36 STATE POMOIvOGICAI. SOCIETY. 



NON-PARASITIC DISEASES OF FRUIT TREES. 

 By Prof. W. J. MoRSE, Orono. 



Some time ago your secretary wrote me requesting that I 

 come to this meeting prepared to speak on the diseases of trees. 

 Since it seemed to me impossible to do justice to so general 

 a topic in the time allotted, I suggested that the discussion be 

 limited to the non-parasitic diseases of fruit trees. When I 

 came to go over the matter in detail I felt the need of still greater 

 limitation. Just at present our orchardists are much interested 

 in winter killing of fruit trees, therefore, I think you will pardon 

 me if I limit what I have to say largely to those diseases which 

 are brought about by adverse weather conditions, and particu- 

 larly to those due to extremes of heat and cold in winter. 



Any condition which interferes with the normal activities of 

 a plant and renders it partially or wholly incapable of responding 

 to its environment is a disease. We should bear in mind that 

 there is a sharp distinction between the cause of the disease and 

 the disease itself. The fungus in plum pockets is not the dis- 

 ease, but its presence in the tissues of the host stimulates them 

 to abnormal activities and the large bladdery "pockets" are 

 produced in place of the normal fruit. Similarly the hired man 

 is not a disease (though we sometimes look upon him as an 

 affliction) but by carelessly driving his team in the orchard he 

 may be responsible for a diseased condition resulting from bark- 

 ing and wounding the trees. 



While some may object to my definition of a disease, if we 

 accept it we see that diseases resulting from non-parasitic 

 agencies are common. These are largely due to the action of 

 the non-living environment, such as conditions of soil, moisture, 

 atmosphere, heat, light, lightning, etc. I will briefly mention a 

 few of these diseased conditions resulting from extremes of tem- 

 perature. 



Sun scald is a trouble which is apt to take place in mid-sum- 

 mer on the south of young, thin barked trees, and is due to over 

 heating and drying out from bright sunlight. Also in late winter 

 and early spring, when the rays of the sun on the south and 

 southwest sides of the trees cause an alternate freezing and 

 thawing, the tissues beneath the bark are killed in patches, the 



