228 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 3 



SOME OBSCURE DISEASES OF PEACH 



By J. B. S. Norton-. College Park, Md. 

 Introduction 



Perhaps most of our cultivated, plants are troubled with many 

 physiological diseases of more or less consequence, many of which, 

 though they may cut off the crop seriously each year, do not receive 

 notice, as their symptoms are not marked enough to attract attention 

 as specific diseases; though some are well known because so serious 

 that they could not escape notice by either cultivators or pathologists. 



It is comparatively easy to work with a disease when the cause can 

 be easily seen with the naked eye, as with most of our insect troubles. 

 And if by careful microscopic work a pathogenic fungus or bacterium 

 can be discovered, it is again a more or less simple matter. So much 

 so, that practically all of our training has been along the line of in- 

 sect and fungous parasites ; a basis for pathological work which is not 

 strictly logical, as these are only parts of the more fundamental science 

 of pathology which deals with all abnormal variations in nutrition, 

 respiration, stimulation, etc. But, we instinctively look for a parasite 

 and are baffled when we come to a serious disease without any causa- 

 tive organ other than the diseased plant itself. 



So far as I know the peach has more serious diseases, the cause of 

 which has not been definitely determined, than any other crop we 

 grow. It is only by extensive study of these under a great variety of 

 conditions that we can obtain accurate information on such distur- 

 bances in plant health, and for that reason, I wish to here give a brief 

 account of such as have come to my notice from personal experience 

 and a recent examination of the available literature. 



Not all the diseases, the causes of which are unknown may be non- 

 parasitic ; some may be caused by yet unknown bacteria, fungi, insects 

 or other animal parasites, and in that case or even if due to a con- 

 tagious ferment, as may be the case in the yellows, may come under 

 the domain of the horticultural inspector. 



Yellows 



I shall mention first what has been determined about peach yellows. 

 (See Erwin Smith, also Clinton and other recent authors.) Briefly, 

 this is a definite disease, characterized by premature ripening of the 

 fruit, which is peculiarly red blotched, internally red streaked, and 

 of poor quality, premature growth of leaf -buds, and even flower- 



