382 agriculture of maine. 



Character and Causes of Apple Diseases. 



If we accept a rather broad definition that disease in plants 

 includes the effect of every unfavorable factor entering into the 

 life of the plant it follows that various agencies of the living 

 and non-living environment may be responsible for the con- 

 dition known as disease. While it is not always easy or con- 

 venient to discuss the disease apart from the cause, it should 

 be kept clearly in mind that the parasite or other exciting factor 

 is not the disease. The latter is the condition induced in the 

 host as the result of the presence of the former, rendering the 

 plant partly or wholly incapable of responding to its environ- 

 ment. Therefore all methods of disease control should be based 

 upon an as extended and as detailed knowledge as possible of 

 the responsible factor or factors regardless of their nature, but 

 it is important as well to be able to recognize the outward mani- 

 festations or signs of the disease upon the host to aid in its 

 identification. The outward manifestations of plant diseases 

 are frequently not apparent until too late to remove the cause 

 and save the plant or fruit. Hence from their character and 

 mode of attack preventive measures must be largely relied 

 upon to prevent losses from plant diseases, particularly those 

 whfch attack the apple. 



Those diseases which are induced by unfavorable soil and 

 climatic conditions or other non-living agencies are said to be 

 non-parasitic. Those which result from the attacks of various 

 forms of organic life upon the host or from their presence 

 within its tissues are classified as parasitic diseases. 



This bulletin is concerned with certain non-parasitic diseases 

 and those parasitic diseases of ^ple trees and fruit in JNIaine 

 which are produced by fungi and bacteria. 



In this State fungi are responsible for the major part of the 

 loss from the diseases under consideration. Fungi are low 

 forms of plant life made up of threads of microscopic size. 

 These threads constitute the mycelium of the fungus, which 

 penetrates into the tissues of the host, causing the death of the 

 cells which compose these tissues and living upon their con- 

 tents. The conspicuous portions of the fungus which are seen 

 on the surface of the host are in most cases the fruiting organs. 

 Instead of seeds these fruiting organs produce various forms 



