50 JOURNAL OF AGRICULTURE OF P. R. 



SPRAYING. 



An important pbase of grove practice, and one which with the 

 spread and increase of certain diseases will become increasingly so, 

 is spraying or some system of applying fungicides to the leaves, 

 fruits, and other parts of the tree in order to prevent fungus growth. 

 It is generally overlooked or not thoroughly understood that spray- 

 ing, as far as fungus diseases are concerned, must be entirely pre- 

 ventive, and can not be curative. This explains in large measure 

 the numerous failures experienced in spraying operations carried 

 out heretofore, although other points also enter into the situation. 



Bearing in mind that fungicides must be applied in time to prevent 

 infection, it is clear that the time of spraying must depend upon the 

 periods Avhen infection takes place, or in other words, upon the life 

 histories of the fungi involved. In the specific accounts to follow, 

 an attempt is made to indicate in as great detail as possible the proper 

 time of application of the fungicides recommended. 



Another reason for failure in spraying operations is the use of 

 improper materials as, for instance, oil emulsion, which is an insec- 

 ticide only, when a fungicide is required. In some instances spray- 

 ing material is used at too great a dilution. A still further source 

 of difficulty lies in the unsatisfactory nature of available labor, re- 

 sulting in improper application. To secure perfect protection the 

 entire surface of all susceptible growth must be covered with the 

 spray material. This is very difficult, but the more care exercised 

 in the actual spraying operation, the more nearly this ideal is ap- 

 proached and the higher will be the percentage of clean growth. 

 The average laborer tends to miss a considerable proportion of the 

 fruit and leaves of each tree, and to over spray the balance, which 

 results in loss of material and may lead to injury through burning. 



The machinery used is often inadequate for the task in hand be- 

 cause of lack of power or other mechanical defects. Improper spray 

 nozzles are often a cause of trouble, particularly in the higli-powered 

 machines, where the opening tends to become enlarged by wear, and 

 as a result the liquid is not sufficiently broken up into mist for best 

 results. 



Scarcely a grove on the Island is adequately equipped with spray- 

 ing machinery. A machine or machines that require two or three 

 weeks to cover a grove (provided everything runs smoothly, which 

 is seldom the case) are not sufficient, since efficient control of certain 

 diseases, scab in particular, necessitates more frequent applications. 



The make or type of machine is of little importance from our 



