T8 



THt AUKICULTUKAL NEWb. 



Makcii !i, 1918. 



PLANT DISEASES. 



PLANT DISEASES IN BARBADOS 

 IN 1916-17. 



The following account of observations made by Mr. J. 

 S. Dash, Assistant Suiierintendent in tlie Barbados Dejiart- 

 ment of Agriculture, is contained in the Annual l!f|">rtot 

 that Department, issued as a Supplement to the OiTidal 

 Ca:e/^e of January L'4, 1918. 



scGARCAXE. — During the j-ear tht- root fungus, 

 Jf'trismii/s Succ/iari was by far the most troublesome disease, 

 particularly in young ratoon cants. N[any instances of this 

 came under notice, especially in districts where very long 

 ratooning is practised. In the black soils, plant canes in 

 «ciiie fields also suffered from the disease. It is often thought 

 that this fungus is only a product of dry weather. As 

 a matter of fact any unfavourable environment will induce it. 

 In very wet seasons such as have been experienced in the 

 last two or three years, the disease frequently makes its 

 pre.sence felt in heavy fields which have not been sufficiently 

 drained. The yields of cane from such fields are often 

 considerably reduced and planters arc unable t" explain the 

 cause satisfactoril}-, yet m examination nf some of these 

 aoparently good fields during November and Dtcember will 

 reveal the presence of many hnles with few canes, and these 

 thin and ponrly developed. It is not necessary for the leaf- 

 sheaths to be all matted together for the disease to be 

 detected: at this stage there niay be hardly any cane to 

 reap at all. Good drainage, proper tillage, and the use of 

 healthy plants, in other words, conditions which keep up 

 the vitality df the plant, make the losses from root disease 

 very small in most seasons. 



C'l'UeiiitrichuKi /alcnium, the fungus causing red rot- 

 has been noticed in one or two i-olated instances. 



T/iie/(!i-io/-sis jiarndi'.iii, the fungus causing pine-ap|ile 

 disease, continues to be a veiy troublesome disease of cane 

 cuttings. The necessity of using good material for planting 

 and thoroughly disinfecting the cuttings with properly made 

 Bordeaux has been dwelt on over and over again in these 

 reports. 



The leaf-sheath red spot fungus, Cercosfiora rai/iuae, 

 has been fairly common during the season. 



The fungus Ctphalospor ni u aavrhnri, which was discov- 

 ered during the previous season attacking sugar cane, and with 

 which much work was done last year (Iteport 191.5-10), has 

 not appeared this year to any extent at the estate on which 

 most of the attack was noticed in 191 -"-Hi. It will be 

 remembered that the disease was noticeable only en canes 

 whose grfiwih had been interfered with in some way, being 

 most apparent on the outer rows of certain fields, which hud 

 suffered somewhat from the effects of a strong southerly gale. 

 A few examples of cane possessing this fungus have been 

 sent to the laboratory during the season from different places, 

 and isolated specimer>s have been observed in several c.me 

 field.s. In most of these cases Cephalosporium had followed 

 an attack of Mnrnfmius wcrhari, or had gained an entrance 

 through a borer hole. 



Ml>cKl.(/ANEf>l's. T-The writer knows of no instance 

 where cotton suffered much from any particular iliscase. 

 3lildew ;ind leaf (ipots are always prcfcnt in most cotton fields, 

 and there has been no reprirt or observation that these were 

 more prevalent than usual duiing the .season. 



Tfibacco is grown by one or two persons locally 1 'uring 

 the sea -on two diseases have come to the attention of the. 

 vriter One appears to be a bacterial disease causing a wilt 



of old plants by attacking them just above ground, a cankered 

 area from which there is much exudate being formed, which 

 gradually extends up the attm. The other is caused by 

 a fungus, a species of Fusarium, which has been found attack- 

 ing the roots of young plants and in many cases the bases 

 of the plants. The injury causes the young plants to wither 

 and finally die. The d-imping off fungi, Pijihiuiu sp. and 

 Rhi .iictonia sp.. were not present in this case. The recom- 

 mendations made for dealing with the former disease were 

 f rst, to pull up all plants showing the affection and to burn 

 them; then, if the trouble persisted, to grow some crop other 

 than tobacco on the soil for a few years, for the second 

 disease, the destruction of all dying plants was advocated, 

 this tc) be followed by a libernl ajiplication of Hme to 

 the soil, which should be given a rest for several months. 



THE CONTROL OF CACAO CANKER 

 IN JAVA. 



In a recent communication (Mofa/^e/i/io,-,, j;,„ /,,./ 

 Lahoi-ni drill in voor riaiifcnzifhtcii. No. .30), Dr. C. J. J. van 

 Hall reports the very striking success obtained on a certain 

 cacao plantation in Java by the adoption of a revised method 

 of general treatment for cacao canker. 



It must be borne in mind in considering the follo.ving 

 account that whereas in the West Indies, in Ceylon, and in 

 other cacao-growing areas the canker fungu.s, PlninpliHinnj 

 fiikri, is also responsible for heavy losses sustained from the 

 black rot of pods, and the passage of the fungus from pod to 

 cushion is held to be a fruitful source of cinker infection, 

 mycologists in Java, while confirming the common origin of 

 the two diseases, consistently report that pod rot, even on 

 estates badly infested with canker, causes but a very small 

 percentage of loss in that country. 



The cacao on the estate concerned in Dr. van Hall's 

 report is of the susceptible C'riollo type, and the trees 

 originally numbered some l)<,.'iOO on about 90 acres of land. 

 They were planted in 1901, and canker began to take effect 

 about seven years later. In the following four years, i.e. up 

 to the beginning of 1913, some 4,ii44 trees, no less than •2.'') 

 per cent, of the stanJ, succumbed to the disease. The 

 treatment applied iluring this period was adopted frf'Ui Ceylon 

 practice, and consisted in deep excision of the canker spots 

 until the discoloration was all removed, and covering the 

 wound with a mixture of carbolineum and black tar. 



The failure of this treatment, as demonstrated by thedeath of 

 about 1,00M trees in 191 J, led to a reconsideration of methods, 

 and the following measures were tested and recommended: 



(a) thorough pruning, in order to reduce the heavy canopy 

 previously maintained, and thus to admit more light anil air; 



(b) the mere shaving of the surface of the affected bark as 

 opposed to its complete excision, the idea being that 

 in conse(|uence of the close dependence of the fungus on 

 moisture, the exposure of the affected tissues wouUl dry 

 them out sufliciently to make them untenable by the 

 parasite; the treatment with tar was discontinued on 

 the grounds that it prevented effective supervi.-ion 

 of the work done, that it hindered the recognition of 

 recovery or relap.sc, and that the tarred layer prevented the 

 drying out desired; (c) the more careful control of boring 

 beetles, the tunneKs of which afford openings for infection. 



it was desired to add spraying of the trees with 

 Bordeaux mixture to these measures, but the <lilticulties 

 encounlert>d, esjjccially that of the provision of water, were 

 .so great that a decision was reached to test the effect of 

 the rest of the treatment without the spraying. 



