?38 



THE AGKICULTUKAL NEWS. 



Jllv 



1918. 



PLANT DISEASES. 



BOLLS 



INTERNAL DISEASE OF COTTON 

 IN THE WEST INDIES. 

 In the recently issued number of the //V>7 huhan 



JiuUithi (Vol. -WII, No. 1), there appears a paper on the 

 above subject by Mr. W. Nowell, D.I.C , Mycologist on the 

 ^taff of th«> Imperial Department of Agriculture 



In a previous paper in the Wat Indian Bulletin 

 <Vol XVI No 3), the writer has shown that in the AVest 

 Indies the' staining of developed cotton lint takes place in 

 the green unopened boll, and with the exception of a varying 

 proportion due to external boll disease, is principally caused 

 by direct infection of the lint with specific fungi, of which 

 four species have been found, or, more rarely, with bacteria. 

 ?uch infection was shown to take place, without apparent 

 e.vception, through bug punctures, mainly made, under pre- 

 vailing circumstances, by the cotton stainers {Dysdoxiis spp.). 

 The present paper discusses (<() the part taken by other 

 bugs, especially the green bug {iW-.ara viridula), in injuring 

 and infecting bolls, (/■) the nature and significance of direct 

 bug injuries which are not infected, and further, (,) records 

 the occurrence of the fungi of internal boll disease in the 

 seeds of numerous plants other than cotton- 



The observations and experiments recorded were m_ade 

 during a visit of seven weeks' duration, from October 17 to 

 December 9, 1917, to the island of St. Vincent. 



The methods of study adopted included (<;) field obser- 

 vations of the relation between the prevalence of bugs and 

 the amount of shedding, boll injury, and infection occurring; 

 (/.) close examination and record, lock by lock, of parcels of 

 fresh green bolls obtained from selected typical districts; (.) a 

 .series of experiments in which bugs of various species, from 

 tnowD sources, were confined in cambric bags on uninjured 

 bolls of known age; (,/) examination for infection of fruits of 

 the wild and cultivated host plants of bugs; (< ) attempts by 

 means of direct examination, dissections, and cultures to 

 elucidate the carriage of infection by the bugs concerned. 



The conditions relating to the occurrence of bugs in the 

 field are separately discussed by the Entomologist in another 

 paper of the same Bulletin. The commonest speciis, Ac-.am 

 riridulij and Edeim medital'iinda, known collectively in St. 

 "Vincent as bu.sh bugs, have a wide range of hosts, but are 

 most commonly found associated with leguminoiis plants, the 

 latter especially y,'\t\i Cijanns india/s, the pigeon pea. On 

 the estates most infested with the.se bugs there were heavy 

 losses from the shedding or drying up of small bolls, and 

 from direct bug injury. There was also a variable but 

 rather low percentage of infecti-jn with internal boll disease 

 The following is a summary of the palmer first mentioned, 

 which is the outcome of careful' experimental investigation. 



Thesucce-'s of the control measures adopted against the 

 cotton stainer in that island was found to have reduced the 

 prevalence of the disease to negligible proportions ..ver large 



areai>. , , . , 



Severe infestations with the green bug ami tlie pea clunk 

 occurred in some localitie.^ and the resulting damage to 

 cotton bolls afforded the principal subject of study. 



Clo.se attention was given to the direct effect of bug 

 punctures on the boll.", and it was found, in regard to the 

 green bug especially, that the resulting injury to the develop- 

 ing seeds prevents or stops the development of the lint, 

 causes the shtdding or drying up of young bolls, and is in 

 both ways the .'ource of heavy losses. Punctures made by 

 cotton .t:.ii.(r:. and the leaf- footed bug liave similar effects. 



The losses brought about by direct injury are for the 

 most part complete, and are additional to those caused by 

 the staining of developed lint due to internal boll disease. 

 The amount of injury of the latter nature was found to be- 

 notably less in the case of green bug than of stainer infesta- 

 tion. . 



The direct injury resulting from infestation with the pea 

 think was small in amount, and consisted of stained spots on 

 the surface of the lint, occurring immediately below some of 

 the small proportion of punctures which appeared to pene- 

 trate the wall of the boll. No injury to the seeds was 

 observed in connexion with this bug, and no case of infec- 

 tion with internal boll disease. 



A series of experiments is recorded illustrating the effect 

 of confining bugs from known food-plants on previously 

 protected bolls of known age. Evidence was obtained that 

 the punctures of the green bug readily bring about infection 

 with the fungi of internal boll disea.se, but only when the bugs 

 are transferred from infected plants. No infection was pro- 

 duced even in the latter case by the pea chink. 



SISAL CULTIVATION IN EAST AFRICA. 



The third of a series of articles appeared in Tropiail 

 Life, March 1918, consisting of notes by Mr. E. H. Heron, 

 Director of Agriculture of the Mozambique Company. The 

 author bases his opinions upon experience of sisal cultiva- 

 tion in Portuguese East Africa and on the Zambesi Itiver dur- 

 ing the last nine years. The total area under sisal in these 

 districts is between 19,000 and 20,000 acres of different 

 classes of soil on plantations which are practically at sea- 

 k-vel, the highest altitude not being more than 400 feet. 



The life of the sisal plant in East Africa is put by 

 Mr. Heron at six and a half years, and rarely seven. The 

 plant reaches maturity in the third year, thus allowing 

 leaves to be cut for nearly four years, before 'poling' and the 

 consequent death of the plant take place. 



It must be remembered that the sisal plant is propaga- 

 ted either by bulbils, which are produced on the branches of 

 the flowering pole, or by suckers, which arise around the 

 parent plant from the underground rhizome. Mr. Heron 

 devotes much of his article to the consideration of which of 

 these two methods of propagation is the more advantageous. 

 In reckoning the period of growth of the sisal plant, 

 Mr. Heron only takes into consideration plants grown on 

 suitable soil, and where the cultivation is conducted in a 

 proper way during the whole life time of the plants. He 

 remarks that any neglect in the cleaning and cultivation, 

 even when the plants are in good soil and under excellent 

 climatic conditions, causes them to pole irregularly, and 

 before their proper time. , , , j 



With the exception of a few experjmental patches planted 

 from suckers, the whole area under sisal in the district has 

 now been planted from bulbils. 



Mr. Heron in .summing up the advantages and disa.l- 

 vantages of this method of propagation, states that the advan- 

 tages of bulbils are as follows:— 



(1) They can be selected from vigorous plants that- 

 have all poled at the. proper time. 



(2) They arc all about the same age and size. 



(3) They can be planted out in large numbers in the 

 nurseries at the same time. 



(4) The collection of bulMl- is '-lieap, rnvtiiig only a 

 few pence per thousand. 



