February, ’23] 
DELONG: RED SPIDER CONTROL 
89 
no wind during the application and a very uniform and thorough cover¬ 
ing of the foliage was secured. The trees were about 12 years old and 
approximately 2 lbs. per tree was used. 
There was very little difference in the amount of control secured on 
the different dust plots, the number ranging from 50% to 60%. The 
nicotine dust gave no better results than the sulphur dust alone, although 
applied while the foliage was wet with dew. The addition of lime and 
arsenate of lead seemed to make no difference in the percentage of killing. 
For several days following the application the sun was bright and the tem¬ 
perature was high which should have produced ideal conditions for the 
liberation of sulphur dioxide and consequent killing. Thus the dust 
acted only as a check and could not be considered an economic control. 
In order to get a comparative test, sprays were also used. The lime 
sulphur alone used at the rate of 1 to 65 and 1 to 75 gave a good control 
but was rendered more effective by the addition of resin fish oil or even 
laundry soap at the rate of one pound to 50 gallons. The soap although 
incompatable seemed to increase the toxicity at least 5 or 10%. 
The California recommendation of T. D. Urbahns is a much better 
spray and gave a very satisfactory control. This mixture is composed 
of a one percent lime sulphur solution to which has been added six 
pounds of sulphur paste for each 100 gallons. In California a paste 
spreader has been used, but a pound of resin fish oil soap added greatly 
to the efficiency when used with this mixture in place of the paste spreader. 
It might be quite possible and easy to control the red spider with 
lime sulphur alone if it could be used at a 1 to 40 strength but this is 
too strong for prune foliage. The tender foliage and caustic properties 
of lime sulphur must be seriously considered in choosing this spray 
formula. At certain times a solution as strong as one gallon of lime 
sulphur to fifty of water can be used without injury to the foliage. At 
other times a mixture of one gallon to seventy-five of water will cause 
conspicuous burning. The condition favorable for burning in this case 
seems to be the abundance of humidity in the air and the consequent 
slow drying of the spray as it hangs on the edges and tips of the leaves. 
If the spray dries quickly, no burning results. If it hangs on the leaf 
for some time in a liquid condition it will bum in almost every case. 
This was well illustrated by a row of trees sprayed in the evening just 
before sundown. The portions of the trees exposed to the sun dried 
and were not injured while the shaded portions upon which the spray 
did not dry, although applied first from the same tank, were burned 
