CONDITIONS FAVORABLE <>i: NECESSARY. 9 
CONDITIONS FAVORING OR NECESSARY TO GOOD RESULTS. 
isolation OF (;ko\ i:. 
[solation in an infested grove is the most favorable condition for the 
successful control of the white fl\ by fumigation. A distance of one- 
half mile between a given grove and the nearest infested grove ia 
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 i> a common experience in newly infested groves that the 
section which first becomes infested may be very noticeably blackened 
by sooty mold for two or three years before the white 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 year--. 
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 
alt ainment of the concerted action necessary for the control of various 
(it in- pest s in that State. It is predicted that the white 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. a The 
officials Inning the matter in charge, how r ever, 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 OB 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 lawsee Bui. 61, Bur. Km.. I". s. Dept. Agrici L906), pp. L3-21. 
