CITRUS DISEASES. S9 



of rain or dew on the j^oiing tissues is necessary to permit of the 

 germination of the spores and the entrance of the organism into the 

 tissues. The ordinary heavy dews of the Island arg quite often suf- 

 ficient to permit of this, but a period of wet, cloudy weather produces 

 an especially favorable situation for a severe attack. 



Except as a carrier of the infection, wind has an indirect influence 

 only, in so far as it serves to dry up the moisture in the trees and 

 so prevent infection. In this connection it has often been noted 

 that low-lying blocks of trees, or those protected by hills or heavy 

 Mdndbreaks, are, other conditions being equal, most susceptible. In 

 most groves scab has first appeared in just such situations. The 

 elimination of windbreaks to check scab is not recommended, except 

 possibly in isolated cases where they have been put in too close or 

 have become too large. 



In any block of trees the amount of scab may vary from year 

 to year, and to a less extent from tree to tree. Observations make 

 it quite clear, that this is due in large part to weather conditions 

 at. the time of blooming and for a short time thereafter. Wet, cloudy 

 weather will ordinarily mean a heavy visitation of scab, while clear, 

 sunny weather means that the frvdt comes through comparatively 

 clean. There are, of course, many exceptions to this rule. In those 

 groves which the disease has not yet reached all fruit remains clear 

 in spite of the weather prevailing. In those blocks of trees which 

 have been subject to disease, some infection will occiu' no matter 

 how bright and clear the weather may be. It has been often noted 

 that there are in most groves a number of trees, often only one or 

 two, that are peculiarly susceptible, and doubtless serve as infection 

 centers from which the disease may spread rapidly when conditions 

 become favorable. 



Very often the presence or absence of the disease in the trees of 

 a grove depends upon the time at which the bloom and flush appear, 

 it being quite common for great variations to occur in eacli block 

 of trees iii this latter regard. For example, those trees that bloom 

 during the first two weeks of Fe))rui'.r"y might escape the bulk of 

 infection owing to dry Aveather, while trees in the same l)lock and sim- 

 ilar in all respects, except as to later blooming, might some weeks 

 later be very severely attacked. 



No evidence has been secured to indicate that the stock on which 

 the grapefruit is budded, (rough lemon, sour orange, and of late 

 years, grapefruit,) has any effect on the relative amount of the 

 disease present. 



