92 Problems of Economic Biology in East Africa 



quite liable to cause considerable damage unless checked by spraying 

 when the berries are still green. 



Rot of the roots is not very common, and wherever it occurs usually 

 indicates that the ground has not been properly prepared at the start, 

 and that stumps and roots of native trees have been left in the soil. These 

 are always sources of infection by root destroying fungi, the mycehum 

 of which spreads from the decaying stumps through the soil on to the 

 roots of the coffee trees. 



Dieback of the branches is troublesome in certain parts of the country, 

 particularly where the rainfall is more than 45 inches and the soil is 

 heavy. Up to the present this trouble is not fully understood, but among 

 various contributory causes rendering the trees liable to this disease are 

 unhealthy conditions of cultivation, water-logged soil, attacks of Hemi- 

 leia, overbearing, insufficient pruning, and the presence of Colletotrichum 

 cojfeanum Noack. 



Dieback is far more prevalent in Uganda where the general conditions 

 are not so favourable to coffee as they are in the highlands of East Africa. 

 A very singular dieback of the main stem has occurred more than once 

 in nearly every coffee district and has so far baffled any attempts to 

 elucidate its true cause. Nearly every case of the disease was reported 

 shortly after a heavy thunder-storm had passed over the plantations, and 

 was at first ascribed to lightning. Circular patches of trees from 20 to 50 

 in number were discovered with shrivelled and blackened foliage; and 

 there was always one tree in the centre which was more affected than the 

 rest. The least affected were on the outside, and intermediate stages 

 occurred between. The shoots bearing the blackened leaves were dead 

 towards the tips and for some distance down each shoot, including the 

 main stem, the cortex was discoloured and the cambium disorganised. 

 Unless the affected parts were cut off well below the discoloration in the 

 cortex the trees invariably died slowly back to the roots. 



On old specimens which had thus died, the cambium had been replaced 

 by a brown mycelium and very often the fructifications of a Diplodia 

 were found on the bark, and always the pycnidia of a PJioma and a 

 Phomopsis. At one time it was considered that this particular form of 

 dieback was due in the first place to the PJioma or to the Phomopsis, 

 but the few inoculation experiments which could be carried out did not 

 lend support to this view. 



The problem is an interesting one of some economic importance and 

 calls for a more thorough investigation than has hitherto been possible 

 into the relations existing between the abnormal meteorological con- 



