PRESS BULLETIN No. 102.
Florida Agricultural Experimeun Siailon.
WHITEFLY CONTROL BY FUMIGATION, SPRAYING, AND
BY E. W. BERGER.
FUMIGATION WITH HYDROCYANIC ACID GAS.
If a grove is well isolated, that is, not less than a mile away from all
other whitefly-infested trees, especially if some woodland intervenes, and if
also the owner has the courage to quarantine against the coming of all
vehicles, then the fumigation of citrus trees in the winter months may be
.profitable. One thorough fumigation of the trees in an isolated grove should
rid them of all injurious insects to such an extent as to make it unnecessary
to repeat the operation for at least two years, and possibly for three years;
provided, of course, that all other food plants, such as Chinaberry trees,
privet, and Cape jasmine, have been destroyed. The cost will range from
a few cents per tree to more than a dollar, according to the size of the
tree. The cost of one fumigation has been estimated by experts on the
subject as equal to that of three sprayings; while in efficiency it is con-
sidered equivalent to perhaps six sprayings. This estimate does not include
the cost of the fumigating tents.
SPRAYING WITH CONTACT INSECTICIDES.
Spraying the whitefly with insecticides is not recommended except when
the trees are small-not over five to seven years old. The grove should
be isolated, as previously stated, otherwise the whitefly will keep coming in
as fast as it is killed off. It will be found to be practically impossible to
kill all the whitefly in a tree by one thorough spraying; so that in order
to keep the whitefly under control by this method, it- is necessary to spray
several times during a year. The writer has in mind one grower who sprays
twenty acres ten times a year, at a cost of about twenty cents for each
tree; and he is succeeding fairly well in keeping scales and whitefly in
check. His trees are four and five years old.
The spray used may be whale-oil soap, kerosene emulsion, or any other
good contact insecticide.
,, The whitefly can be kept out of non-infested groves in localities suffi-
ciently isolated, for a considerable length of time. The fact that thousands
of dollars may be saved in this way to a grower or a community, should
October 31, 1908.
be an incentive for all, whether directly interested or not, to co-operate in
keeping the whitefly out, or in checking its spread.
Several methods of procedure are available. By closing all private roads
and gates, especially against vehicles coming from infested districts, much
could be, and in fact has been, accomplished. The property should be
"posted," which would have the effect of keeping out many individuals who
may be carriers of whitefly, since the latter has frequently been found con-
cealed on the clothing of persons after they had left infested localities. No
nursery stock should be admitted except after it has been completely de-
foliated (leaf and leaf-stalk), and cut back to the extent of removing the
tender green-colored growth. To complete the protection, the stock should
furthermore be fumigated with hydrocyanic acid gas. When it is known
for a certainty that the section from which the stock is ordered is free
from whitefly, the previous precautions need not be taken; but the stock
should be completely enclosed to protect it from becoming infested while in
transit through infested districts. Pickers' implements from infested dis-
tricts have been excluded by growers in certain non-infested sections. This
was a perfectly proper course to follow, since it is easy to conceive of the
newly hatched larvae or the adults being carried by such means. Such
implements could, however, be made safe by a thorough spraying with some
contact insecticide. When implements are sprayed, every effort should be
made to saturate all crevices. The picking bags and outer clothing of pick-
ers should also be treated, either with carbon bisulphide or with hydrocyanic
acid gas, in some air-tight receptacle or room. (For further particulars
see Bulletin 88, page 74.)
State papers please copy.