386 



THE AGRICULTUKAL NEWS. 



Decembek 10, 1910. 



between the trees; or there is thealternatii-e practice of 

 growing a leguminous cover crop. For the latter pur- 

 pose, beggar weed (Besmodium sp.) is often sown. 

 This, it may be mentioned, is closely related to the 

 plants known as 'sweetheart' in the West Indies, which 

 are commonly found in pastures, where they produce 

 pods having D-shaped sections which stick tn the 

 clothes and coats of passing animals. 



The chief manures employed in citrus culture in 

 Florida are potash and pho.sphates, together with lime 

 when this is required, particularly for the purpose of 

 correcting acidity of the soil. Applications of nitro- 

 genous manures are only made sparingly since, as is 

 well known, the stimulation of the vegetative growth 

 of plants by such manures encourages the production 

 of inferiiir fruit known as 'ammoniated fruit", and 

 the plants make soft, sappy growth. The latter 

 circumstance is of much importance in relation to 

 attacks by white fly (Aleyrodes citri), as this pest 

 always appears to be most prevalent on plants exhibiting 

 a large amount of soft tissue in their growth. Par- 

 ticular significance is attached to the matter in Florida, 

 as white fly is the principal pest of citrus plants in 

 that State. 



The growing of weeds and cover crops in the 

 orchards is considered to be of much value by the 

 proprietors, especially because such plants aid in keep- 

 ing the air of the groves moist. It is in this way that 

 they aid indirectly in the control of the white fly and 

 scale insects, because the humid conditions that are 

 induced form the best medium fur tiie gniwth of the 

 parasitic fungi which keep these under control. This 

 is in addition to the use of such plants in affording 

 protection to the snil, cuver for insect enemies of the 

 pests, and in the case of the leguminous ]ilan:s, nitrogen 

 for the soil. 



A point of great difference between conditions in 

 Florida and those in the West Indies is the extent to 

 which the}- are favourable for spr.iying and fumigating, 

 in the first mentioned cotinlrv. This is why these 

 methods for controlling pests have been adopted there 

 to a considerable extent. It must not be forgotten, 

 however, that in many cases in Florida, the main 

 dependence fur the control of insect pests is placed on 

 their natural fungus enemies, because it is found that 

 the employment of this means is more satisfactory and 

 cheaper than spraying and fumigation. On occasions 

 when such control is for any reason found insufficient, 

 spraying materials are em^jloyed which are incapable 



of causing injury to the beneficent parasitic fungi, thus 

 giving these an opportunity to survive, and to become 

 effective once more in their special connexion. It 

 seems that a greater use might be made of this principle 

 of control in the West Indies. As regards the direct 

 use of the parasitic fungi as a means of keejjing insect 

 pests in check, this has become a matter of commercial 

 concern, and there are firms in existence whose chief 

 work is to keep in stock supplies of the useful fungi, and 

 actually to undertake the labour of disseminating the 

 spores throughout the orchards. Such a circumstance 

 is one of the best indications as to the practicability 

 of the employment of natural control of citrus pests on 

 a large scale. 



A final malter of interest is that experiments which 

 are being conducted with lime cultivation in Mont- 

 serrat (see West Indian Bulletin, Vol. XI, pp. 1 and 

 39), as well :is in other parts of the West Indies, indic- 

 ate that the methods to be used for the control of 

 pests and for cultivation by citrus growers in these 

 islands are likely to be very similar, with modifications in 

 accordance with the local conditions, to those that are 

 beine carried otit in Florida. 



SUGAR INDUSTRY. 



THE PREVENTION OF SCALING BY CAL- 

 CIUM SULPHATE, IN EVAPORATORS. 



The followinsr extracts dcalinir with this matter 

 are taken from Bulletin No. 33 of the Hawaiian Sugar 

 Planter;)' Association, in which work done in connexion 

 with the subject is described: — 



Two methods suggest themselves for correcting the 

 trouble clue to the formation of sulphate scale: the use of 

 barium salts or sodium carbonate in the juice during clarifica- 

 tion. The first reatment tremoves the sulphuric acid by 

 precipitation from the juice as sulphate of barium: but the 

 method is open to grave objections on account of the poison- 

 ous nature I'f the salts of barium and the danger of accident- 

 ally introducing them into products intended for human 

 consumption. The addition of sodium carbonate, in conjunc- 

 tion with lime, to a juice may be expected to have one of 

 t.vo actions. (1) If not enough lime is supplied to the juice to 

 produce an alkaline or neutral reaction, much of the phos- 

 pb(jric acid would not be removed, although there is sufficient 

 lime to combine with all the phosphoric acid remaining. 

 This is due partly to the solubility of phosphate of lime in 

 sugar and salt solution, but more largely to the increased 

 solubility of lime phosphate in an acid liquid. If to such 

 a liquid suthcient sodium carbonate is added to produce alkal- 

 inity, the lime phosphate would be largely or almost entirely 

 rendered insoluble and removed from the juice in the clarifier 

 settlings. {'2) If lime is added in sufficient quantity to pro- 



