48 INSECTICIDES AND SPRAYING 



Other advantages of the dust method are as follows: The cloud 

 of dust envelops immense numbers of trees, one barrel of dust, it 

 is claimed, under proper conditions, being sufficient to cover five 

 hundred trees; one cannot get on too much of the dust; it com- 

 mends itself for small plants such as cabbages, currants, and straw- 

 berries; it is somewhat less expensive, both in labor and material, 

 than using the liquid spray ; one hundred large trees can be dusted 

 in one hour at an average cost of about one cent per tree (Figs. 

 67 and 68). 



Its disadvantages lie in several facts: When a strong wind is 

 blowing it cannot well be used, because one is obliged to keep to 

 windward side of trees constantly; it is best used when the dew is 



FIG. 68. A larger dust sprayer on wagon. 



on the trees or plants, thus relegating the work to the early morn- 

 ing hours; it is not especially effective against the codling moth; 

 on account of the clouds of dust it settles on horses and workmen 

 much more readily than liquid spray; is not nearly as effective 

 against sucking insects as the recommended liquid sprays. 



In connection with the subject of dust spray it is interesting to 

 note that one barrel of quicklime will make two and one-half 

 barrels of dust (air-slaked lime) ; five pounds of Paris green to every 

 barrel of lime is the proper proportion to be used against biting 

 insects; it should be repeated several times. For canker worms, 

 however, one should use ten pounds of Paris green to every barrel 

 of lime; and for potato beetles and green cabbage worms twenty- 

 five pounds to every barrel. 



