be missed, for there are potato diseases such as late 

 blight, early blight, rhizoctonia, or even the attacks of the flea beetle or potato bug, 

 which may cause the premature death of the stalks, and which may be mistaken for 

 their normal ' death.' Where these conditions prevail, the potatoes underground are 

 not ' ripe,' and, what is more important, there is no chance of their becoming ripe, 

 however long they are left in the soil. 



A ripe potato has all its cells well supplied with food material, i.e., starch, and 

 the skin adheres firmly to the tuber when the finger or thumb is applied to the 

 surface with a firm, rubbing movement. When the skin is easily detached during 

 this operation, the tubers are not ripe and should be left in the ground, providing 

 the tops are free from disease. It is an unfortunate fact, however, that the largest 

 percentage of potato fields are attacked by late blight and the stalks are killed 

 prematurely. In this case the tubers will also have become infected and are liable to 

 decay in the pit or cellar, unless certain precautions are exercised. 



The second fact favouring, and indeed inviting decay, is where potatoes are 

 lying too close to the surface of the ground in the field. Such tubers are easily touched 

 by frost, and, if not separated at once from those unaffected, they are sure to decay 

 when placed in storage. 



Another prominent source of rot in storage is the apparently unavoidable injuries 

 during harvesting of potatoes, especially when a potato digger is used. However 

 slightly a potato may appear to be damaged, as soon as the injury extends below the 

 skin, the tissues rich in available food are open to an invasion by 9cores of fungi and 

 bacteria, which find in such wounds a very suitable feeding ground. A large number 

 of such injured potatoes are picked up, notwithstanding every care, and are finally 

 deposited in the bins or pits. 



The above mentioned factors, involving more or less mechanical or physical 

 features, deserve, nevertheless, to be taken into careful consideration. The conditions 

 described on the potatoes themselves, which may be regarded as factors weakening 

 the power of resistance towards storage rots, and what is more, their exposure in their 

 impaired condition of ' health ' to the favourable conditions for the development of 

 bacteria and fungi which are ever present in bins, pits or the places of storage, should 

 certainly be regarded as the most prominent factors responsible for the largest amount 

 of losses occurring during storage. 



What is necessary to start into action the myriads of fungus spores and bacteria 

 present everywhere, and so destructive to stored vegetable matter of any kind ? Is it 

 not the moisture, warmth, absence of ventilation and light that encourage decay and 

 rot, and are not these conditions fairly constant in all pits,, bins, etc., where potatoes 

 are stored? Besides the excellent food in the potato is ready prepared for the use of 

 the ravenously feeding organisms of decay. Giving these lines a moment's thought 

 and consideration, will the majority of readers not own that these very conditions 

 prevail in their own cases? Have your potatoes been dug at tbe right time, were they 

 quite ripe? Were none touched by frost or damaged by the digger? Is your cellar or 

 pit well ventilated? If so, you have nothing to fear from storage rot, for then you 

 are no doubt awake to the necessity of preventing late blight and other diseases. But 

 those who must own up to one or more similar ' sins of omission ' had better turn to 

 their potatoes at once and start hand-picking them over, taking out all potatoes that 

 show any of these signs. 



16—31 



