174 



THE AGRICULTURAL NEWS. 



May 27. 1911. 



FUNGUS NOTES. 



ARROWROOT DISEASES. 



The following information on the subject of a disease 

 of arrowroot in St. Vincent is taken from a report by 

 Mr. F. W. South, B.A., Mycologist to this Department, sub- 

 mitted as a result of a recent visit to the island mentioned. 

 This visit was undertaken partly with the object of investi- 

 gating the disease under consideration. 



1. The fungoid disease known as the 'burning' of arrowroot 

 has been recognized in St Vincent for many years, and appears 

 to be of fairly wide distriliution. In patches here and there 

 in the field, the plants appear to have fewer leaves than the 

 healthy ones growing in their vicinit}-, while these leaves are 

 often rolled up and somewhat wilted. When such plants are 

 dug up, it is seen that the scale leaves of the rhizome are 

 blackened almost throughout. The disease penetrates to the 

 rhizome, and there forms small l)lack spots, which become 

 ■wider in extenr, and eventually cover most of its surface. On 

 cutting across such a diseased rhizome, it is seen that narrow, 

 dark-brown streaks, J-mm. wide, ran inward from the surface 

 in a radial direction for varying distances, which may be as 

 great as the complete radius of the section. These dark 

 lines originate from the black spots on the epidermis 

 of the plant stem. On examining carefully the outside of 

 the scale leaves, it is found in some instances that a brown 

 mycelium is present, running in narrow .strands along their 

 surfaces, while, under damp conditions, a white mycelium 

 may often be found between the surface of the creeping stems 

 and the inner surface of the scale leaves. The component 

 hypbae often occur in a small tuft springing from tjie black 

 spot on the surface of the rhizome, which marks the extremity 

 of one of the black lines mentioned above. 'Ihese oli.serva- 

 tions, and the fact that a white mycelium starting from 

 diseased plants was to l>e found in the soil itself, leave little 

 doubt that the disease is of a fungoid origin. 



M. The infected spots in the fields appear to extend but 

 slowly in the majority of cases — a fact which would seem to 

 be due to the comparatively slow growth of the fungus. 

 They vary in area from a few to several hundred square feet, 

 and appear to lie fairly constant in position from year to year. 

 I was informed that the symptoms of the disease did not 

 make themselves apparent in affected spots until the rhizomes 

 were nearly ripe for digging. Even were arrowroot the only 

 crop atl'ected by this disease, the matter would be of con- 

 siderable importance, as in some eases the number and extent 

 of the infected spots in a field are fairly large, so that a con- 

 siderable proportion of the crop obtained is diseased, and since 

 the fungus appears to affect the starch content, is rendered 

 practically useless. But there is another important feature 

 to be considered, which is that the host [ilants of this fungus 

 appear to be extremely numerous. Specimens were shown 

 me <if cassava, tannia and yam which were all diseased in 

 a similar manner and had been growing on ground known to 

 be infected. Indian corn, pigeon peas, plantains and coffee 

 are also said to be attacked, while I myself saw a similar 

 disease on bananas growing in a field in w^liich the arrowroot 

 in the neighbourhood was attacked by this disea.se, 

 and on cacao seedlings and bush jilants growing on the 

 borders of the same field, I am of the opinion that there 



can be very little doubt that all these host plants, 

 with the possible exception of coffee, were attacked by 

 the same disease. With regard to cotfee, I am not as 

 certain, as I was unable to examine any specimens. 

 I was, however, informed that the disea.se would attack this 

 plant, and avocado pear trees ;while it is worthy of record 

 that it has certain symptoms in common with the well known 

 West Indian root disease of cacao, which also attacks avocado 

 pear trees. No definite statement, however, can be made as 

 to the connexion between the arrowroot fungus and the root 

 disease of cacao until much further investigation has been 

 carried out. An illustration of the importance of the fact 

 that the arrowroot fungus can attack several host plants was 

 afforded me in the following information. A certain field of 

 arrowroot in which the attack of the fungus had become very 

 extensive was thrown out of cultivation and allowed to 

 remain in bush fallow for twenty-five years. At the end of 

 that time it was replanted in arrowroot. The resulting crop 

 contained, during the first year, a certain number of ' burnt ' 

 rhizomes occurring in patches; at the end of the second year 

 it had again become badly diseased. In this case, if the 

 fungus was continually present in the soil during the twenty- 

 five years, it probably continued its existence at the expense 

 of certain of the bush plants growing there. The only 

 alternative hypothesis is that the arrowroot used for replant- 

 ing was infected with the disease. The number of host plants 

 of. and the considerable extent of the damage caused by, 

 this fungus render it important that adequate measures for 

 its control should be undertaken on all estates where it is 

 known to cause damage. At the same time, the multiplica- 

 tion of host jilants renders the determination of such measures 

 a matter of considerable difficulty, which is increased by the 

 fact that the complete removal of arrowroot rhizomes from 

 infected soil is not easily accompli.>;hed. 



.3. The fungus causing the disease has, so far, not been 

 found to produce any definite fructifications. It is, however, 

 at present under cultivation at this laboratory, and it is hoped 

 that further information with regard to its life-history and 

 classification will be obtained in the course of a few months. 

 In the Kew Jiulletin of August 1893, No. SO, there is a short 

 report by the late Professor Marshall W'ard on some speci- 

 mens of this disease of arrowroot from St. Vincent which 

 were submitted to him by the Director of the Uoyal I'.otanic 

 (Jardens, Kew. In this report the fungus is referred to the 

 form genus Siiicaria, but no other fructifications were olitained 

 from which its systematic position could be more definitely 

 determined. 



4. As regards remedial measures, the following course 

 might be undertaken experimentally. Where the disease is 

 of a wide-spread nature, that is in fields where the infected 

 spots are both large and numerous, the whole field might be 

 isolated by a trench 3 feet deep and 2 feet wide. This trench 

 should be kejit open during all the operations to be described 

 below, in fact, until arrowroot is replanted. All the arrow- 

 root in the field should be dug up as thoroughly as possible, 

 and the diseased plants heaped up together: the field might 

 then be covered with bush, the trench mentioned above filled 

 with it, and the whole, includintr the diseased arrowroot, set on 

 fire, so as to [iroduce, if jiossible, sufficient heat to sterilize the 

 surface soil to the depth of a few inches. The field should 

 then lie thoroughly I'loughed or forked: the soil stirred thor- 

 oughly once a fortnight with a cultivator or with hoes: and 

 a crop of cotton planted. When the cotton h;is been harvested, 

 the plants, nu.\ed with a large amount of additional liusb, 

 should again be burnt, and the soil again ploughed or forked 

 and cultivated or hoed. A green diessing such as Bengal 



