POMONA COLLEGE JOURNAL 



of ECONOMIC BOTANY 





Volume I 



MAY 1911 



Number 2 



Die-Back or Exanthema of Citrus Trees 



(A Physiological Disease) 



BY E. O. ESSIG 



HORTICULTURAL COMMISSIONER OF VENTURA COUNTY, CALIFORNIA 



INTRODUCTION 



Citrus Die-back was first described in Florida in the year 1875 by F. H. Fow- 

 ler*, but when it actually appeared in the orchards has never been ascertained. 

 In California the disease was known in San Diego county in the year 1890 on trees 

 which had been imported from Florida. From its first appearance to the present 

 time there has been much confusion in the minds of citrus orchardists regarding 

 the appearance, work and control of this disease. Since the publication of Bulletin 

 No. 8 by W. T. Swingle and H. J. Webber of the Division of Vegetable Physiology 

 and Pathology, U. S. Department of Agriculture, in 1896, a better understanding 

 of the die-back disease has become general, and since then many helpful and 

 valuable suggestions have come from B. F. Floyd, H. H. Hume and H. S. Faw- 

 cett of the Florida State Agricultural Experiment Station. In California the in- 

 vestigations have not been as extensive as in Florida, because the disease is not as 

 severe here, but several articles have been published regarding it. The first ap- 

 pears in the report of the California State Board of Horticulture in the year 1896, 

 and again in 1902. J. W. Miller, in Bull. No. 132 of the Cal. Exp. Station makes 

 a strong statement regarding its dcstructiveness in the San Gabriel valley. Ralph 

 E. Smith refers to the disease in a speech before the State Fruit Growers' conven- 

 tion at Marysville in 1907, and since that time reprints of the progress in Florida 

 have appeared in the California Cultivator from time to time. So far there has 

 never been any means of bringing together all of the known knowledge concerning 

 die-back in a connected form for the use of the citrus growers of this state, which 

 accounts in a large way for the present confusion. It is not an uncommon tiling 

 to hear growers speaking of wither-tip and die-back as being one and the same 

 thing, and ofttimes I have had this as a query from local growers. In the last 

 number of this Journal the wither-tip was fully discussed and illustrated, so as to 

 make its identity beyond a doubt. In this article I wish to make clear the physio- 

 logical disease, die-back, by presenting all available knowledge acquired in Florida 

 and in this state, together with illustrations taken in our own orchards. I shall 

 quote freely from all publications listed under the heading "Literature" further on. 



*Bull. No. 8, Div. Veg. Phys. & Path., U. S. Dept. Agricl., pp. I *, Note. 



