The condition also is provided if the thickness of the crepe is excessive. In some factories, having no smooth-roll finishing machines, the crepes may have a distinct raised pattern upon them. It is usual to note that if “spot” disease appears in such crepes, it is incident to much greater degree in the thicker portions of the rubber—i.e., upon the raised pattern.
The direct connection between the rate of drying and the appearance of coloured spots or flushes is thus established, and it only remains to adopt precautionary measures which will lead to an avoidance of delay (1) between machining and hanging, (2) in drying.
It is indicated, therefore, that, if spot disease is to be avoided, the prime consideration is the preparation of a thin crepe which will dry quickly under average conditions. It may sometimes happen that even very thin crepes will sometimes be found affected on some estates. In such instances, it will be found that the design or situation of the drying-house is at fault, and that specially favourable conditions for the development of the fungi have been created by excessively wet weather. Should the trouble persist in spite of the preparation of the thinnest crepe, it would be advisable either to abandon this form of No. 1 product or to consider the installation of artificial aids to drying.
We have not yet encountered any case in which it was found necessary to treat the latex with an antiseptic or disinfectant substance for the prevention of “spot” disease. There appears to be an idea held in some quarters that sodium bisulphite may be so employed as a fungicide. This does not agree with our experience, which is confirmed by Sharpies (Bulletin No. 19, F.M.S. Department of Agriculture).
In 1913 experiments with chinosol were undertaken at the Pataling Laboratory of the Rubber Growers’ Association, and an account of the method of treatment was given in a printed report issued to subscribers. Dr. P. Arens,[20] of the Malang Experimental Station (Java), has also recommended the use of chinosol. The substance is expensive, but is effective in very small quantity. On the whole, given average conditions in factory practice, such aids should not be necessary, and where keen supervision is not available may lead to other difficulties.
[20] “Guide to the Preparation of Rubber,” Arens, 1918; Communications from the Experimental Station (Malang, Java).
It has already been remarked that it is possible for “spot” disease to develop in dry rubber which previously gave no evidence of the presence of fungi. The condition necessary to such an occurrence is supplied by the presence of moisture. Thus, to state instances which are by no means uncommon, if a box of rubber is allowed to remain exposed to rain, or is damaged by flood-water, or by sea-water during transit, or (sometimes) if the rubber is packed in a damp case, the crepe on arrival at its destination may be found to be affected to a degree dependent upon the extent of wetting and the duration of the wetting period.
No means are known by which these coloured spots, due to the growth of chromogenic organisms, can be removed from the rubber. Naturally, although they may be present in the darker lower grades of crepe, they are not so easily visible as in pale crepe. It follows, therefore, that every possible precautionary measure must be taken when pale crepe has to be prepared.
We are often asked whether it is possible for an infected piece of rubber to affect sound rubber hanging in the same building; and whether, in case of “spot” disease appearing, it is necessary to disinfect the drying-house.