482 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 13 
Comparison of Day and Night Fumigation 
The effect of the gas on the scale and the effect on the plant both 
demand careful attention in a comparison of daylight and night 
fumigation and one ordinarily acts as a balance on the other in recom¬ 
mending or condemning the practice. From the standpoint of scale- 
kill, night practice can be differentiated from sunshine practice by the 
comparative results at different parts of the tree, and in the accompany¬ 
ing table is presented such a comparison for experimental work per¬ 
formed against the black scale. 
Table VI—Comparison op Night and Sunshine Fumigation Against Immature Black Scale, 
Using a pull Dosage-Schedule in March, 1920. Each Set op Figures Represents the 
Average of Five Trees. 
Per cent killed 
Time 
Temperature 
Exposure 
Shade (N.) 
Sun (S.) 
2-4 ft. 
2-5 ft. 
Night. 
46° 
50 min. 
93 
94 
Sunshine... 
69 
50 min. 
95 
99 
Sunshine. 
71 
30 min. 
82 
98 
A study of this table shows that sunshine work at a temperature of 
69° was decidedly superior to the night fumigation at 46 degrees. This 
superiority was due unquestionably to temperature differences. Ex¬ 
periments performed by the writers show that in night work better 
scale-kill occurs at higher temperatures than at low temperatures. 
The results in night fumigation are quite uniform throughout the bot¬ 
tom of the tree whereas daylight work gives the best kill on the sun¬ 
ward side where the temperature influence is greatest, as previously 
stated. Additional experiments carried out against mature black 
scale showed an even greater difference in mortality between night 
and day work, the superiority always being most outstanding on the 
sunward side. 
Trees with a 30-minute exposure were fumigated in the sunshine 
simultaneously with those given a 50-minute exposure. These results, 
which are presented in Table VI, are of interest in showing that on 
the sunward side the kill is but slightly inferior to that for a 50-minute 
exposure whereas on the shaded side of the tree it is decidedly inferior, 
at this point giving an 82 per cent scale-kill against a 95 per cent kill 
for a 50-minute exposure. Comparing a 30-minute sunshine exposure 
at 71 degrees with a 50-minute night exposure at 46 degrees, the 
results of the daylight work are seen to be superior on the south side 
of the tree but decidedly inferior on the north side. In view of the 
