XVI 



IRISH GARDENING 



Minimising the Loss caused by 

 Potato Disease. 



IN \i<'w oi" tlu' prevalence of potato disease llnsyeai', 

 a few siii^icostions nia\' be made with re_^fard to 

 keeping the loss as low as possible. The disease, 

 due to the fungus, Pliyloplilhora infcslans, is first 

 noticed, as a rule, on the leaves and haulms in the form 

 of dark spots or patches (surrounded very often by a 

 little ring oi white powder) which spread rapidly 

 ill a wet ov moist season ;ind soon destroy the whole 

 ^^i the phmt above ground. The life-history c^i the 

 disease has not been fully worked out, but it is almost 

 t'ertain that tubers are infected by the funj^us mycelium 

 making its way down the tissues o^ the haulm. 



The longer the tubers remiiin in the gromid the 

 greater is the danger of their becoming diseased, and, 

 .•is no growth of tubers can take place after the haulm 

 has died, the crop should be lifted as soon as the skin 

 will resist rubbing. The first efTect of disease on the 

 tubers is to cause the characteristic dark brow'n dis- 

 coloration of the flesh ; after the cells have been killed 

 by the fungus, bacteria secure a hold and bring about 

 the putrefaction and softening of the tissues, commonly 

 referred to as " wet rot." It is possible, too, that the 

 fungus (AVc/z'/n so/aiti, Per.s. ) causing Winter Rot more 

 easily attacks tubers affected by /'/•_)'/"/>/;//;(«•« than it 

 does healthy ones. 



When the crop is lilU'd it would bo highly tlesiralile, 

 if it were possible, to have all diseased tubers— even if 

 only "just touched" — separated from healthy ones, 

 but in most c^ses this is out of the question. Apart 

 from the pressure of work during the potato harvest, 

 the tubers in a bad se.ison such as the present are too 

 wet and dirty to jnakeit possible to distinguish between 

 the sound and the slightly affected. The difficultv can 

 be got over to a great extent, however, by the plan 

 adopted in some districts of placing the potatoes, as 

 they are raised, in small temporary " pits ' or " clamps," 

 covered simply with straw, and leaving them in these 

 until the pressure- of work is over, by which time the 

 tubers will have dried consiilerably. By sorting at ibis 

 later stage before placing in the more permanent pits, 

 there is not only less danger o( sound tubers becoming 

 infected in the pits, but a large bulk of slightly diseased 

 potatoes will be obtained quite suitable for immedi ite 

 use as food for stock, but which if left for even two 

 or three months would become quite rotten and useless. 



The construction of the pits or clamps has a good 

 deal to do with the proper keeping of the tubers. In 

 a wide, deep heap it is not easy for " steam " to escape, 

 and in the present season ilxvould be advisable to make 

 the pits exceptionally narrow. Needless to say, the 

 piece of ground selected as the site of the clamp should 

 be as dry as possible ; if it is not thorough' dry and 

 well drained, the floor of the clamp should be raised a 

 little above the level of the surrounding ground rather 

 than excavated even to the slight extent which is 

 common. 



The covering of the clamp is o( great importance. 

 In some parts oi the country it is the custom after 

 covering the heap of tubers with straw to earth it 



completely over at once. Such apian is decidedly bad. 

 aTid certainly conduces to extensive rotting in the pit. 

 Kven in a small clamp there is a certain amount of 

 " healing" probably chieflydue to the ordinary respira- 

 tion of the tubers, and " steam " or " sweat " is produced 

 particularly in the first few weeks. This heating can be 

 shown by direct measurement, or it might be deduced 

 from the fad that in ordinary circumstances potatoes 

 dry in the pit. If the "steam" is confined by a close 

 covering of soil, ide.al conditions for the rotting of the 

 tubers are secured. Ample facilities should, therefore, 

 be provided for the escape of the " steam " during the 

 first few weeks after storing ; perhaps the best plan is the 

 common one of leaving the ridge of the clamp covered 

 only with straw. If good straw has been used and pro- 

 perly laid on, no water will find its nay to the potatoes, 

 .'iiul a complete covering of soil nici)' be given before hard 

 frost is expected. Some potato growers, even in parts 

 of Scotland where severe frosts are experienced, leave 

 the ridge without soil throughout the winter, simply 

 putting on a layer of potato tops or of strawy manure 

 when frosts are anticipated. This is probably carrying 

 the principle further than necessary, and a better plan 

 is to cover the clamps completely with soil after a 

 month or so. leaving, at intervals of a few feet, ventilat- 

 ing shafts in the form of drain pipes or wisps of straw. 



With regard to the condition of the tubers when put 

 into the clamps, it is generalh- thought that they should 

 not be too clean, as a little soil or sand adhering to 

 lliem prevents them coming into too close contact and 

 so minimises "heating" and the spread of rot from 

 one tuber to another. In a season like the present one 

 there is little danger of the tubers being too clean, and 

 in m.iny cases they will be very wet and dirty. In such 

 c ises, and always when diseased tubers are present, 

 some growers adopt the plan of dusting a little lime 

 among the tubers. Kxperiments carried out by the 

 University of Leeds showed that when this was done 

 the potatoes came out of the clamps in spring "very 

 clean and bright," and though the lime did not prevent 

 a diseased tuber decaying, it did prevent rot spreading 

 from a bad tuber to those in contact with it. Ground 

 lime (/.(?., ground quick-lime) proved to be much better 

 for this piupose than slaked lime. It was found that 

 the use of the lime was attended with the disadvantage 

 that it seemed to encourage the early sprouting of the 

 tubers, but this may be regarded as a small matter 

 compared with the prevention of the spread of rot 

 through a clamp, and the sprinkling of ground lime in 

 the clamp at the rate of about i cwl. to every ton of 

 potatoes is confidently recommended. 



Flowers of sulphur, sprinkled over the tubers in the 

 clamp at the rate of 2lb. per ton of tubers, also destroys 

 the fungus causing Winter Rot, and holds in check 

 certain mites, woodlice, &c.. which may otherwise 

 convey the spores from one potato to another.— From 

 Tin- Jniiiital of the linart! of Ai^riciiltiiri'. 



ft^ e^* ^S 



A slxONl) edition of 'The Stoiy of my Rock 

 Garden " has just been published. It is similar to the 

 first with a few corrections, and is a useful book for 

 the amateur. 



