CONDITIONS FAVORABLE OR NECESSARY. 9 



CONDITIONS FAVORING OR NECESSARY TO GOOD RESULTS. 

 ISOLATION OF GROVE. 



Isolation in an infested grove is tlie most favorable condition for the 

 successful control of the wliite fly by fumigation. A distance of one- 

 half mile between a given grove and the nearest infested grove is 

 sufficient to insure against appreciable interference with the results of 

 the treatment through the migration of adults between the groves. 

 In many if not in most cases 300 or 400 yards is sufficient isolation to 

 prevent the treatment being made unprofitable through such migra- 

 tions. It is a common experience in newly infested groves that the 

 section which first becomes infested may be very noticeably blackened 

 b}^ sooty mold for two or three years before the wliite fly multiplies to 

 an injurious extent in near-by sections of the same grove or in immedi- 

 ately adjoining groves. The experience mentioned above indicates 

 that in isolated groves the extermination, or nearly complete extermi- 

 nation, which can be obtained by carefully conducted fumigation, will 

 result in a condition of practical immunity over a period of two or 

 more years. 



CONCERTED ACTION. 



Ranking next to isolation as a factor favoring success in fumigation 

 for the white fly, is concerted action among the owners of groves in 

 naturally isolated groups, or among all the citrus growers in the various 

 counties. In California the organization and support of county hor- 

 ticultural commissions has solved the problems connected with the 

 attainment of the concerted action necessary for the control of various 

 citrus pests in that State. It is predicted that the wliite fly can never 

 become a serious pest where such systematic campaigns against citrus 

 insects have been organized. In Florida, Orange County has already 

 made a beginning toward the adoption of such measures against the 

 white fly, having organized a horticultural commission with powers 

 equivalent to those of similar commissions in California." The 

 officials having the matter in charge, however, have not felt justified 

 in attempting active field work on a large scale until careful experi- 

 ments shall have determined what course can be followed with a 

 certainty of uniform results. 



ABSENCE OR ELIMINATION OF FOOD PLANTS OTHER THAN CITRUS. 



The presence of food plants of the white fly other than citrus trees, 

 in citrus fruit growing sections, constitutes a serious menace and in 

 itself often prevents successful results from remedial work. For- 



« For the California law see Bui. Gl, Bur. Ent., U. S. Dept. Agric. (1906), pp. 13-21. 



