286 



THE AGRICULTURAL NEWS. 



September 7, 1918. 



PLANT DISEASES. 



DISEASES OF COCO-NUTS IN JAMAICA. 



Two leaflets recently received from Mr. S F. A.shby, 



■ Govermiient Mic^obiologi^t, Jamaica, embody the information 



obtained so far in the investigation of coconut diseases in 



that island. 



The differentiation ot bud rot into two distinct disease.s, 

 one of which is believed to be of fungu.s origin, is particularly 

 intere.-ting and imiwrtant. The view which for a number of 

 years seemed justified by the available evidence vras that bud 

 rot in the Western Tropics was solely bacterial in its nature, 

 while the similar disease of coco nut and other palms in the 

 East was due to a fungus of the genus Pythium- This has 

 recently had to be modified owing to reports of bacterial 

 disease" in Malaya and elsewhere, and it seems that as a result 

 of Ashby's discoverie in Jamaica, the converse modification is 

 necessary as regards the Western forms. 



Ashby's des-ription of the twi . types met with in Jamaica 

 is as follows. In the first type, which is presumably still to be 

 regarded as bacterial, 'one or more fruiting bunches begin to 

 drop the young nuts, followed by a breaking down of the 

 limbs. In this type weeks or months may elapse before the 

 ' disease reaches and kills the heart, so that as a rule ample 

 warning is given of the progress of the disease 



'In the second type of bud rot the first symptom 

 noticed is a drooping of the heart leaf which soon dies and 

 dries up. This form of the disease give.s no warning, as the 

 tree is dead before anything wrong is noticed This kind 

 of bud rot is now very widespread in St. Thomas and 

 Portland. It has been present in these pa-ishes for years, 

 , but the hurricane of September 1917, followed by much rain 



■ towards the end of that year has caused a great increase of 

 the disease since February 19 1^. 



'The disease is due to a fungus which causes pale or dark 

 brown spots to appear on the ba.-es of the limbs round the 

 heart. The fungus gradually eats its way through the strainer 

 or thicker parts of these limbs until it reaches the heart of 

 the tender cabbage, which is rotted quickly and changed 

 usually into a soft, stinking ma.-s. It is only when the rot 

 has reached intg the heart ot the cabbage that the heart leaf 

 ' droops, dies, and dries up. The spots on the leaves and strainer 



■ of the limbs round the heart arc- not as a rule large enough to 

 ' cause these leaves to appear diseased, so that the death of the 



heart leaf is the first .-ymptom to be seen, acd then it is too 

 late to try to save the tree. 



'As soon as a tree shows a dead heart leaf it must be cut 

 down, the buds split open, chopped up, and thoroughly burnt 

 6o as to be charred to the centre It is not en<.ugh to chop ofl' 

 the limbs and make a fire on and around the unsplit buds, 

 as such fire usually does not reach into the heart. The bud 

 must be split open and chopped into a number of pieces so 

 that all the rotted parts get destroyed by the fire The fungus 

 freuuently causes sodden spots in the fibrous parts at the top 

 of the stem below the cabbage. In such cases the top of the 

 stem showing these spots must be cut off and burnt with the 

 bud. Cutlasses and axts used in splitting and chopping up 

 the diseased buds should be Hamcd in a fire on the spot 

 until the iron is loo hot to be toucl ed by the hand. 



'It is very necessary that the prompt destruction of trees 

 killed by bud rot be continued, -^a the disease may remain 

 dormant in the tops on the chler limbs for many months (as 

 long as two years in India) before penetrating into the heart. 



'Bud rot attacks trees f'f everj- ag..-, from the |ouugeat 

 to the olde.Ht. It is usually especially sevwe on deep, rich, 



alluvial soils in wet districts; in thest localities the trees 

 make a very rapid sappy growth, bear early and heavily, and 

 seem more susceptible to the disease than slower growing, 

 later bearing trees on poorer lands and hill lands, and also in 

 drier districts. Treea in well-drained land appear to be less 

 susceptible to the disease. The fungus of bud rot may 

 cause rows of spots to appear on living heart leaves, giving 

 rise to one kind of Leaf-Bite disease (Phytophthora or 

 Pythium Leaf Bite). Such trees very probably die finally 

 from bud rot.' 



The leaf-bite diseases here referred to are de>ilt with in a 

 second leaflet. 'At least four forms can be distinguished in 

 the fields of which the cau.ses were ditferent. During the 

 last couple of years two kinds have become very conspicuous 

 in northeastern parishes, three of the forms are caused 

 primarily by vegetable parasites, and in each of them the 

 heart leaves are the first part to be attacked, before being 

 pushed out into thelight. As attack occurs while the leaflets are 

 pre.ssed together on the stalk, they are killed down to the 

 same level, giving a choppexl off or bitten ofl' appearance to 

 the leaf when finally pushed out, hence ihe popular name. 



'The most frequent form of the disease is caused by the 

 pineapple fungus (Thiela'riopsis paradoxa, von Hohnel), 

 another widely spread but less frequent form, probably by 

 a small yeast. The other kind due to a vegetable para ite is 

 caused by a downy mildew (/'^■/'(7//;///d/;-ii sp.), and is more 

 local and rare. The further kind due to the rhinoceros 

 beetle {Strate^^ns ?p.) shows the leaves torn or pierced For 

 convenience the forms may be named: — 



1 Pine-apple Leaf-Bitten Disease 



2 Hard or Little Leaf- Bitten Disease 



3 Phytophthora Leaf-Bitte« Disease 



4 Rhinoceros Beetle Leaf-Bitten Disease.' 



The symptoms of the first (pine-apple fungus) type are 

 given as follows: 'The younger green unfolded and unfolding 

 leaves appear bitten oft' at the ends or show successive leaflets 

 lower on the stalks broken or reduced to stumps. Those 

 nearest the hetrt show spots on S'lccessive green leaflets 

 which bend over or break and hang down at these points. 



'Leaves just pushing up can be detected with black tips; 

 if the end of the heart leaf is cut out with the white leaflets 

 overlapping and pressed on the stalk, characteristic discolour- 

 ed patches and s[iots will be seen. Infection usually starts as 

 a yellow discolouration with a brown edge along a narrow liiie 

 beside the ribs of the leaflets; the infection runs across all 

 the leaflets overlapping at that point. Ttiese long narrow 

 spots widen to wedge-shaped patches with dark brown, broad 

 edges and a pale-btown centre, with the skin raised into a 

 blister, .so that it can be torn ofl' to expose the fibres with 

 the ti.ssue between them more or less decayed away. 



'If infection is high up, only the tips of the leaflets 

 become black. A heart leaf , may show one or more wedge- 

 like patches of di.sease. Spots are al.so present on the ;. aflets, 

 at first minute, round or oval, yellowish with depressed 

 centre, later with pale yellow centre and brown edge; by 

 union these becom« patches; in bad cases the leaf-stalk 

 (rachis) beneath the diseased leaflets is attacked by a dark- 

 brown rot, so that when pushed out the end of the limb may 

 break oft". Spots and patches show Vilack specks consisting 

 of spore masses of the fungus. The frequency of infection 

 beside the ribs of tjie leaflets is due to a line of thin cells 

 there, which regulate the opening and closing of the mature 

 Ifartets in dry aiid moist air si as to control evaporatio.o, of 

 water from the leaf pores, which are confined to the und^j 

 'sides of the leaflets, 



