200 DISEASES OF CROP-PLANTS 



Dominica and St. Lucia, and the importance attached to it 

 could not be more strongly emphasized than by stating the fact 

 that some planters have manured their wind-belts. If the 

 advantages are so definite in these wet islands the need is all the 

 clearer where the rainfall is much lower and less well distributed. 

 In this type of situation it is necessary that the wind-belts should 

 be well-grown and dense to the base, and, to secure the latter 

 condition, it is advisable to grow some suitable plant as secondary 

 cover for the gaps which develop between the stems of the main 

 line of trees. It must be remembered that the direct influence 

 of a wind-belt does not extend very far, but the protection to 

 the first rows of lime trees is passed on by them to the succeeding 

 rows. Conversely, where dieback begins opposite to some gap 

 which lets in the wind, the reduction of the nearest trees gives 

 access to those behind, as a result of which the disease may spread 

 through a field as if it were actively infectious. 



The steady use of organic manures may be somewhat con- 

 fidently expected to increase duration ; there is little recorded 

 experience known to the writer to justify a more definite state- 

 ment. Spasmodic heavy applications of manure have been often 

 tried and seem invariably to make matters worse. 



It would be interesting to learn the effect of a system of 

 close draining established with a view to keeping moisture in the 

 soil low during the rainy season, and thus discouraging the 

 "formation of roots at levels at which they are liable to be readily 

 injured by dry weather. Some amount of natural adaptation 

 in this respect is perceptible in the differences of root level in dry 

 and wet districts. It is in this connection that the use of surface 

 mulches in places liable to drought needs careful consideration. 

 They help in such circumstances to retain soil moisture, but some 

 experienced planters hold that this good effect is more than 

 counterbalanced by their tendency to encourage root formation 

 near the surface. The local experiments on which the advocacy 

 of mulching in respect of tree crops is based were carried out 

 under relatively wet conditions and need confirmation for dry 

 ones. If the mulch can be constantly maintained there should be 

 a decided advantage, but this involves large supplies of material. 

 In this, as in all matters relating to the management of limes in 

 dry districts, the maintenance of uniform conditions should be 

 the basis of policy from the time the field is established. Tinkering 

 with the conditions after the trees have begun to fail has always 

 given disappointing results. 



The prompt removal of affected branches delays very con- 

 siderably the course of the dieback, but owing to the slowness of 

 the healing process and the tendency of disconnected wood to 

 dry out and become infested special care is needed to trim the 

 wounds flush with the stem. 



