Apr. lo, 1916 Citrus Canker 71 



cation has for its purpose the recording of studies which are in part 

 confirmatory of previous studies (2, 5, 6, 16, 19) and which further 

 contribute to our knowledge of this disease. 



ECONOMIC IMPORTANCE 



The serious nature and unusual virulence of Citrus canker and the 

 jeopardy in which it has placed the Citrus industry can best be realized 

 when it is recalled that the Federal Horticultural Board, on January i, 

 191 5, placed a quarantine on the importation from all foreign countries 

 of Citrus nursery stock, including buds, scions, and seeds, in order to 

 prevent further introduction of the disease into the United States. It is 

 difficult to obtain figures as to the number of nursery and orchard trees 

 which have been destroyed in an effort to eradicate the disease from the 

 Gulf coast. It is equally difficult to obtain accurate figures on the amount 

 of money which has already been expended by the Federal Government, 

 together with the State horticultural boards, liberally aided by various 

 organizations and by private subscriptions, in an effort to stamp out 

 Citrus canker. Suffice it to say that the actual cost in money for eradica- 

 tion and for trees destroyed has been enormous. 



SYMPTOMS OF THE DISEASE 



Citrus canker affects the leaves, twigs, larger branches, and fruits in a 

 characteristic manner. Upon any of these parts the diseased areas are 

 light brown in color and project more or less above the surrounding 

 tissues. The cankerous areas consist of a corky mass of cells covered by 

 a lacerated grayish membrane. It can be determined with certainty 

 without a microscopic examination in case one has typical diseased 

 material, and in case one has seen the disease in the various stages of 

 development under field conditions. It is sometimes impossible to be 

 certain whether meager specimens such as are sometimes sent in for 

 identification are affected with canker or with some other leaf trouble. 

 This is especially true in the case of canker on the Satsuma orange. If, 

 however, one is permitted to make a field examination, and can thus 

 learn of the origin of the trees, and can also observe adjacent trees, typical 

 material may be found if Citrus canker is present. 



OCCURRENCE ON THE LEAVES 



The first evidence of canker on the leaves is the appearance of very 

 small oily or watery dots on the lower leaf surface. They may appear 

 on either surface, but are more commonly found on the lower leaf 

 surface. They are of a darker green color than the surrounding leaf 

 tissue and may at this stage be mistaken for oil glands (fig. 1,2). The 

 diseased areas are slightly convex, however, and within a few days will 

 have extended through the leaf, appearing on the upper surface as 



