November 1, 1916.] 



THE INDIA RUBBER WORLD 



105 



Agricultural Society holds that thinning out should not be delayed 

 too long, but should be done early enough to allow the trees 

 ample opportunity to branch. 



The Experiment Station of the Ceylon Agricultural Society is 

 cutting out two small plots of Caslilloa rubber, having decided 

 that the space could be more usefully planted with other products. 

 A few specimen trees will, however, be retained. 



PLANTERS IN ARMY SERVICE. 



The "Malay Mail" of Kuala Lumpur, Federated Malay States, 

 as a supplement to its August 4 issue, publishes a "Roll of 

 Honor" containing a Hst of names of present or past residents 

 of the Malay States under British protection, who have lost 

 their lives in the present war. This is followed by a list of such 

 residents who have been, or shortly will be serving in the British 

 army. It will be noted that by far the majority of the names on 

 both lists are those of planters, or men in some way connected 

 with the planting industry. 



PROHIBITED EXPORTS FROM INDIA. 



A notification issued by the Department of Commerce and 

 Industry of India contains a revised list of articles, the exporta- 

 tion of which is at present prohibited from British India. Among 

 these articles appears rubber, raw and manufactured, which can- 

 not be exported to any destination except the United Kingdom, 

 France, Russia (except the Baltic ports), and British posses- 

 sions or protectorates. 



BARK ROT OF HEVEA IN BURMA. 



■"THE Department of Agriculture of Britisli Burma has pub- 

 •*■ lished a most interesting bulletin on "Blaclc Thread Disease 

 of Hevea in Burma," by I. F. Dastur, First .Assistant Imperial 

 Mycologist at Pusa, Burma. 



The "black thread disease" is what is commonly known in Cey- 

 lon as "bark rot," and has received repeated mention in The 

 India Rubber World. 



The naked tissues laid bare by tapping become disfigured and 

 damaged by the appearance of vertical, slightly depressed black 

 hues. These follow the tapping cut as it is continued down the 

 trunk of the tree and extend through the cambium into the wood. 

 The blackening of the tissues runs along the tapped area and 

 eventually covers the whole cut. Diseased areas soon become 

 vertically cracked, especially in wet weather. From the vertical 

 cracks latex occasionally exudes. In some cases there is a thick 

 wad of coagulated latex between the diseased renewing bark and 

 the wood ; in these cases the cambium is completely destroyed and 

 there is always a bulging out of the diseased renewing bark. This 

 soon decays, leaving behind a gaping wound, exposing the wood. 

 A true "canker" is thus formed. It is the damage to the cambium 

 which constitutes the most serious feature of the disease, for it is 

 upon the activity of this tissue that the tree depends for the 

 smooth and even regeneration of the bark cut away during 

 tapping. 



Careful inoculation experiments conducted by Mr. Dastur, with 

 pure cultures, have proved that this disease is caused by the same 

 fungus, a species of Phyloptlwra, which attacks fruits and causes 

 them to rot, and to which certain experts have attributed the 

 cause of abnormal leaf-fall. InoculaHon experiments on tapping 

 cuts, renewing bark and old bark showec" that the fungus was 

 capable of attacking the tree only through wounds. Inoculations 

 made on uninjured parts of the stem and branches invariably 

 failed, while those on the wounded surface were successful. 



The disease first makes its appearance soon after the rains set 

 in, and completely disappears after the close of the wet season. 

 Even during the monsoon, the progress of the disease is checked 

 during a long break. The annual fecurrence of the disease on 

 the stem has not been found to originate from the infected areas 



of the previous year, but has been observed to be due to fresh 

 infection. On an infected area the disease spreads downward, 

 following the tapping cut ; if tapping is stopped the spreading of 

 the disease is stopped. This is what would be expected from the 

 discovery that the trouble is caused by a parasitic fungus. The 

 fungus, however, lies dormant when tapping is stopped during 

 the monsoon, and resumes its activity when tapping is recom- 

 menced any time during the rainy period. 



The fungus spreads most rapidly in wet weather, and it is 

 pointed out that closely planted trees, which create a dark, moist 

 atmosphere, favor the disease. This leads the author to suggest 

 that one of the best methods of control is to thin out the trees 

 so as to let in more light and air. The application of fungicides,, 

 like Burgundy Mixture, was a failure, though a 20 per cent solu- 

 tion of carbolinium is said to have been a success in Java. Cessa- 

 tion of tai)ping at the first appearance of the disease, and collec- 

 tion and destruction of all diseased fruits, are recommended by 

 the author as practical means of control. The latter is, however, 

 a difficult procedure in rubber estate practice and requires much 

 labor. 



Commenting on this report, the "Planters' Chronicle" says that in 

 South India it has been found that a combination of cessation of 

 tapping on attacked trees, with the application of a thin smear of 

 a mixture of tar and tallow applied to the diseased spot, has 

 proved very effective. The mixture is applied with the finger and 

 then rubbed with a small piece of gunny cloth, so as to confine 

 the smear to the bark area attacked. Its action appears to be 

 twofold. The tar acts as an antiseptic, while the tallow forms a 

 waterproof covering, and thus deprives the fungus of the moist- 

 ure so necessary for its growth and welfare. Afier the monsoon, 

 the treated areas gradually shed a thin scale of tar-coated bark 

 and expose a clean, healthy surface beneath. 



Covering the tapped surface with a mixture of cowdung, clay 

 and sulphur has also been found beneficial ; the bark renews 

 quickly and well enough beneath this coveiing, and the bark rot 

 is reduced. The mixture may be best made by boiling one ounce 

 of sulphur in half a kerosene tin of water and adding equal parts 

 of clay and cowdung till a thick paste is obtained. The addition 

 of a pinch of salt tends to keep the mixture moist and to prevent 

 it from cracking, after application. This mixture is chiefly applied 

 in the dry weather. It prevents the tapped area drying out and 

 promotes good bark renewal. It appears also to have a beneficial 

 effect, as far as bark rot is concerned, when the rains begin. In 

 Ceylon the mixture is applied each month, within a quarter of an 

 inch of the tapping cut, but in South India it is usually applied 

 over the tapped area when tapping ceases, as it does in some dis- 

 tricts, on account of the dry weather. 



It is interesting to note that the mycologist in Burma has been 

 successful in inoculating healthy trees with the disease, whereas, 

 in Ceylon, experiments undertaken by the Ceylon Committee of 

 Agricultural Experiments did not show the same result. Work- 

 ing on this disease in Ceylon. Mr. Bryce was inclined to attrilnite 

 it to a physiological effect, and not to fun.gus disease at all. Mr. 

 Bryce failed in his attempts to inoculate trees with the disease, 

 and his theory was, apparently, that in wet weather the formation 

 of the cork layer which protects the cells of the inner tissue, and 

 of the wood cambium, was delayed. This causes cells to die 

 locally, and the decomposition products thus set free infiltrate 

 into the neighboring cells and kill them. It may be that the black 

 thread disease in Burma is different in nature from the "bark rot" 

 disease of Ceylon plantation !Ie~ra: however, Mr. Dastur is to 

 l>e congratulated for having definitely proved this disease in 

 Burma to be due to the presence of a fungus, as the first real 

 step towards the control of plant disease is to discover to what 

 it is due. 



The I.si.and of Hainan, China, Will Soon Need Rudber 

 machinery in order to bring its plantation product up to the 

 standard qualities in the Singapore market. 



