206 The Spraying of Plants. 



all-important question, "Which is the best?" Before going 

 into details it may be well to obtain a clear idea with regard 

 to the comparative value of liquids and powders. 



Powders are more easily handled than liquids, and with the 

 machinery now made they can be just as evenly applied ; yet it 

 is only in exceptional cases that their use is advisable. Powders 

 cannot be thrown any considerable distance, and this neces- 

 sarily limits their profitable application to the lower growing 

 plants. This becomes especially emphatic when a wind is 

 blowing, for every current of air will change the direction in 

 which the particles move, and a considerable loss of material 

 will take place. A quiet day is therefore generally the best for 

 making such applications. 



Another defect is that powders cannot always be made to 

 adhere so firmly to foliage as the liquid applications do. When 

 the foliage is dry it commonly occurs that scarcely any of the 

 powders will adhere, and this necessitates wetting the parts to 

 be treated, or else waiting until dew or rain shall have moistened 

 them so that the particles will remain where they are applied. 

 Plants having smooth foliage are particularly difficult to treat. 

 Another objection, and so far as fungous diseases are concerned, 

 the most serious one, is that we have no powders which are as 

 effective as the liquids, and for this reason alone the latter are 

 to be preferred. With insecticides, however, the case is different. 

 The best insecticides are in powder form, and when low-grow- 

 ing, rough-leaved plants are treated while the foliage is damp, 

 the poisons can be profitably and economically applied. Plants 

 grown in greenhouses can also be successfully treated in the 

 same manner, since here there are almost no air currents, and 

 the moisture may be controlled with ease. 



Liquids can be applied under nearly all circumstances. If 

 proper machinery is used, it makes comparatively little differ- 

 ence whether the plants are one or thirty feet high. In case 

 of a wind the material can still be thrown, although not so 

 well, and the operator is also under less discomfort. Liquids 

 will adhere to the parts to which they are applied, with only 

 few exceptions, and on this account greater protection is 

 afforded by them. Both fungicides and insecticides can be 

 thrown equally well by the same appliances, and since the two 

 are generally used, it would seem that liquids are to be pre- 



