SHEET TEN I S. 17 
Distillate* sprays have been employed by southern California 
horticulturists For many years, and at one time very extensively in 
the control of citrus scales. The accumulated experience with these 
sprays appears to have demonstrated that the results secured arc 
not entirely satisfactory. To-day distillate sprays are used only on 
a small acreage of citrus groves, having been supplanted by the more 
satisfactory fumigation with hydrocyanic-acid gas. Nothing illus- 
trates more distinctly the superiority of fumigation over spraying 
with distillate oils than the readoption of fumigation by (he more 
successful citrus growers, and the attitude of the officials of (he 
county horticultural commissions of this region who, almost to a 
man, now recommend fumigation for the control of scale-insects. 
A kerosene-water spray has found a Limited use 4 during the past 
year in Riverside and Ventura counties. 
FUMIGATION. 
Fumigation with hydrocyanic-acid gas originated and was first 
practiced in California by Mr: 1). \V. Coquillett, of the Bureau of En- 
tomology, in 1SS6, in combating citrus insect pests. Since that time 
it has gradually risen in favor as a means of destroying scale enemies 
of citrus plants until to-day it is in use in almost all the important 
citrus-producing countries of the world. The apparatus first used 
in fumigation was somewhat complicated and cumbersome, making 
the operation very expensive." As the use of this gas became more 
widespread a gradual improvement in equipment as well as methods 
has taken place, so that to-day the process is comparatively simple. 
SHEET TENTS. 
Sheet tents exclusively are now used in southern California. The 
manipulation of sheet tents and the general procedure in fumigation 
have been so clearly explained in Bulletin No. 76 of this Bureau 
that it will not be necessary to devote space to them here. The tents 
are octagonal in shape, the standard sizes being 17, 24, 30, 36, 41, 43, 
45, 48, 52, 55, and 64 feet, but larger ones up to 72 or 84 feet have been 
employed. The size of this style tent is property based on the dis- 
tance between the parallel sides, not on the distance between opposite 
corners. 
The materials especially recommended, and now generally used for 
fumigation tents in southern California, are 6^-ounce special drill 
and S-ounce special army duck, although 10-ounce special army duck 
is sometimes used in very large tents. The 62-ounce special drill is 
made of single threads twisted hard and closely woven. It is light, 
strong, and flexible. The special army duck is made of double 
--Aim. Rept. 1' S. Dept. A.gr. for L887, p. L23, 1888. 
77488— Bui. 70—09 2 
