484 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 13 
ranging from 45 minutes to one hour, yet the attempt to transplant 
these dosages and exposures to daylight fumigation under the pot- 
system has invariably been disastrous. 
It has been explained that the more successful use of liquid hydro¬ 
cyanic acid than pot-generated gas in daylight work is possible be¬ 
cause of differences in diffusion which, in the former case, places a 
weak gas at the top of the tree, the part of greatest heat. This diffu¬ 
sion, together with possible differences in physical properties of the 
gas, has appeared to render the transfer of night practice to daylight 
practice possible with a reasonable degree of safety during the winter 
months when the trees are in a dormant condition. Especially is this 
true for lemons to which no particular injury has occurred during the 
past winter’s fumigation. 
Throughout the summer and autumn trees are very active and the 
sunlight intense, both of which render fumigation at this time a very 
precarious practice. However, fumigation can be done even under 
the most severe combination of conditions provided the dosage is 
reduced or the exposure shortened sufficiently to offset their influence. 
Of course, if the reduction of dosage or exposure necessary to offset 
the injury factor reduces the scale-kill below commercial requirements 
the operation is a failure. 
Injury from daylight fumigation is characterized by leaf drop, 
particularly on the sunward side of the tree and in severe cases by 
bleaching of green fruit. The fruit pit so prevalent in night fumiga¬ 
tion is infrequent in daylight work. Ripe fruit does not appear to be 
affected at all and trees have been observed defoliated without the 
colored fruit being injured in the least. Bleached fruit, if not too 
severe, may later recolor and appear unblemished, but severe burns 
reduce the grade. It is scarcely possible to conduct sunshine fumiga¬ 
tion without considerable leaf drop. Therefore, one of the most 
important considerations in attempting this practice is to determine 
the amount of foliage that can be dropped without injury to the tree. 
On this growers are at variance. 
The writers have taken many records of fumigation during the 
active autumn period at temperatures upwards to 80° F. with exposures 
averaging 30-40 minutes. Dosages as high as 78 and 89 per cent 
schedules were used. Such practice was in general very effective 
against the red and black scales, but the injury to the trees was fre¬ 
quently very severe, and in some cases gave almost complete defolia¬ 
tion. The injury in the early morning and late evening was less 
intense than during the hottest part of the day. By sharp reduction 
of the dosage and exposure to offset the increased intensity of the sun¬ 
shine numerous orchards were fumigated at this active period without 
