400 



The Supplement to the Tropical Agriculturist 



points to Minachil taluk as tho locality of its first 

 appearance. The extension in this taluk has 

 been continuous from Erattupetta towards the 

 west. At the same time other outbreaks occur- 

 red in isolated places such as Alleppey. The 

 question of the infectious nature of the disease 

 is therefore of great importance 6ir.ce, if it 

 has succeeded in crossing the Vembanad Lake, 

 there appears to be no reason why it should 

 not eventually spread all along the Malabar 

 Coast. The disease is undoubtedly infectious. 

 All the evidence points that way. For instance 

 the steady gradual extension from east to west 

 in Minachil taluk can have no connection with 

 conditions of soil, climate or anything of that 

 sort ; it must imply the march of some infec- 

 tious matter. Similarly the small diseased area 

 at Alleppey is gradually extending but forms a 

 solid block, while to the north, east and west 

 there is none for miles. The best evidence, how- 

 ever, was got in a garden about half a mile south 

 cf the main area of disease at Alleppey. About 

 ten years ago a palm was purchased from 

 a garden in the latter area and transplanted into 

 this garden. It was diseased at the time but 

 the purchaser did not at once realise this fact. 

 None of his other trees were in any way un- 

 healthy at that date. Some few years after, how- 

 ever, the palm next the newcomer began to turn 

 yellow, and this was followed by others near by. 

 Now there are thirteen palms affected all near 

 together, while the original one has died and 

 been removed. It has not remained confined to 

 this garden but some five or sixothers adjoining 

 have each a few cases of disease. There can be no 

 possible doubt that the infection of this locality 

 was the direct result of introducing a diseased 

 tree and planting it amongst healthy cues, and 

 the owner himself firmly believes this. The 

 practice of transplanting palm trees is apparently 

 not rare. If a site has to he cleared for building 

 a house, the palms occupying it are 

 frequently sold by auction. Even large trees 

 are said to be purchased in this way, and are 

 removed with a mass of soil around the roots to a 

 new locality. Where a root disease exists 

 nothing could be more dangerous than this 

 practice, for the infectious matter is intro- 

 duced into healthy soil and gets a strong 

 footing there. How the disease has reached 

 palms situated at a distance from its original 

 starting-point, without affecting those in be- 

 tween, is not clear. There must be few parts 

 of India with a greater internal movement 

 of population than Travancore, judging from 

 the boat traffic on the backwaters, and into 

 Alleppey. It appears probable that the germs 

 of disease have been conveyed from place to 

 place by water either on raw coconut pro- 

 duce or in some other of the many conceiv- 

 able ways. It must be remembered that the 

 transport of . a small quantity of soil or a 

 few cocount roots from a diseased to a healthy 

 garden might readily lead to infection of tho 

 latte/. It appears probable that no other 

 means of spread exists than from root to 

 root through tho soil. Many fungus diseases 

 of plants are disseminated by spores blown 

 through the air. A well known instance of 

 this, in Travancore, is the coffee leaf disease. 

 Such blights are characterised by the rapid 

 way in which they spread over the whole of 



tho country where conditions favourable for 

 their existence occur. Every coffee-growing 

 part of South India was attacked in the few 

 years following 1869 when leaf-disease first 

 appeared. It is evident that the greater part of 

 North Travancore is suitable for the growth of 

 the cocount root parasite, since out breaks 

 have occurred in so many localities. Hence the 

 slow spread of the disease and the fact that 

 many parts of the coast belt have not yet been 

 affected suggest the absence of air-borne infec- 

 tion. The parasite has only been found on 

 roots below the soil level and, even if spores 

 are formed, they could not easily reach the air. 

 Extension through the soil, however, almost 

 certainly does occur and is practically the only 

 way in which the conditions described above as 

 found at Alleppey can be explained. The spread 

 of a fungus in the soil depends a good deal on 

 soil conditions. Cultivation hinders it, owing 

 to the disturbance and consequent aeration of 

 the upper layers of soil. Imperfect drainage is 

 frequently found to intensify root diseases, 

 probably both because scdden soils allow a more 

 active growth of the parasite and because root 

 development is less in such soils. Drought 

 probably injures both parasite and hostplant, 

 but the latter most, as its damaged root system 

 cannot cope with the demand for water unless 

 moisture is plentiful. In the dry season the 

 leaf symptoms in the Travancore palm disease 

 are at their worst but a severe drought, which 

 would probably cause a heavy mortality' in 

 diseased palms, is not likely to occur in North 

 Travancore. On the whole the evidence is that 

 heavy, ill-drained lands suffer most. In these, 

 especially in clay soils, the growth of the roots 

 is checked ; those that rot away are not readily 

 replaced by new ones ; the attempt is made, 

 but the new roots are feeble and unhealthy from 

 the start. The most difficult of all fungus disea- 

 ses to check are those which affect the roots of 

 plants. The parasite wh ch is the proba le 

 cause of coconut disease in Travancore enters 

 into the tissues of the living roots and is out of 

 the reach of any direct treatment. No ready 

 cure can. therefore, be looked for. Any appli- 

 cation which would kill the parasite must be 

 taken up by the roots ; with few exceptions 

 thess would also kill the roots and do more harm 

 than good. There are other methods however 

 by which we may hope to lessen its ravages and 

 these will be considered in order. 



1. The Eradication of tbe Disease bv 

 Destroying all Diseased Material and so 

 Preventing Infection of Healthy Palms. — 

 This is the method which is being employed in 

 the palm disease prevalent in the Godavari 

 district of the East Coast. In the latter, how- 

 ever, the limits of the disease are well defined 

 and are not very extensive. The disease itself 

 is confined to the " crown " and it this is cut off 

 and burnt, all infective matter can be destroyed. 

 In Travancore the disease is scattered through- 

 out a much larger area than in Godavari. Much 

 greater numbers of individual palms are 

 affected and, even were tho disease confined to 

 the crown of the tree, it would be a work of 

 great magnitude to attempt to eradicate it by 

 burning all diseased crowns. As in fact such 

 a meaeuse would bo useless unless the roots of 



