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THE AGRICULTURAL NEWS' 



Apktl 21, 1917. 



PLANT DISEASES. 



A SURVEY. OF THE YEAR 1916. 



Reports on the prevalence of plant diseases have now 

 come in from the Agricultural Officers in the chain of 

 islands from Tortcjla tn Grenada, and may usefully be 

 compared and suu]n)arLzed here They will eventually be 

 printed in full as usual in the West Indian Bulletin. 



I'LiMATK. Climate, of whirh the eftecti\f variable 

 components in this region are rainfall and wind, is ever 

 more clearly .seen to be the chief determining factor in the 

 incidence of the established diseases. Given the rainfall and 

 its distribution through the year, one might now with fair 

 accuracy deduce the extent of their occurrence under the 

 particular conditions of each island. 



During the year under review the rainfall on the whole 

 reached a good standard without being e.xcessive, but 

 abnormally heavy rains were general in October and Xovem- 

 ber. \n some of the islands, particularly in St. Vincent, 

 there was something like a deluge in that period. 



Heav)' winds were experienced in August, September 

 and October, associated with numerous cyclonic disturbances. 

 A section of Dominica on .\ugust 28, and the Virgin 

 Islands on October 9, were devastated by hurricanes. 



srii.AK-CANK. The only disea.«e of sugarcane now 

 occurring to any significant extent to these islands is the 

 root disease caused by Marasmius sacckari. The distri- 

 bution through the year of a sufficient supply of water to 

 maintain fairly regular gr^.vth led to a general freedom from 

 this disease. It may be gathered from the reports that in 

 this respect both 191.5 and 1916 have teen favourable much 

 beyond the average. Some instances of local damage are 

 reported from most of the iilands, which may be safely 

 assumed from previous experience to be due in most cases to 

 poverty of soil or insufficient f.ultivation. In Antigua there 

 is a probability that some of the trouble arose from the 

 •water-logging of very stitf soils. 



I'oi'i'ON. The cotton crop is extremely sensitive to 

 irregularities in the weather. The planting season adopted 

 lias been determined with refeieuce to the normal expectation 

 of a period of good growing weathei, in which the plant 

 builds up its leaf and branch .system, followed by a drier 

 period in which the bolls may maiurc without hindrance 

 from disease.s. The only couiplaint with regard to the first 

 period refers to the eftect of a dry .Tuue on the development 

 •of the plants on the windward side of Montserrat. The 

 early planting which exposed the pl.iats to this, later enabled 

 the cotton in that district to escape !he worst effects of the 

 unseasonable rains in ( )ctober and November. Fleavy lo.sses 

 from this cause were experienced in the remaining cotton- 

 growing areas, amounting in St. \ incent to little short of 

 disaster. So far as could lie ascertained the greatest part of 

 the damage during the actual wet piriod was due to the soft 

 rot fungus ( I'bytophtliora) which is very rapid and destructive 

 in its action This is definitely known to have been the 

 case in St. Vincent and Montseriat. The disease is dependent 

 on very moist conditiipns and in normal years is largely 

 confined to low growing, heavily -creened bolls. In the year 



under notice the writer found in St. Vincent that its spread 

 had been very largely arrested after about a week of fine 

 weather had succeeded the rainy period before mentioned. 



The bacterial boll disease was also generally prevalent 

 during the wet weather and so far as could be made out 

 always preceded the formation of the sunken spots infested 

 with a pink Colletotrichum which have been generally 

 accepted as evidence of the prevalence of anthracoose. 



The drier weather of the second half of November and 

 of December permitted of some recovery in the returns from 

 the latter end of the crop, and these are noted in St. Kitts 

 as being larger than was expected. In St. Vincent any 

 compensation of this kind was prevented by the prevalence 

 of the internal boll disease, which became quite general 

 with the large accumulation of cotton stainers usual 

 at the end of the season. This type of loss occurs in 

 the other islands to some extent and has been on occasion 

 severe, notably in Montserrat, but it is not yet clear why 

 its effects should be so generally serious in St. Vincent, while 

 in St. Kitts, for example, they are in comparison hardly felt. 



With regard to the year 1916 it may be said in general 

 that the early planted cottoii came off by far the best 



(.•.\CAO. The year was a generally favourable one for the 

 cacao crop. 



From St. Lucia there is a report of the prevalence of 

 fungoid disease having been increased as a result of over- 

 abundant rainfall. Pod rot and canker are generally distri- 

 buted to the cacao-growing islands, but do not with the 

 exception noted appear to have occurred to an unusual extent. 

 The Ro.sellinia root disease is too gradual in its .spread to 

 show any considerable fluctuation from year to year. 



As in the case of susar-cane root disea.se, to which it is 

 in its nature similar, the Diplodia die-back of cacao trees is 

 not much in evidence in a year of sufficient rainfall, and 

 some atfected areas show conHderable im|)rovement as a result 

 of favourable weather in this and the preceding year. 



LI.ME.S. From Dominica it is reported that in the 

 majority of cases steps are being taken to combat Rosellinia 

 disease in the plantations atfected. The red root disease has 

 been found in a district where it was not previously known, 

 the circumstances of its occurrence being such as to empha- 

 size the indications which already existed that insufficient 

 drainage is an important predisposing cause. 



The only disease of mature trees reported from St. Lucia 

 is a form of gummosis and collar rot associated with poorly 

 drained land. The prevalence of wet and cloudy weather 

 caused heavy losses of seedlings by damping off, and similar 

 trouble was experienced at times in Grenada and Montserrat. 

 Ill Dominica it was found possible to keep the disease in 

 control by prompt and repeated applic.itions of the usual 

 mixture of sulphur and lime. 



In Montserrat the dry weather of the month of .1 une 

 coming when the trees were maturing a heavy crop, caused the 

 fruit to be small and jjave the trees a severe set-back. The 

 generally ample rainfall of the years 101.5 and 1910 has not 

 arrested the progress of die-back in a declining field kept 

 under clo»e observation. 



With regard to miscellaneous crops thin- are few reports 

 of special trouble. Maize gave poor returns in St. Kitts, due 

 in one case noted to an undefined root disease. The leaf-rust 

 of ground nuts in Montserrat was more severe than usual, 

 and not so well controlled by Kordeaux mixture. In the 

 same island onions planted in September and ( >ctober were 

 a partial failure, a result which is not attributed to disease 

 but to the direct etiects of unsuitabk distribution of the 

 rainfall. 



W.N. 



