378 



The Supplement to the Tropical Agriculturist 



CHIEF OF THESE SECONDARY FUNGI 



forms black patches on the bark of Hevea. If 

 you cut down a tree and leave it for a week or 

 so, it gets covered with this fungus. In the case 

 of the branch killed by " die back " this black 

 fungus (Diplodia) settles down and kills the rest 

 of the tree. That makes it difficult to tell when 

 you send us the top of a tree, all the way to 

 Peradeniya, whether it had died of " die back'' 

 or root disease, as it gets affected with this 

 secondary growth of fungi. If you do not send 

 the whole tree, it is practically impossible to tell 

 what disease has affected any particular portion 

 because by the time the branch or section gets 

 to Peradeniya it has got a host of Diplodia. You 

 will find that between the bark and wood is 

 black as coal. If you scrape the bark a little, 

 you will find black spots which are full of 

 spores. The best way to deal with "die back" 

 is to cut off the branch before the tree is killed 

 right off to the base. The dead top and green 

 lower branches are absolutely distinctive. There 

 has been rather an outcry in other districts, not 

 much in the Kelani Valley, that all the trees are 

 dying back. In August- September they all 

 wondered, in the Kalutara and other districts, 

 at the 



LEAVES COMING OFF THE TREES. 



Mr. Duncan: — You mean, to say that the 

 trees get bare ? 



Mr. Petch: — In some cases they get abso- 

 lutely bare. In some cases the leaves have 

 dropped from the South-West side ; and in 

 other cases there has been a general thinning 

 out. In the Kalutara district there are as 

 many leaves on the ground as in the Wintering 

 season. This is not "die back." It is easily 

 distinguishable from the other "because it 

 occurs all over the tree — both top and 

 lower branches cast their leaves at the 

 same time. People send dead branches out of 

 such trees to Peradeniya, and when we look into 

 them we find that those dead branches were not 

 killed by disease. These dead branches must 

 have been there for years : they had been killed 

 by shade. As soon as the dry weather sets in 

 these leafless branches break out into leaf. I 

 went through that leaf fall and could not find 

 any fungi. The last attack was in 1903 and 

 1909 (August.) If you study the rainfall of 

 1903 and 1909, you will find that the conditions 

 were the same in the two years. You had rainfall 

 in August, 1903, just about equal to the rainfall of 

 August, 1909. If you had any general leaf fall 

 in your trees, it would be rather interesting to 

 look at your rainfall and see whether that works 

 out correctly, that is if you were working at 

 your Rubber from 1903 to 1909. Many trees 

 shed their leaves abnormally in wet weather, 

 that is, in periods wetter than they are accus- 

 tomed to. Some of them will shed their leaves 

 when you have a hard pan, 



a substratum of rock ; 

 others when they are grown on too sodden 

 ground. There is much in the case of Hevea that 

 we do not know. 



Mr G H Masefield : — Will that rocky pan 

 account for a portion of the trees shedding their 

 leaves on a plantation ? 



Mr Petch : —That is a matter which upsets 

 the idea that shedding is due to rainfall. Your 

 trees may defoliate in groups. 



Mr Baines : — It has a good deal to do with 

 want of rain. 



Mr Petch : — It has a good deal to do with 

 rain because the worst places are both windy 

 and rainy. The worst places I have seen were 

 in the South- West wind with 180 inches of rain 

 this year. I mention all this because a good 

 many people have got frightened about leaf 

 fall, and a paragraph in a paper told us about 

 a new disease of rubber appearing in vari- 

 ous districts. That is chiefly what happened. 

 It was entirely due to wet weather, and as far 

 as we can find out no fungus whatever was 

 associated with the falling leaves. The next 

 thing which has been brought out by the wet 

 weather this year but not in this district — we 

 had some of it last year too but it was not 

 noticed— is the 



OLD CANKER DISEASE OF 1903—04 



which was supposed to have vanished. In fact, 

 last year, I wrote that I could not find a case of 

 canker when I wanted to see it. But this year 

 there is a lot of it but not in the same form as 

 in 1903. In 1903 it was found usually on the un- 

 tapped bark ; and if you read the Peradeniya 

 circular of 1904, you will find that the disease 

 was distinguished by the bark becoming a sort 

 of dirty claret colour underneath, where it 

 went right into the wood. This year it started 

 on the renewed bark (specimen shown). The 

 first thing observed is a series of small vertical 

 lines on the renewed surface. In most cases 

 the bark seems to sink round these lines so 

 that you get a sunken patch vertically. If you 

 cut that out, you will find the bark dead and the 

 cambium blackened. If you go on cutting 

 where you do not see the black lines, you wi 11 find 

 spots on the cambium. As a rule it works up- 

 wards, but does not go very far downwards. It 

 js rather peculiar that you can go on 



TAPPING THE WHOLE TIME WITH THE DISEASE ON. 



If you go on tapping as you do, once in two 

 days, you can go on with the tapping work faster 

 than the canker works. It does not kill the trees. 



WHEN THE DRY WEATHER COMES, IT STOPS ; 



and there is no more infection in such weather. 

 This specimen (shown) had one renewed surface 

 in dry weather and another in wet weather. 

 This renewal is perfect ; but the renewal in the 

 wet period is all canker. It does not spread far, 

 at any rate in this specimen it has not. So all you 

 have to show for the canker period is this one 

 strip of dead bark which is renewing already 

 underneath from the healthy bark. As far as 

 the tree is concerned, it is healthy in effect and 

 the crop is not affected, but the difficulty comes 

 here — the bark over these cankered parts will 

 be rough. Instead of the renewal coming up 

 regularly under the bark it is coming round 

 holes where the canker is there. This (specimen 

 shown) has not got far -enough in renewal, but 

 in some of the Kalutara places where they are 

 tapping on a 3 months' system — 3 months 

 here and 3 on the other side — you can trace it 

 back to eighteen months wet and dry weather 



