138 DISEASES OF CROP-PLANTS 



a closely sheltered circle around the base of the tree induce 

 conditions which invite surface infection, and should most 

 certainly be cut away. Grass and weeds should be kept short 

 all the time, not merely in the crop season. 



It is highly desirable in infested clearings, and especially 

 in the neighbourhood of infested spots, to go further and clear 

 away the soil and weeds about the base of the stems, completely 

 baring the collars, and liberally exposing the main roots so far 

 as this may be done without forming a saucer in which water 

 will stand. The treatment of the collar and the recesses between 

 the roots with lime-sulphur solution to keep the bark free from 

 moss gives an added protection of considerable value. 



All these measures are summarized in the word ventilation, 

 and cannot be too strongly emphasized. The fungus cannot 

 tolerate dry conditions and it is for the planter to take every 

 advantage he can of this weakness. 



(b) In Cacao Plantations. 



There are probably few managers of cacao plantations who 

 would nowadays plant breadfruit or avocado trees through 

 their fields. Where these trees are already established, the 

 planter who has learnt respect for root disease has two courses 

 open to him. The one is to take the utmost care of such trees, 

 to prune out dead branches, to avoid injuries to the roots, and 

 generally to try to preserve them in health as long as possible ; 

 the other is to take them out as occasion offers, removing the 

 stumps, and following out and removing every root that can be 

 got at. Striking cases have been seen where the cutting down 

 of avocado, breadfruit, or pois-doux has led to the appearance of 

 the disease in places from which it was thought to be far removed. 

 These trees are the chief victims, but there is none that can be 

 considered to be really safe. It should be the settled policy 

 of cacao planters in wet districts to leave no woody material 

 to rot in the soil if it can possibly be avoided. Where there is 

 deep shade and high humidity, any vegetable matter used as 

 mulch may be a source of danger, though one that may have to 

 be risked in view of manurial requirements. The more careful 

 and prompt the attention that is given to any appearance of the 

 disease on the plantation the less will the risks of this nature be. 



With regard to windbreaks : where experience has shown 

 that there is danger of disease arising, it is advisable to keep 

 them as free as possible from undergrowth, and to scrape away 

 any accumulations of leaves or other material from hollows or 

 other sheltered places. This can be burned or used in the pens. 



II. — Treatment. 

 The prospect of saving trees with deep-seated or well-estab- 

 lished infections is too remote to pay for the labour and skill 

 required. But experience has shown that in fields in which the 



