Plant Sanitation in Fruit Plantations. F. T . Brooks. 255 



to say in passing that much money is sometimes wasted by 

 spraying at the wrong time. 



Finally, there are the surgical and hygienic means of dealing 

 with plant diseases. At a time when hygienic measures are 

 assuming increasing importance in the medical profession, it is 

 of interest to point out that these twin phases of ])lant sanitation 

 ha\'e long been the mainstay of the plant pathologist, and prob- 

 ably will long continue to be. Fruit trees in particular lend them- 

 selves to surgical treatment when attacked by certain diseases. 

 It is not the case here that if one member of the plant body 

 suffers, all the other members suffer with it, for the unruly limb 

 of a fruit tree can be severed with nothing but benefit accruing 

 to the remainder of the tree. Fire is the strongest weapon in 

 the armoury of the plant pathologist, and notwithstanding that 

 its frequent use in this connection is sometimes slightingly 

 referred to as a primitive and unscientific weapon, and not at 

 all in keeping with the elaboration of the twentieth century, it 

 is undoubtedly the surest destroyer of disease that exists. In 

 plant sanitation, one aims at the eradication of the sources of 

 infection. This is a point of view which should be kept constantly 

 in mind by the cultivator. It may be urged that it is impossible 

 to eradicate completely the sources of infection in the case of 

 the commonest plant diseases. Be that as it may, and certain 

 human diseases such as yellow fever have been wiped out in 

 parts of the tropics solely by the application of sanitary measures, 

 conviction is firm that many of the most serious fungoid pests 

 can be greatly reduced by destroying their breeding grounds 

 which are still often left either within or near fruit plantations. 

 It is a well known fact in medical science that in diseases of 

 parasitic origin like malaria and tuberculosis the magnitude of 

 the dose, so to speak, of the parasite frequently determines 

 whether disease is established or not. If only a few germs are 

 absorbed, the parasite may not be able to establish itself, while 

 if many are taken in, disease will develop rapidly. The same 

 factor operates with certain plant diseases, and many growers 

 here must be familiar with plum orchards which, through neglect 

 in the eradication of branches bearing Stereum purpureum — the 

 cause of silver-leaf disease, succumbed in the later stages with 

 amazing rapidity. In such cases, probably the most potent 

 factor is the great abundance of spores shed by the fungus in 

 the immediate \'icinity. 



The first principle of sanitation in fruit gardens is to avoid 

 as completely as possible any harbourage for the breeding of 

 insect and fungoid pests. This postulates the cutting off of 

 branches which are dying back and their speedy destruction on 

 the spot by fire', or removal from the plantation. If the severed 



M. S. 2 



