88 JOUENAL OF AGRICULTURE OF P. R. 



The reproductive bodies of the disease are carried in different 

 Avays by rain and dew, by wind, and quite probably by insects, and 

 other agencies. Most of the mischief is accomplished by the first 

 two, one affording a ready means of spread through any given tree, 

 and the other, accounting for the spread from tree to tree as well. 

 The presence of the disease in each of the many infected groves can 

 generally be accounted for by its having been present on the young 

 trees, when they were brought in from the nursery for planting. 



In the presence of sufficient moisture on the young unfolding 

 leaves or newly formed fruit, the spore washed down from an infected 

 leaf or fruit above, or blown in by the wind, begins its development 

 by sending a delicate thread-like structure into the tissues of the host. 

 As this growth continues, the plant reacts to pr6duce the charac- 

 teristic corky outgrowths, which represent its efforts to throw off 

 the disease. It is successful in this to the extent that the disease 

 never penetrates to any great depth, nor continues to develope any 

 great length of time. The organism, however, remains alive in the 

 corky lesions, and is capable whenever conditions are right (a period 

 of wet weather) of producing a new crop of reproductive bodies. 

 It ap])ears to liold over to a greater extent in the leaves than in the 

 fruit. 



Contributing factors. 



Scab attacks only the very young growth, so that the critical pe- 

 riod during which infection is possible is quite short. In the case of 

 the leaves, this period includes the time from the first breaking of 

 the bud (when the leaves first show as green points) until the leaves 

 are full size. ]\Tost of the infection occurs while they are from a 

 quarter to a half an inch long and while the two halves are still folded 

 togetlier. Infections at this time cause distortion or the l)road scabby 

 patches over large portions of the surface, while later infections 

 occur as isolated points only and the leaf remains normal in shape. 

 New shoots coming out from old. infected ones are peculiarly subject 

 to attack. 



The small fi'uit are susceptible from al)out the time of the fall 

 of the petals, possibly before, until they are about an inch in diam- 

 eter. Infection is especially apt to take place where several fruits 

 touch, or where one is partly covered by a leaf. 



The most important factor influencing the prevalence of scab is 

 the nature of the weather prevailing at the time the flush and bloom 

 appear. For the initial growth of the disease, moisture in the form 



