286 



THE AGRICULTUBAL NEWS. 



September 8, 1917. 



PLANT DISEASES. 



SERIOUS NEW CANE DISEASE 

 PORTO RICO. 



IN 



The Louisiana Flanter dated August 4 published an 

 account bv Mr. John L. Stevenson, Pathologist of the 

 Insular Experiment Station, of a cane disease which has 

 appeared in the north-western quarter of Porto Pdcn, and 

 has been observed for at least three seasons to be spreading 

 steadily. 



It occurs at present in a district some 40 to 50 

 miles across, mostly in fields among the foothills and in the 

 river valleys. Many fields have already had to be abandoned 

 so far as cane growing is concerned. The coastal plain i.s 

 practically free as yet. 



SYMPTOMS. 



'The one marked and constant symptom of the disease, 

 and the one by which it is easily recognized by anyone who 

 has occasion to visit diseased field.", is the peculiar mottling of 

 the leave.".' This feature is described as differing distinctly 

 from the familar chlorosis, (known variously in the 

 West Indies as moonshine, saltpetre, or gall patches). 'In 

 the case of the disease under discussion the leaves are marked 

 with numerous white or yellow spots and stripes with irregu- 

 lar, indefinite margins These are generallj- much longer 

 than broad, and while in initial cases they may be few 

 in number, they are generally so numerous as to occupy in 

 the aggregate a large portion of the leaf surface. In newly 

 attacked stools the leaf surface forming the back-ground 

 may be dark green, but as a general rule it becomes a light 

 abnormal green or yellowish-green, so that a sick field is 

 noticeable from a distance because of its light colouring.' 



Affected stools may be dwarfed, but others are to all 

 appearances normal except for the mottling described, and 

 this may occur on one, several, or all the stalks of a stool. 

 Plants from the apparently healthy canes of a partially 

 affected stool all give rise to mottled shoots. 



In the advanced stages of the disease, in ratoons which 

 have become very much stunted, a constant character is the 

 appearance of discoloured areas on the stalks. These are 

 grej- or dirty white in colour, and may be so abundant as 

 almost to cover the surface of the internodes. They become 

 slightly sunken, but do not penetrate deeply into the tissues. 



TItANSMISSIOX. 



It has been found that cuttings from affected canes- 

 invariably reproduce the disease, no matter how they are- 

 treated or in what soil they are planted. The disease, once 

 it has appeared, is cumulative in the successive crops of 

 ratoons. It is not Stated that the soil retains the infection, 

 but it appears from the spread of the disease, and from the 

 information that some of the seedling and foreign varieties 

 brought in for trial from other districts have been attacked, 

 that there is son-e means of transmission other than descent 

 from affected stools or affected strains. 



SUSCEPTIBILITY OF VAEIETIES. 



From the first, the Otaheite (Bourbon) cane has beet* 

 especially susceptible, and the elimination of at least that strain 

 of it which is grown in the infected district seems certain. 

 Other native white varieties are attacked. A striped cane 

 which last year appeired lo be somewhat resistent has in 

 many sections proved as weak as the Bourbon. A dark-red 

 cane of which much had been hoped has also shown evidence 

 of succumbing. As mentioned above, seedling and foreign 

 canes have been introduced from other districts. In some 

 instances they have been readily attacked, in others the out>- 

 come is still doubtful. 



The measures which have proved successful in dealing 

 with other cane di.seases: 'increased fertilization, liming, very 

 thorough preparation of the soil, most careful selection of 

 disease free seed, treatment with B )rdeaux mixture, use of 

 new land, introduction of new varieties or of seed of new- 

 strains of old varieties brought from outside districts; all 

 these and other methods as well have been tried, either 

 singly or in combination, without uniform results other than 

 that the disease has continued to gain ground.' 



In the main, concludes the writer, it will be advisable 

 for a few seasons at least to substitute some other crop for 

 sugar-cane on the fields in which the disease has become 

 prevalent. A rotation of crops which would include a legume, 

 food crops, and then cane is suggested as the ideal system 

 for the infected region. Reference is also made to the 

 possibility of establishing the larger fodder grasses and 

 reviving the industry of cattle-raising. 



Some remark.^ on the analogies between this and 

 certain other much discussed diseases will appear in a sub- 

 sequent issue of thi- .lournal 



WN. 



The losses in advanced cases of infestation extend to 

 the complete failure of the crop, in others to reduced yields in 

 all degrees, according to the proportion of stunted stools and 

 rotted stalks. The affected canes have a tendency to be pithy, 

 and poor in juice, and the behaviour of the juice is liable 

 to cause a great deal of trouble in the factory. As a conse- 

 quence, the various centrals refuse to receive cane which 

 shows evidence of the disea.se. 



None of the many 

 of the disease has been 

 in experiments, nor has 

 infectious when injected 

 to the present comjiletel 

 be due to any parasite. 

 Serch disease if the Eas 

 respcct.«, but with which 



tALfS.VTION. 



fungi encountered during the study 



found to be capable of initiating it 



the juice of diseased canes proved 



into healthy canes. Its cause is up 



y unknown, but it is believed not to 



A coni[)arison is suggested with the 



t Ii.dies, which it resembles in many 



it does not correspond in detail. 



AGRICULTURE IN BARBADOS. 



.July and August 1917, have been just the reverse of 

 these months for the year 1916. In .Tuly 191G there was 

 a shortage of rain, and August of that year was a very heavy 

 month during which over 12 inches was registered. This- 

 year the rainfall f<ir July was considerable, while during 

 August there have been spells of showerless days. 



The past fortnight has been one of activity in connexion 

 with the putting out of farmyard manure. Everywhere 

 carts uuy have been seen laden with thii valuable article. 

 In some instances it is being applied direct to the fields, in 

 others it has been put on the pens now in process of formation, 

 to be distributed at a later date. On several sides we have 

 heard planters sjjeak of the backward condition of their 

 manure supply, a.s compared with that of some previous years. 

 We regret to hear this, as a good supply of manure, and 

 especially of farm y;ird manure, is indispensable to agricul- 

 tural prosperity. At this period last year there was similar 



