1920.] SUGAR CANE BLIGHT IN TEINIDAD. 9 



(b.) An area of several acres in the Northern sugar district hi which 

 the soil, a fine silt, is closely compacted and probably sour. 



(c.) Scattered small patches, mostly with no immediately recogni- 

 sable defect in conditions, but strictly local, frequently 

 distinctly related to the contour of the ground, and surrounded 

 by large areas of healthy cultivation. 



7. These infestations are of a type approaching in local numbers 

 ■and severity the more widespread infestations of maximum froghopper 



years , 



8. Froghoppers are very lightly distributed through the unaffected 

 fields, therefore the damage does not arise from the locally accentuated 

 action of insects generally distributed, but from the development of the 

 insects in large numbers where the local conditions of a field or patch 

 especially favour it. 



9. In some cases the patches of infestation and damage are sharply 

 defined from the rest of the crop in the same field. 



10. From consideration of the effects of difference of rainfall in 

 -certain periods and certain districts and from local observations of 



■ soil and seepage effects, it appears most probable that the conditions 

 governing the development of froghopper infestation arise in some way 

 not understood from a soil and moisture relation. 



11. A merely backward or stunted condition of the crop is not in 

 itself sufficient to induce a froghopper infestation. There are very 

 many such fields this year which are quite free from blight. 



II. ROOT DISEASE. 



12. The fimgi capable of causing root disease of sugar-cane at 

 present known in Trinidad belong to the genera Marasmius and 



■ Odontia. 



13. They occur to some extent in all cane fields, but vary very 

 greatly in quantity and development in different fields and at difierent 



, seasons. 



14. Under conditions favourable to the cane they can be present in 

 notable quantity without any visible ill effects, existing on dead or 

 dying material only. 



15. Root disease is brought about when for any reason these fungi 

 are enabled to attack parts of the living plant. 



16. Any factor adversely affecting the vigour of the cane may 

 decrease its resistance sufficiently to allow of the development of 

 root disease. 



17. The common type of root disease consists of the invasion and 



■ destruction of the roots. Its effects are difficult to distinguish from 

 the direct effects of defective aeration or poverty of soil. 



18. There is a much rarer and much more severe type, due as it 

 appears to certain species of Marasmius, in which the base of the 

 stem is killed for several joints, the death of the whole cane following 

 in coaseiaence. 



