THE .MONTHLY BULLETIN. 



387 



Some idea of the size of the drops can be gained with a compound microscope 

 equipped with an oil Immersion lens and an eye-piece micrometer. The emul- 

 sion should be under a cover glass on a slide. It is better to separate the 

 cover glass from the slide by the thickness of a ring of quick-drying black 

 asphaltum painted on the slide. It is much simpler to take a microphotograpn 

 of the emulsion and study the print. The Dark Field Illuminator improves the 

 definition of the picture. A plate is always a little hazy owing to a slight 

 vibration of the drops. This, however, does not interfere with the accurate 

 calibration of the size of the drops. 



The so-called "miscible oils" are a commercial preparation in which the 

 emulsifier is held in the oil either by suspension or by colloidal solution. 

 These miscible oils, when mixed with water make excellent emulsions. It is 

 difficult to make a uniform product and the price at which the oil is sold makes 

 it uneconomical for orchard use. 



These principles for the selection of an oil spray were evolved during the 

 course of certain experiments performed in behalf of the Bean Spray Pump 

 Company under an industrial fellowship financed by them in the entomological 

 department of Stanford University. The details of these experiments are the 

 property of the company. 



SOME FACTS ABOUT THE ERADICATION OF 

 CITRUS CANKER. 



By A. S. Hoyt, Southern Field Deputy. 



State Commissioner of Horticulture G. H. Hecke, in order to obtain at first hand 

 a working knowledge of citrus canker and the methods employed in its eradication 

 sent the writer recently to Florida to make a thorough field investigation. Thanks to 

 the courtesy of the Florida State Plant Commissioner Wilmon Newell, the records 

 containing the history of this remarkable campaign from its beginning up to the 

 present time were freely offered for the purpose of making a study in detail. Many 

 interesting facts were noted among which the seasonal variation in the activity of 

 the development of citrus canker deserves mention. It is at once noted that the 

 month of August stands as a high-water mark for the detection of infected trees 



To oik' who is only slightly familiar with Florida conditions this fact is readily 

 explained as is also the accompanying fact concerning the development of the disease. 

 The warm seasonal rains coming during the latter part of July and August with the 

 consequent period of active vigorous growth bring about an ideal condition for the 

 development of any organisms which may have been present, perhaps for a consider- 

 able length of time but which because of climatic or other reasons remained dormant. 

 In August of 1914, 1,313 infected grove trees were found. In August, 1915, this 

 number was slightly exceeded and at the same time the largest number of infected 

 grove trees found in a single month was recorded with the discovery of 1,345 infected 

 trees. Compare with these figures the 219 infected grove trees reported in 

 August, 191(5, or the 30 infected grove trees found in August, 1917, and we see a very 

 encouraging and positive assurance I hat by the maintenance of the present standards 

 of the work, and by the continued cooperation of the United States Department of 

 Agriculture and the State Plant Board of Florida this disease, virulent and destructive 

 though it be, may be completely wiped out. , 



The eradication of citrus canker is based fundamentally on four factors ; first, rigid 

 inspection, second, prompt destruction of infected trees, third, disinfection of persons 

 and thinvs exposed to infection, and fourth, adequate quarantine to prevent the move- 

 ment of articles, especially nursery stock, likely to carry infection from an infected 

 .list lid into or through a territory which has not previously shown infection. The 

 ion consists of a careful tree to tree inspection; weekly in infected groves and 

 in troves known to have been exposed to infection, bimonthly in moves in which no 

 infection has been found and whirl, are not known to have been exposed to infection 

 hut which by their proximity to infected groves are regarded with suspicion, and 

 quarterly in' groves which have not shown infection, are not known to have been 

 exposed to infection and which are distant more than one mile from the nearest 

 infection The destruction of infected trees is aoc plished as promptly as possible 



