296 DISEASES OF CROP-PLANTS 



conditions of Barbados and on heavy soils in Antigua. In 

 Antigua Sealy Seedling is highly valued for its resistance on 

 heavy clay soils and D 95 is fairly satisfactory under the same 

 circumstances. The most strongly resistant of all canes grown 

 in the West Indies is the Uba, which is used for planting in poor 

 soils and on thin patches in Trinidad and Antigua. Even this 

 becomes severely infested and can even be killed outright by 

 root disease in combination with froghopper attack. 



Control. 



It is clear from the foregoing that it is to the general efficiency 

 of his agricultural practice rather than to direct action against 

 the fungus that the planter must Igok for the control of root 

 disease. The greatest of all safeguards against it lies in the rota- 

 tion of crops. Where this is not practicable the more thoroughly 

 the ground is worked in the necessary interval between reaping 

 and planting the better, since exposure leads to the rapid decay of 

 infective material, and tends to the sterilization of the soil. 

 Under such circumstances deep ploughing is advisable at an early 

 time. The practice of leaving the stools in " resting " or thrown- 

 out lands is a very bad one from this point of view. With regard 

 to the ratooning of infested fields, although as has been mentioned 

 above it may be possible in a good year to ^ei satisfactory re- 

 sults, such conditions are not so frequent in most of the cane- 

 growing islands as to make the chances worth taking. The 

 advantages of selecting healthy material for planting have been 

 pointed out above. The soaking of the sets in Bordeaux mixture, 

 originally recommended as a precaution against pineapple 

 disease, is of very little value against the mycelium of 

 Marasmius. 



Where the disease appears in single stools or patches some 

 local cause such as soil grubs, sucking insects, bad drainage or 

 shallow soil should be first looked for. The effects of exposure 

 may cause the disease to appear on the outside rows of wind- 

 swept fields. 



The digging of isolation trenches sometimes recommended is 

 not regarded as having any practical value. Another recom- 

 mended measure, the application of lime, must be considered 

 with due regard to the general condition of the soil and the 

 indications found of the causes of the infestation. Quicklime 

 has a directly sterilizing effect, slaked lime hastens the decay of 

 material that would support the fungus in the soil. Exposure 

 of the soil by repeated turnings is probably quite effective enough 

 for practical purposes. 



It should be noted that chemical manures applied to diseased 

 stools are wasted unless the formation of new roots has first 

 been stimulated by moisture and cultivation. 



