CHAPTER V. 



SPRAYING AND SPRAYING APPARATUS. 



The methods of spraying of plants naturally divide them- 

 selves into two groups, (1) dust spraying and (2) liquid spray- 

 ing. 



Dust and Liquid Spraying Compared. In a general way It 

 may safely be stated that insecticides and fungicides applied 

 in the dust form to trees are not as efficient as when applied 

 in the liquid form, and the difference in efficiency is enough to 

 make it worth the extra trouble necessary to employ the liquid 

 form under all ordinary circumstances. 



The principal difficulty with the dust spray is in g-etting 

 it to stick to the foliage and fruit. It should be applied while 

 the foliage is damp. This may be soon after a rain, or while 

 the foliage is damp with dew. Advantage cannot often be 

 taken of the former condition; hence one must usually rely on 

 getting the dust spray on very early in the morning or oc- 

 casionally late in the evening. In either case it will be out of 

 the regular working hours and therefore disagreeable. The 

 wind also interferes much more with the application of dust 

 sprays than with liquid sprays. This difficulty, however, is 

 helped by the fact that in the early morning, when the dust 

 spray must usually be applied, there is seldom much wind dur- 

 ing the summer months. Another reason for the comparative 

 inefficiency of dust sprays and this applies especially to the 

 application of dry Bordeaux mixture is that the dry form can 

 never be obtained in as finely divided condition, whether pre- 

 pared at home or in the factory, as good home-made liquid 

 sprays. This means that an equal or even greater quantity of 

 the dust form cannot be as thoroughly distributed over a given 

 amount of leaf surface as can the liquid form, and hence will 

 leave more unprotected spots, through which disease or insect 

 pests may enter. The great advantage in favor of dust sprays 

 is the comparative cheapness of their application because large 

 quantities of water do not need to be hauled around in order 

 to apply the spraying material, but, as previously stated, this 



