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THE AOIUCULTUUAL NEWfc> 



March 30, 1912. 



FUNGUS NOTES. 



BUD ROT OF THE COCOA-NUT PALM. 



-'uPaet II. 



In the last number of the Agricultural A'ews, some 

 information was given as to the symptoms, distribution and 

 cause of cocoa-nut bud rot, as recently described by J. P.. 

 Johnston in Bulletin No. 228 of the Bureau of Plant Indus- 

 try of the United States Department of Agriculture. In the 

 present article, a further account, dealing with the method of 

 spread and treatment of the disease, is given, the subject- 

 matter being taken from the same source. 



SPREAD OF INFECTION. The actual means by which the 

 infection is spread from tree to tree is as yet not determined 

 with absolute certainty. Two agencies have been suggested, 

 namely wind and insects. There are two important arguments 

 against the theory of wiiid distribution. The first is the spor- 

 adic nature of the attacks in any locality, combined with the 

 fa(^t that the disease appears to spread against or across the 

 direction of the prevailing wind, as frequently a.s it spreads 

 with it. The second depends on the nature of the disease it- 

 self. Since the infected tissues are deep-seated in the crown of 

 the tree, and are enfolded by the firm leaf bases, it is difBcult 

 to see how pieces of this moist tissue could be distributed by 

 the wind. In another way, the nature of the causative 

 bacteria is such as to render it unlikely that they can survive 

 such desiccation as would be necessary if they are distributed 

 by the wind as a light dust. 



On the other hand, nearly all observers have recorded 

 the presence of numerous insects in the decaying tissues of 

 the bud. In the tops of the trees a great variety of forms 

 may be found, while in the diseased tissues those predomi- 

 nating are the larvae of flies, often scavengers, and of earwigs. 

 These insects might spread the infection, either by means of 

 small portions of decaying tissue adhering to their bodies, or 

 through their excreta, in which living individuals of the 

 causative bacteria might be contained. .Johnston was able to 

 obtain certain bacteria which gave reactions typical of Bacillus 

 (oli, from the intestines of earwigs found in diseased trees 

 in Cuba. 



Another animal that may be responsible for spreading 

 infection is the turkey buzzard, which may be commonly seen 

 in diseased trees, and is stated to be found in all tropical 

 countries where the bud rot occurs. The diseased tissues, as 

 is well known, have a very unpleasant odour, and it is likely 

 that the birds are attracted by it; in conne.xion with this, 

 Johnston notes a statement of Dr. Smith: 'that twice, at 

 Baracoa, buzzards swooped down on the rotted hearts of 

 palms he had laid aside for study, and would have carried 

 the material oft", if he had not made a frantic rush to protect 

 it.' Although the fact that these birds feed on the diseased 

 tissue has not been definitely proved, yet Johnston was able 

 to obtain from their excreta a few colonies of bacteria 

 giving reactions very similar to those of the bud rot organ- 

 ism. He also notes that, in Porto Rico, where the disease 

 probably does not exist, turkey buzzards are either very rare 

 or absent. Although the actual carrier, or carriers, of the 

 disease has not been definitely ascertained yet there is con- 

 siderable evidence that certain animal agencies are respon- 

 sible, particularly insects and turkey buzzards, while the 

 evidence in the case of other causes is of a negative 

 character. 



TREATMENT. Johuston thought at first that bud rot 

 almost always commences in the central leaves, but careful 



investigation showed that in many cases trees could be found 

 with healthy central leaves, while the spikes, or more com- 

 monly the swords just opening, revealed brown water-soaked 

 discoloured areas: in some cases also the bases of the lower 

 leaves were diseased in the same way. Trees showing these 

 discolorations alniost always developed a soft rot of the 

 terminal bud, at a later date. It was, however, hoped that 

 careful removal of the infected leaves, flower spikes and 

 swords would result in the recovery of the tree, at any rate 

 if sufficient of the suspected parts was pruned. Twenty-one 

 trees were treated in this way, but though they remained 

 undiseased at the centre for three months, they all eventu- 

 ally succumbed. 



As there has been a belief that certain disinfectants are 

 capable of checking the disease, applications of salt, copper 

 sulphate and Paris green were made to trees infected as 

 above in which the central leaves were quite healthy. In 

 every case, it was found that the treatment was without 

 eflfect and that the disease progressed at about the same rate 

 and killed the trees in about the same time as it did in the 

 case of untreated trees in the neighbourhood. 



Another remedial measure from which successful results 

 have been anticipated is flaming. Johnston considered that 

 it was unlikely to have any practical value owing to the 

 arrangement of the leaves and also to the failure of other 

 methods of external treatment ; consequently he did not 

 experiment with it himself, but an examination of trials 

 conducted by others fully confirmed his opinion of its ineffec- 

 tiveness. He sums up the whole position with regard to 

 flaming as follows : — 



' From the arrangement of the crown it is impossible 

 for the heat to penetrate into the inner tissues in sufficient 

 degree to dry out the diseased portion without seriously 

 aflfecting the growing part of the crown. Any flaming what- 

 ever will destroy the lower leaves and all the nuts, so that 

 even if the tree is not killed, at least a year's crop is des- 

 troyed. The scorching of the leaves and the charring of the 

 trunk so kill the superficial tissues as to permit the rain to 

 soak in and a subsequent rot to take place. It has been 

 contended by some people applying this treatment to their 

 trees that there was subsequent recovery from the disease, 

 at least to the extent of flower spikes opening out and setting 

 nuts. It should be noted, however, that the tree, while 

 retaining the disease, may send forth new flower spikes and 

 nuts for a period of at least a year after infection has taken 

 place without any treatment having been applied. The 

 writer possesses records of individual trees which .show this. 

 In many trees flamed the disease progressed subsequently so 

 that it presented to the writer no evidence of the value of 

 this treatment. As a diseased tree is certain to die if not 

 treated, there can be no error in flaming it ; but to iiy this 

 method with healthy trees in the expectation of w-arding off 

 infection is not advisable, because ( 1 ) there is no evidence that 

 the treatment would succeed, and (2) there is the certainty 

 that the tree would be seriously injured in a way that would 

 make it more susceptible to infection." 



Although none of the remedial measures tried have 

 proved ett'ective in preventing the progress of the disease in 

 infected trees, yet adequate preventive measures will check its 

 general spread and reduce to a minimum the number of annual 

 cases. The first .step is to destroy all the sources of infec- 

 tion ; the second to destroy or reduce in numbers its means of 

 transmission ; and the third to do away with conditions 

 favourable to its development. In regard to the first step, 

 the tops of all infected trees must be cut oflF and destroyed. 

 Johnston recommends that when only a few trees have to be 

 destroyed the best plan is to cut oiT their tops and liurn them, 



