The Avocado: Its Insect Enemies. 27 
in combination, and similar contact insecticides in the liquid form, 
in the control of these two pests of the avocado. 
In conducting the dusting operations the equipment used was a 
large power duster (fig. 21), which is provided with a gasoline 
engine driving a fan capable of rotating approximately 2,500 revo- 
lutions per minute and of producing a forced current of air which 
is directed through the bottom of a hopper holding the dusting 
material. It picks up the dust particles, forcing the material out 
through a long pipe and producing a dense, smokelike cloud. The 
Fic. 21.—Power duster in operation against red spider on avocado trees. 
spraying work was performed the same day, a power outfit being 
employed, using one of the spray guns (fig. 20, 6) at a pressure 
ranging from 225 to 250 pounds. At the time when the materials 
were applied the foliage was dry and the temperature averaged 
ko- EY. 
In the dusting experiments several kinds of material were used, 
among them an impalpable sulphur dust. This sulphur dust is nearly 
pure sulphur, very finely pulverized, capable of going through a 
200-mesh screen. The other material used was a combination con- 
sisting of the above sulphur dust impregnated with a quantity of 
40 per cent’ nicotine-sulphate solution. In the spraying work sev- 
