THE MONTHLY BULLETIN. 



CALIFORNIA STATE COMMISSION OF HORTICULTURE 

 Vol. VI. July, 1917. No. 7 



CITRUS CANKER. 



By Wilmon Newell, Plant Commissioner, Gainesville, Fla. 



Pew plant diseases have attracted, during the first few years following their intro- 

 duction into tin 1 United States, as much attention as has citrus canker. Certainly no 

 disease has been the subject of such energetic investigation by plant pathologists or 

 the cause for such intensive and drastic means for its control. In fact, "control," 

 in this instance, became almost immediately a question of eradication and the present 

 warfare on citrus canker in the United States is unique in that it is the first instance 

 in the history of applied plant pathology where a systematic attempt has been made 

 to completely remove from a country the very last vestiges of a plant disease. 



Sufficient progress has been made in the eradication campaign, in Florida at least, 

 to justify the conclusion that eradication is but a question of continuing adequate 

 measures upon a sufficiently extensive scale for from two to four years longer. The 

 final elimination of every center of infection from the United States, or even from an 

 individual state, will establish an entirely new practice in the control of injurious 

 insects and plant diseases — one infinitely more practical and economical in the end 

 than a continued warfare for all time to come by means of insecticides and fungicides. 



The first case of citrus canker found in Florida was discovered on September 30, 

 1912, by the State Nursery Inspector, on Citrus trifoliata seedlings which had been 

 imported from Japan. It was not recognized as a new disease at that time and was 

 diagnosed by several plant pathologists as being an "unusual manifestation" of citrus 

 scab. Specimens taken at this time were found, months later, to be identical with 

 the disease which later on came to be known as "citrus canker." 



The disease doubtless occurred in Texas, and perhaps Alabama, as early as 1912. 

 In fact, information gathered by the writer indicates that one nursery in Texas was 

 infected with the disease as early as 1911, but such information could not be verified 

 as specimens of the "trouble" were not preserved. 



In July, 1913, the disease appeared in a nursery in a southern Florida county and 

 because of its rapid rate of spread and injury to the stock was regarded with grave 

 suspicion by the Nursery Inspector and all measures at his command were taken to 

 prevent its spread. Adequate laws for dealing with an unknown and unnamed 

 disease were not then in effect in Florida and this experience with citrus canker 

 showed the justification of quarantine laws sufficiently broad in their scope to permit 

 the quarantining of any suspicious insect or disease. 



In the spring of 1914 the disease appeared in citrus trees which had been secured 

 from the southern Florida nursery just mentioned, and the grove owners became 

 much alarmed. In May, 1914, the Florida Growers' and Shippers' League con- 

 tributed funds for a preliminary investigation and one grove inspector was employed 

 in the county referred to. By June the growers of this county realized that a disease 

 possessing a virulence previously unheard of was making havoc in their groves. 

 Attempts to control the trouble by means of sprays and by cutting out infected 

 leaves, twigs and branches, and treating the remaining portions of the trees with 

 disinfectants proved ineffective. In July, 1914, the growers in this county abandoned 

 nil hope of curing the disease and adopted a campaign of eradication consisting of 

 the destruction of the infected trees by fire, a burning oil spray being used for the 

 purpose. 



At the same time, in a county several hundred miles away, the same disease, though 

 its identity was unknown, was destroying the grapefruit plantings. Here a little 

 band of determined growers, without the knowledge of plant pathologists or state 

 officials, was attempting every control measure that ingenuity could devise and, 



finding all asurea without effect, they also came to the conclusion that their only 



hope lay in burning the infected trees. They accordingly employed one of their 

 number to seek out the infected trees and as rapidly as these were located they were 

 burned by piling "light wood" about them and supplying the torch. 

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