CITRUS CANKERS 



By Frederick A. Wolf,^ 

 Plant Pathologist, Alabama Agricultural Experiment Station 



INTRODUCTION 



The ravages of certain insect pests and plant maladies have, in a con- 

 siderable number of instances, been so severe as to cause intense alarm. 

 It has been feared in the case of several crops that their culture was no 

 longer possible in certain sections because effective means of preventing 

 the losses resulting from such ravages were not then known. Within the 

 last two years it has been realized that a new disease known as Citrus 

 canker has been introduced into the Citrus-growing sections of the Gulf 

 Coast States. This disease, beyond all doubt, is the most destructive 

 malady affecting species of Citrus, and when it was realized that its con- 

 trol and eradication were so difficult, alarm concerning the future pro- 

 duction of Citrus fruits became almost an hysteria. Those who have 

 never seen Citrus canker under field conditions regard the reports of the 

 highly infectious nature of this disease, of its destructiveness, and of the 

 difficulties experienced in its eradication as the results of an overwrought 

 imagination. The severity of Citrus canker has not been exaggerated, 

 however, and growers should lose no time in preventing its further dis- 

 semination and in effecting its eradication. 



HOSTS OF THE ORGANISM 



Citrus canker has been found to affect many of the varieties and species 

 of Citrus, and in all probability none of the species of this genus are 

 entirely immune. It is perhaps productive of more serious injury to the 

 varieties of grapefruit, or pomelo {Citrus decumana), than to any other 

 of the Citrus fruits. Seedling grapefruits appear to be more susceptible 

 to canker than the budded varieties. Some regard the injury to the 

 hardy or trifoliate orange {Citrus trijoliata) , which is extensively used as 

 the stock upon which to bud other species of Citrus, as equally severe. 

 Certain of the varieties of round oranges {Citrus aurantium) are known 

 to be very susceptible to Citrus canker and under favorable conditions 

 suffer as severe injury as grapefruits. The disease occurs also on varie- 

 ties of the sweet orange. Oranges of the mandarin group {Citrus nobilis) , 



• Published with the permission of the Director of the Alabama Experiment Station. 



3 The -writer is greatly indebted to his colleague, Dr. J. S. Caldwell, for suggestions and material aid 

 diuing the progress of this investigation and for assistance in the preparation of the manuscript. Much 

 of the chemical portion of the investigation would have been impossible but for the skillful and arduous 

 assistance of Messrs. A. C. Foster and C. W. Culpepper, formerly laboratory aids in the Department of 

 Botany of the Alabama Poh-tcchnic Institute. To each of these gentlemen grateful appreciation for the 

 several services is hereby acknowledged. 



Journal of Agricultural Research, Vol. VI . No. : 



Dept. of Agriculture. Washington. D. C. Apr. lo. 1916 



cz Ala. -3 



(69) 



