398 



THE AGRICULTURAL NEWS. 



Decembkr It. 1913. 



PLANT DISEASES. 



ROOT DISEASE OF COCO-NUT PALMS 

 IN GRENADA. 



mycologist's eepoet. 

 The moat serious affection met with is that which is 

 destroying the trees at the Government plot at Westerhall. 

 It waa further met with on two estates visited and^ from 

 reports received may occur on several others. The Wester- 

 hJn plot consisted originally of something less than 100 

 trees well spaced out and planted on sloping stony land 

 with' a fair depth of medium loam on clay subsoil. Ihe 

 plot would have been the better for close draining when 

 the trees were planted, but there is no suggestion of actual 

 water-loecine and coco-nut trees not far away are mature and 

 thriving under conditions much less favourable in this respect 

 The ase of the trees is some five or six years and the growth 

 madp Ts very good. The trees not yet afJected by the disease 

 have an exceedingly healthy and vigorous appearance, and 

 those which are failing were e^ual to them in condition up to 

 the time when they be^an to show the symptoms of the disease. 

 The prrcess of failure is somewh a rapid, and its onset definite. 

 At Wenerliall it has taken etftct about the time when the 

 trees were beginning to bear. In another situation, however, 

 trees were dying before they had flowered, and in yet another 

 a'cer two or three bunches of nuts had been ripened. 



In no CHse could the occurrence of the disease be asso- 

 ciated with poor cultur..l conditions or with any lack of 

 vigour or any si^n of unheathiness whatever .apart from the 



diseate in question. . 



The symptoms of the disease, as they were conveniently 

 exhibited in all stages at Westerhall, are as follows: The 

 outermost, oldest leaf begins to turn yellow at the tip, and 

 the discoloration progresses until the whole leaf is 

 brown By this time the next leaf has begun to fail in 

 the "ame way, and thi.s iroces." continues until all the 

 expanded leaves have failed. In older trees examined 

 in another place the leaves which were first to fail, 

 tho.'Kh in all cases mature, were not alw^iys the oldest. It is 

 noteworthy that the leaves not yet reached in this process 

 preserve a healthy and vigorou.-^ appearance. When the 

 Bupport of the mature leaves is removed from the central 

 fioluoin of partially expanded leaves death is accelerated by 

 aecr.ndary causes. The unripened tissues are not usually 

 strong enough to support the weight of the column, and their 

 natural weakness may be increa.sed by the admission of palm 

 weevil There is further ihe tendency for the young tissues 

 near the bud of a failing tree to become involved in a putrid 

 bacterial rot This is not necessarily related to the specific 

 infectious bud rot which atUck. normal trees, and I saw no 

 sufficient evidence of the presence of this in the cases which 

 cam>- under my notice. What is observed la the bending 

 over of the top while it is still green, with a rapidly develop- 

 ing infestation of palm weevil in some cases, of a putrid rot 

 in others, and sometimes of both together. During the 

 proKiess of the dise&se there ia also very commonly a hrm 

 brown wet rot in large patches on the expended leaf bases, 

 and there may be aimilar smaller patchc.'i on the petiole 

 higher up. 



I regard the whole of the symptoms so far described as 

 secondary, consequent on the condition of the roots. Even 

 in trees which outwardly are just beginning to fail a large 

 proportion of the roots are already affected from without 

 inwards almost or quite to their points of attachment. The 

 coco nut root consists of a hard outer -shell and a central 

 woody strand, with pure white conical tissue of loose consis- 

 tency between. This cortical tissue appears to be the seat of 

 the trouble. While the woody central strand still appears 

 quite healthy the cortex becomes dry and tl^ky and passes 

 through stages of discoloration from white to light yellow, 

 then to dark yellow and brown; finally the root becomes 

 obviously dead and rotten. This condition is well advanced 

 before the failure of the top has progressed very far. 



When the stem of a tree in any stage of the di.ieise is 

 cut through, there is seen a well marked red ring "2 to .J inches 

 wide Ij'ing "2 to .3 inches from tlie exterior. It is of greater oi 

 lesser intensity, and extends in a well marked form to a greater 

 or lesser height in the trunk according to the stage the disease 

 haa reached. High up in trees with the central column of the 

 leaves intact the ring is resolved into separate reddened 

 strands in the soft stem an i in the petioles ofleives still 

 green and vigorous in appearance. 



In no case reported, so far, his recovery from this 

 disease ensued. There is no very definite evidence of its 

 communication from tree to tree, but in the cise of the 

 Westerhall plot appearances suggest that all the trees will 

 eventually be killed. Two other instances of plots in whiok 

 the affection appears likely to become general were seen; a 

 few cases were reported as appirenily isolated in their o:cur- 

 rence. 



The symptoms of the disease agree completely wii;h 

 those of the root disease of coco nuts prevalent in Trinidad and 

 Tobago, first described by F. A. Stockdale in IJOG, and 

 more closely investigated later by J. B. Rorer. (Stockdale, 

 Wes/ Indian Bulletin, Vol. I.\, pp. 362-Tl. liore- Circular 

 No. 4 Bd. of Agric-, Trinidad and Tobago, pp.2'(-33.) 



Rorer reports the result of an extensive niycological 

 examination, in which i9-t cultures were made from diseased 

 material, as having proved entirely negative so far as the 

 recognition of any causative organism is concerned. He may 

 be considered t" have shown convincingly that Stockdale's 

 idea of the caus.ition of the disea.se by the fungus Diplodia 

 is without foundation Rorers investigations, extending 

 over a period of two years, led him to the conclusion that 

 no fungus parasite is involved, and he was forced to regard 

 the disease as arising from unfavourable conditions in the 

 soil. What the.ie conditions are, 'whether it is the lack of 

 some element necessary to the continued growth of the 

 coconut tree, whether it is the pre.sence of some substance 

 which is toxic to coco-nut root.", or whether it is due to 

 acidity or lack of aeration in heavy soils it is difficult to say.' 

 A point he con.iiders worthy of note is that the disease is 

 fretiuently met with on old sugar land. 



It is difficult to reconcile the apparently sudden mani- 

 festation of the disease in trees which for five or six years 

 have grown with maximum vigour with any hypothesis of the 

 lack of an essential element from, or the presence of a toxic 

 substance in, the soil The definite and seemingly specific 

 characters of the disease are again.-tt the suggestion that ic is 

 due to the physical condition of the soil, since the ordinary 

 effects of poor aeration and heavy unfilled .soil are well 

 known to result in a general sickly appe»rance of the tree, 

 poor growth, and infestation with .scale insect.s. Moreover 



