YoL. VII. No. 163. 



THE AOKICULTURAL NEWS 



237 



THE PRINCIPAL FUNGUS DISEASES OF CACAO. 



In continuation from the last issue of the Agrl- 

 cidhiral News, the latter portion of the leaflet dealing 

 with fungus diseases of cacao, recently issued by the 

 Imperial Department of Agriculture, is reprinted 

 below : — 



PINK l)lSEA>iE. 



Occiirreive. — The pink disease was first noticed in certain 

 localities of Doniiucia, but it has snbsequently been found on 

 some estates in St. Lucia. ' 



Sytiqitoimt. — The smaller branches of cacao trees freijuently 

 become covered with a pinkish incrustation. This spreads 

 all over the surface of the bark, which eventually cracks and 

 splits and peels off. Sometimes the fungui^ penetrates deei^er 

 into the tissues of the branch. Then the branches die. 



Spread. — The fungus (Corticium lilaco-fmcam) that 

 causes this disease is only noticeable in the rainy .season, but 

 the cracked bark showing wliere the branches have been 

 attacked is easily recognized during the drier portion of the 

 year. 



Ri'medies. — This fungus may be destroyed by washing 

 the affected branches with a lime-sulphur wash. This may be 

 made by mixing 7i tt). of slaked lime with 2i lb. of flowers of 

 sulphur, with 10 gallons of water, and boiling until the 

 mixture turn.s orange in colour. This when cold should then 

 be well rubbed on to the affected parts. 



THREAD BLIIiHTS. 



Oroiirrcnce. — St. Lucia, Dominica, Trinidad, Tobago, 

 and British CJuiana. 



Si/iiiptotitx. — The fungi aj>pear as sterile threads or 

 strands of various colours, running irregularly up and down 

 on the branches and stems, and closely adpressed to the bark. 

 They generally spread upwards over all the younger twigs 

 and buds, and then, not infrequently, pass to the leaves, and 

 api)ear on their under surfaces in the form of a network of 

 fine filaments. Small branches fi'om these fungus threads 

 penetiate through the bark into the deeper tissues — thus 

 causing the death of the attacked portipns of the trees. 

 Similar branches i)enetrate into the interior, of affected leaves 

 and into the tissues of liuds, and therefore leaves and buds 

 may be killed out. 



Jiemedies. — Thorough and constant pruning, and the 

 burning of all diseased material appear to ^ have kept these 

 diseases in cheek in St. Lucia. They may still l)e found in 

 clamp, shaded portions of some estates, but can readily be 

 kept from spreading. Applications of lime-sulphur wa.sh to 

 the fungal threads is also recommended, when heavy pruning 

 cannot satisfactorily be done. 



ROOT DISEASE. 



Orriinrnrr. — Dominica, Grenada, St. Lucia. 



Si/»ijitom.<. — Trees affected wdth root disease present 

 a sickly appearance. The leaves are small and of a yellowish 

 hue. The branches begin to die from the tips, the leaves 

 wilting and frequently hanging for some time on them. 



If the roots of a disea.sed tree are laid biire it will lie seen 

 that many of the roots look black and are dead. If the bark is 

 peeled oft' from these roots, a white web of fungus threads 

 will be found bet\veen the bark and tho wood. This is 

 a typical sign of the disease. It is always to be observed in 

 the larger diseased roots, but cannot always/be noticed in the 

 younger ones. When the fungus has invaded all the roots, 

 or has circled the stem just below tlie level of the ground, 

 'the tree dies. . , 



A//r««/. — The fundus that (.Wises this disease is known 

 to attack other plants, such asMois-doux, bread-fruit, bread 

 nut, avocado pear, etc., and not mfreijuently has an attack of 

 cacao trees been traced by the spread of the fungus under- 

 ground from one of these trees jfehat" has died or is dying. 



Remedies.- — All dead pois-doEc, bread-fruit, cacao trees 

 etc., should be removed, and theiEroots extracted and burned. 

 When an area of cacao is observed; to be affected, it should be 

 isolated from the remainder of tire field by digging a trench 

 about 2 feet deej) and 18 inches wide around it — care being 

 taken to include everyone of the unhealthy trees in this 

 circumscribed area and to throw the earth from the trench 

 into the part cut off'. This encircling trench should be 

 connected with the drainage system. 



All the trees in this affected area must now be examined 

 carefully. The most badly diseased ones should be taken out 

 and btu'ned — roots and everything ; others less badly affected 

 should liave their roots laid bare and the soil removed as far 

 as possible. The diseased roots should be cut off and the 

 diseased portions removed from the soil. A good application 

 of lime should then be given in the hole that has Vjeen made 

 around the tree, ^^■hile laying bare the I'oots. 



The whole of the att'ected circle should then be thorough- 

 ly forked and a good application of quick lime at the rate of 

 about 10 ft), per tree should be broadcasted. After a time 

 ap})lications of pen manure and mulchings should be given, 

 and in the following year another application of lime at the 

 rate of about 3 to 4 ft), per tree should be made. After the 

 first general thorough forking of the affected circle, it is advis- 

 able that further forking should not be given for some years 

 unless the trees are falling back, the land being kept in good 

 tilth by heavy mulchings. Forking always causes wounds to 

 the roots, and if the fungus is present in the soil, this 

 operation is the means of spi-eading the di.sease. 



BROWN POD. 



Occurrence. — In all cacao-producing districts. 



Symptoms. — It commences as a brown, almost circular 

 .spot, usually at either end of the pods or along one of the 

 grooves on the cacao pods. The decay spreads rapidly 

 throughout the whole pod, its surface becoming brownish- 

 black in colour all over. The pod is usually soft and rotten, 

 and all the beans are destroyed. 



Spread. — This disease is caused by Dijilodia cacnoicola, 

 and spreads by means of spores that break through the sur- 

 face of badly diseased pods. 



Remedies. — This disease may (-eadily be kept in check by 

 collecting all diseased pods and, together with all husks and 

 shells, burying them with lime in trenches or pits. An 

 epidemic of this disease could be checked by spraying all the 

 pods on the trees of a plantation with Bordeaux mixture, 

 after the diseased ones have been remo\'ed. 



BLACK POD. 



Spiiptom.'i. — The attacked pods turn black and are 

 subsequently covered with the wh.it'e mycelium of the fungus, 

 from which are given off large numbers of spores. These are 

 carried by wind and rain to other pods, which they quickly 

 attack. 



Remedies. — The fungus that causes this disease is 

 Plu/tophthora onuiivora. The same remedies as recommended 

 for Ijrown pod should be applied. ' These have' proved to be 

 quite efl'ective. A reduction in sh^de might be practised in 

 some localities, for too moist and shaded an atmosphere 

 favours the growth of the fungus. 



